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All Comments on the AACD Report

• Brian Christy, Post-doc, Franklin and Marshall College

  Posted on: May 26, 2013

  After getting a Ph.D. in particle physics, I was thrilled at the prospect of returning to my first love in astronomy. Especially to work on a project so engaging to the imagination as the hunt for gravitational waves. There have been many posts already about how critical the GBT is to this collaboration. I will only add here that at F&M, a small undergraduate institution, we have 4 students working directly this summer with NANOGrav. I recently took 3 of them on a trip to the GBT for our conference. I wish there were words that could best describe the wonder this telescope produced. In the loud and very crucial demonstration of its scientific importance, please don't forget about its ability to inspire.

• Mark Morris, Professor, UCLA

  Posted on: May 2, 2013

  As a user of many of the forefront observatories of our time [including the Keck Observatory, HST, GBT, SOFIA, JVLA, Herschel, Chandra, XMM, and soon, ALMA], I am truly dismayed that the GBT -- a critically important element of this remarkably effective array of probes into our universe -- is being considered for retirement while it remains at the apex of its productivity. Modern astrophysical research demands multiple-wavelength approaches to most questions, and the GBT is a prime resource for the radio regime in many different areas of inquiry. Its scientific capabilities CANNOT be replicated elsewhere; although there is obviously some overlap with the VLA for a limited range of applications, the filled aperture is essential for many others. The GBT is the ideal vehicle for studying pulsar timing, time-domain astronomy, the astrochemistry of large molecules, solar system bodies, and the large-scale gas content of galaxies and galaxy clusters, to name only a few areas with which I am familiar. Shutting down the GBT would represent a woeful loss to the numerous productive scientists working in all these areas, and more. To single out astrochemistry, I would have to say that with ALMA coming on line and promising to do so much in the millimeter regime, it would be a heavy loss not to have continued sensitive access to emission from molecules at centimeter wavelengths. We grow new eyes, but retire our ears? I personally expect to continue being an avid user of the GBT until either I or it be retired from active duty.

• Gerrit L. Verschuur, Dr., Physics department, University of Memphis

  Posted on: May 1, 2013

• Clive Dickinson, Dr, University of Manchester

  Posted on: April 25, 2013

  I am a Reader of astrophysics at Jodrell Bank Centre for Astrophysics at the University of Manchester (U.K.). I am amazed that the closure of the GBT facility is even being considered. A lot of money has been put into this telescope, which really is state-of-the-art in more ways than one (largest fully steerable, active surface etc.). Furthermore, a number of new receivers are being developed for the GBT which will keep it at the forefront of single-dish radio astronomy. I've used the GBT several times and it really is a superb instrument and the facility (including the NRAO staff) is excellent. It is heavily over-subscribed and is an icon of radio astronomy - something the U.S. should be proud of. In my view, it has 50 years ahead of it, just like the Lovell telescope in the UK which was built in 1957. Keep it going!

• Victoria Kaspi, FRS, FRSC, Professor of Physics, Canada Research Chair, Lorne Trottier Chair, McGill University

  Posted on: April 11, 2013

  The Green Bank Telescope is a relatively new, world-class instrument in its prime, doing extremely high impact science. I'd have thought it would be lauded rather than recommended for divestment. While fully recognizing budgetary constraints it is also important to recognize existing and up-and-coming excellence; the NANOGrav program, heavily and critically reliant on the GBT, is a great example of world-class Nobel-potential science being done now, but which would suffer significantly should the GBT be closed. Moreover, I am member of the Canadian astronomical community which signed with the US radio astronomy community the North American Partnership for Radio Astronomy in 2003. I am concerned by the unilateral decision by the US side to violate the spirit -- if not the letter -- of the NAPRA agreement by divesting from a key NAPRA resource. That doesn't seem like much of a "partnership" decision, especially after Canada fulfilled its full and costly $40 million commitment in building the JVLA correlator and financing significant portions of ALMA as part of NAPRA. The Canadian community makes very heavy use of the GBT and would obviously consultation on the telescope's future before decisions final are made.

• Brett McGuire, Graduate Student, California Institute of Technology

  Posted on: April 3, 2013

  I'm a chemist by training, and my thesis work focuses largely on laboratory astrophysics. Over the past several years, however, I've greatly enjoyed getting to work in observational astronomy as well. I've used facilities spanning a wide range of the frequency spectrum: the GBT (cm), CSO and CARMA (mm), Herschel (sub-mm/far-IR), and Keck (IR). While each of these facilities is exciting, my work with the GBT has thus far been some of the most rewarding. It's because of the GBT that I have been able to add my name to the list of those who have detected a new molecule in the ISM! The detection of new molecules, and thus expansion of our knowledge of chemical inventories, is of paramount importance to understanding chemical evolution in the ISM. Understanding the chemical pathways to the evolution of life (understanding our "cosmic origins" as NASA defines one of it's key mission goals) is of fundamental interest not just to the scientific community, but to the entire global population. Amino acids, sugars, and other biologically-relevant molecules have been detected in meteorites for years, and more recently in cometary samples. The question remains, however, as to where in the stages of solar system, planet, and life formation these species are formed. As such, the search for these species, most notably the simplest amino acid glycine, in the gas-phase in star- and planet-forming regions has garnered great attention in recent years. But the detection of such a complex, and likely low-abundance, molecule is extremely technically challenging. It is therefore imperative that we have a thorough understanding of the chemical inventories and conditions at work in various astrophysical environments in order to select for observation those most likely to contain detectable amounts of glycine. Indeed, Rob Garrod has recently released a comprehensive study using gas-grain chemical networks to predict where glycine might most reasonably be detected with our most advanced telescope facility - ALMA. But such a prediction is only possible because of our knowledge of the available chemical inventories in the region. I did a quick search through the molecules detected in the last ten years using the information provided by David Woon's "Bibliography of Astromolecules" at www.astrochymist.org. Of the 52 new molecular detections in that time, almost a full third of them (29%) have come as a result of observations with the GBT. In fact, the GBT is responsible for *all* such new detections at centimeter wavelengths (see the attached document for a list of those molecules). While it is true that many of the molecules detected by the GBT have been subsequently identified in higher-frequency observations, many others have not. The list of those that have not include trans-methyl formate, a molecular detection which completely altered our understanding of the formation pathways of this ubiquitous interstellar weed (see Neill et al. 2012 for a discussion of this remarkable chemistry). My own molecule - carbodiimide - is also among those that have not been detected at higher frequencies. In fact, it very likely *cannot* have been detected in any observations to date. We were able to identify this very low-abundance molecule due to masing transitions which only occur at centimeter wavelengths! The GBT truly provides a powerful instrument for astrochemical observations. The enormous collecting area combined with state of the art receivers allows for extremely high-sensitivity, high-resolution, high-bandwidth observations to be obtained at centimeter wavelengths with very short integrations. Such observations, combined with the low-line density in the centimeter regime (as compared with millimeter and sub-millimeter wavelengths), allows for unparalleled opportunities for new molecular identifications. There simply is no other facility in existence that can serve as a substitute for the GBT in this capacity. The loss of these abilities will be a large blow to the efforts to further expand our knowledge of chemical inventories in the ISM. ALMA will very likely be at the forefront of discovery for the next twenty years, but those discoveries cannot happen without first understanding where we must look to find them. The GBT has made invaluable contributions in this area and will continue to do so for years to come.

• Kiyoshi Masui, PhD Candidate, Canadian Institute for Theoretical Astrophysics

  Posted on: April 2, 2013

  I am a graduate student at the University of Toronto playing a lead role in the data analysis for the 21 cm intensity mapping effort using the GBT. I work with a collaboration of scientists including members at Carnegie Melon University, University of Wisconsin, McGill University in Montreal, the National Astronomical Observatory of China and the Academia Sinica Institute of Astronomy and Astrophysics in Taiwan. 21 cm intensity mapping is a new technique for mapping out the structure of the cosmos, and is one of the most promising future techniques that will be used to gain insight into our Universe. There are now several future telescopes, either planned or under construction, that will be dedicated to the use of this technique. Over the past 3 years we have been pioneering the method of 21 cm intensity mapping, using the GBT. We have made tremendous progress toward developing the technique. The things we have learned have been invaluable for guiding the design of the dedicated telescopes. In addition we have performed several important measurements of the structure in the Universe and have an ambitious plan to continue this state of the art science using the GBT. This has all been possible due to GBT's versatile design and high sensitivity. 21 cm intensity mapping is a challenging technique, and systematic effects must be carefully controlled. Here GBT excels, due to its modern receivers, powerful back-ends, protected RFI environment, and most of all its unblocked aperture. It's full steerability has been invaluable, allowing complete freedom while observing. The loss of the GBT would be truly tragic for scientists around the world. Not only would it be a blow to 21 cm intensity mapping, but to the future or radio astronomy, when another new and exciting technique or observation is proposed and the GBT is unavailable to get a head start on the process of discovery.

• Andrea Possenti, Dr, INAF-Observatory of Cagliari

  Posted on: March 25, 2013

  The Green Bank Telescope is providing the worldwide science community with the possibility of performing observations and/or experiments which at the moment (and for few years since now) are not (will not be) possible elsewhere. This is the result of significant investments in term of state-of-art hardware, software and world-class expertise. Closing the instrument when it is now about to reach the peak of its capabilities and it is ensuring a (at least) decade-long golden era seems absurd, not only for science, but also on a mere economical consideration. Letting alone the negative impact that this choice would have on the role of the US community in the researches made possible with this kind of instruments. It may be enough to look back to the nineties, during the many years between the collapse of the previous Green Bank large dish and the completion of the new GBT. During that period the barycenter of the most valuable single-dish radio astronomy left the US, but (at least) there was the perspective of building GBT and thus to re-gain the leadership in future. Now, after closing GBT, there will be no perspective for a future reversal of the trend.

• Joeri van Leeuwen, Staff Astronomer/Assistant Professor, ASTRON/University of Amsterdam

  Posted on: March 22, 2013

  The Green Bank Telescope is the world's most sensitive instrument for scanning the Northern radio sky. Its huge collecting area, full steerability, protected RFI environment, and modern suite of receivers combine to form a survey and mapping machine that is unparalleled. The unimpeded view of its completely filled aperture means a single receiver can far outperform, at much lower data rates, any interferometer when high time resolution is needed on a large part of the sky -- for example, when searching for new millisecond pulsars to precisely measure gravity waves. With the GBT, the US operates the major facility in this hunt for gravity waves. To withdraw from that opportunity, in the GBT prime of life, would be a mistake.

• Tim Pennucci, Ph.D. Candidate in Astronomy, University of Virginia

  Posted on: March 21, 2013

  While I recognize the need for proper budgeting by the NSF in our current economic climate, it should be obvious (for reasons and criticisms I won't entirely repeat), that the divestment of funds from the GBT would be a large step backwards for US science in general. There are tremendous efforts to stimulate STEM fields in the United States and to maintain global leadership in scientific research and development; how do we reconcile those efforts with the de-funding of the world's premier single-dish telescope, just as it enters peak operational capabilities? The GBT is unique, second-to-none, and unlikely to be duplicated for decades; it can make observations and do science that cannot be done anywhere else. Such seemingly reckless, austere measures will drive away young, future, and possibly current scientists from the Unites States, whether or not their science is directly affected, to other countries that have more a more burgeoning, supportive scientific environment.

• Julia Deneva, Postdoc, Arecibo Observatory

  Posted on: March 21, 2013

  Proposing to withdraw NSF support from GBT and VLBA is a big step on the part of the US towards abdicating science leadership to other countries. China is building FAST, a 500m single-dish telescope with an active surface. Australia and South Africa will be building the Square Kilometer Array. Science talent will follow science investment. The GBT is unique in that it is the most sensitive fully steerable radio telescope in the world today. Unlike Arecibo or FAST, it can observe the Galactic Center, the location of the only supermassive black hole we can study at such close range. There are active GBT projects to search for pulsars in the Galactic Center. A pulsar discovery close to the black hole is expected to revolutionize our understanding of how spacetime behaves near massive objects. It would also prove Einstein either wrong or right in the regime of extremely strong gravity, an experiment that has not been done and currently can not be done in any other way.

• Ryan Lynch, Postdoctoral Fellow, McGill University

  Posted on: March 21, 2013

  As science and technology progress it is inevitable that some instruments and tools will be superceded by those with better capabilities. However, this is FAR from the situation for the GBT --- it remains a cutting edge telescope, unique in its capabilities among radio telescopes around the world. The GBT is vital to projects such as NANOGrav, which the astronomical community as a whole highly values. It produces high-impact science at a prodigous rate. As an example from my own work, the GBT has discovered over 60 new pulsars in the last few years alone as part of the most recent low-frequency large area survey, and several of these could turn out to be true scientific gems. The GBT and the NRAO site in Green Bank are invaluable resources to West Virginia and the surrounding region, not only as much-needed sources of technical knowledge and employment, but as unparalleled educational tools for students and teachers at all levels. The loss of the GBT would strike a hard blow to the US astronomical community, not only from the loss of scientific discovery but also from the lost opportunity to train the next generation of scientists and engineers on a truly world-class telescope. The budget situation for the NSF is difficult, to say the least, but so much has already been invested in the GBT, and it still has so much left to give, that closing it at this time would be true shame.

• Matthew Bailes, Professor, Pro Vice Chancellor (Research), Swinburne University of Technology

  Posted on: March 21, 2013

  The Green Bank Telescope is capable of experiments that are not possible elsewhere in the world due to its large collecting area and fine instrumentation suite. It seems incredulous to me that a country could invest so much in a telescope and then shut it down in its prime, handing scientific leadership in this area to future telescopes in China (FAST & QTT) and South Africa (the MeerKAT & SKA). Professor Matthew Bailes Centre for Astrophysics and Supercomputing Swinburne University of Technology Australia

• Duncan Lorimer, Associate Professor, West Virginia University

  Posted on: March 21, 2013

  The GBT is a premiere instrument in many fields. For my main interest, pulsar astrophysics, the GBT is a key instrument. It is providing breakthrough new discoveries in ongoing large-scale surveys at 350 MHz that are impossible at other observatories. An excellent example is the discovery of a millisecond pulsar in an X-ray binary system (http://www.sciencemag.org/content/324/5933/1411.short). At the time of writing, several of my colleagues are submitting a paper to science detailing a new system, discovered by the GBT, which has unprecedented potential for tests of strong-field gravity. Along these lines, the GBT has over the past decade provided crucial high-sensitivity coverage of the double pulsar system and further rich scientific awards will only be possible if these observations can continue. Timing of millisecond pulsars as gravitational wave detectors is another key science project which the GBT plays a major role. Finally, with the support of the NSF over the past five years, the GBT has enabled high-school students to experience front-line scientific research via the Pulsar Search Collaboratory (http://pulsarsearchcollaboratory.com). This project is one of many outreach initiatives at the Observatory. There is no doubt in my mind that divestment of this instrument at a time when it has not even reached the limit of its scientific potential would have a devastating effect on the astrophysics community in the US and worldwide.

• hardik, student, Mumbai university India

  Posted on: March 19, 2013

• Nicole Gugliucci, Post-Doctoral Research Fellow, Southern Illinois University Edwardsville & CosmoQuest

  Posted on: March 18, 2013

  I am disheartened that the GBT and VLBA are in danger of losing NSF support as a result of the most recent portfolio review. I understand that budgets are tight and that much funding is being directed towards exciting new projects, such as ALMA. However, there are certain scientific and educational niches that the VLBA and GBT fill in our nation's STEM program. In particular, much work has been done recently by high school and college students discovering pulsars with the Green Bank Telescope, and the Green Bank site itself provides rich educational and outreach opportunities for students and the general public. In a time when politicians talk about the importance of STEM education and training for the next generation, as well as a need for public support of science, these facilities are important if we are to make good on these promises and goals. I started my career in astronomy with the VLBA, and it would be truly unfortunate to see its unique scientific capabilities and teaching experiences cut down before its time. Thank you.

• Charles Romero, Graduate Student, University of Virginia, NRAO

  Posted on: March 17, 2013

  The Green Bank Telescope is an incredibly valuable resource for astronomers, For many science goals, it is the telescope of choice. For my research on involving the Sunyaev-Zel'dovich Effect (SZE), the combination of resolution and sensitivity make the GBT the telescope of choice for high resolution SZE observations. Additionally, having such a fantastic domestic facility enables much collaboration for observations/science and development of new instruments (often university-led) because of the staff and location of the facility. Without this facility, I doubt some of the exciting GBT instruments in the New Worlds, New Horizons review would come to fruition at any other facility.

• Jean-Luc Margot, Professor, University of California, Los Angeles

  Posted on: March 17, 2013

  The NSF portfolio review better captured the interests of the planetary science community than the earlier NSF senior review. The senior review committee included no-one to represent planetary science interests, and its recommendations received a strong rebuke from the AAS Division for Planetary Sciences (resolution approved unanimously). The NSF portfolio committee did include representatives of the planetary science community. Nevertheless, I was surprised that a fairly recent facility such as the GBT was targeted. The GBT has performed extremely well for the vast majority of my observations. I have been very impressed by the staff, hardware, and software. I would be unhappy to see funding for the GBT disappear. The impact on the immediate activities in my research group is as follows: 1) Radar targets within 5 seconds light-time. The GBT is a valuable facility for bistatic observations of the Moon or near-Earth objects (NEOs) that make very close approaches to Earth. However the GBT is not unique in that regard, and other radio antennas can be used. 2) Mercury spin state. The Goldstone-GBT setup (8.6 GHz) played a key role in measuring the spin state of Mercury. These measurements have shown that the core of Mercury is molten. More recently they provided values for the moment of inertia and for the radius of the core. http://adsabs.harvard.edu/abs/2012JGRE..117.0L09M 3) Venus spin state. The Goldstone-GBT setup can be used to measure length-of-day (LOD) variations at Venus. This is important because the dynamics of the Venus atmosphere are very poorly understood, and a time history of LOD variations can be used to track atmospheric angular momentum variations. I do not know of any other ground-based technique that can provide these data, and no spacecraft mission has provided similar data to date (with the exception of a handful of wind profiles). http://adsabs.harvard.edu/abs/2012DPS....4450702M 4) Europa/Ganymede spin state. The Goldstone-GBT setup was used in late 2011 and 2012 to measure the spin axis orientation of Europa and Ganymede, which have never been measured. We are using these data to search for evidence of librations, as a positive detection could inform us about the thickness of the ice shell. http://adsabs.harvard.edu/abs/2013AAS...22131404M 5) Of course the loss would impact all kinds of other potential uses of the telescope: experiments that we haven't conceived yet or that have been in the back of our minds but never implemented. These losses are hard to quantify.

• Alexander Young, Graduate Student, University of Pennsylvania

  Posted on: March 17, 2013

  In terms of sensitivity, frequency coverage, and sky coverage, the GBT is the most powerful single-dish radio telescope in the world. The GBT can cover an impressive range of science objectives that would be impossible with any other existing facility, from my thesis research on the high-resolution imaging of the SZE in galaxy clusters to pulsar discovery and timing to topics in astrochemistry. There is no other single-dish telescope in the world that comes close to matching the resolution and sensitivity of the GBT at the high frequency end. Without the GBT, the detection and study of gravitational waves using pulsar timing would be essentially impossible. As a host to community instruments led by a number of university-based groups, the GBT offers a unique opportunity for graduate students such as myself to develop extensive technical, scientific, and interpersonal skills while investigating some of the most exciting and important topics in radio astronomy today. With the world-class GBT, the U.S. will remain at the forefront of radio astronomy and continue to produce the highest caliber radio astronomers in the world.

• Bradley Dober, Ph.D. Candidate, University of Pennsylvania

  Posted on: March 17, 2013

  The GBT is an extremely unique instrument and delivers a unique opportunity for graduate students, such as myself, to grow into full-fledged research scientists. The science that can be performed by this telescope, such as cluster mapping and pulsar timing, cannot be performed by any other facility in the northern hemisphere. Shutting this telescope down prematurely would be ceding several areas of science to the FAST telescope in China. The GBT is crucial to maintaining our status in the global science community.

• Kent Irwin, NIST Fellow, National Institute of Standards and Technology

  Posted on: March 17, 2013

  Closing the GBT would deprive the community of a unique capability that will likely never be replicated. My group at NIST develops large focal-plane arrays, and the GBT is a particularly attractive facility for us especially at the higher frequencies. The science reach of an instrument with this resolution and collecting area at 3 mm is extraordinary. Its potential will only begin to be explored before the facility is shut down, representing a terrible waste of the funds required for construction and optimization.

• Mitchell Mickaliger, Graduate Research Assistant, West Virginia University

  Posted on: March 13, 2013

  The Green Bank Telescope is crucial to many astronomers around the world, especially those in the US. Many graduate students in radio astronomy, including me, rely on it for their thesis research. Without it, not only would some research not be possible (due to the fact that the GBT is one of the most sensitive radio telescopes in operation), but many US radio astronomers would move to other countries where there are large radio facilities, e.g. Australia, Germany. Given the cutting-edge research being done with the GBT, especially the search for gravitational waves, the closing of the GBT would take the US out of the race for what may be the next big scientific discovery.

• Spencer Wolfe, Graduate Research Assistant, West Virginia University

  Posted on: March 13, 2013

  The Green Bank Telescope has been pivotal in my thesis research at West Virginia University. I have been using this instrument to examine the extremely faint hydrogen gas that exists in the intergalactic space between our neighboring galaxies, and the GBT's capabilities make this type of research possible. Without it, my research would be nearly impossible to do anywhere else. This instrument's capabilities, versatility and dependability still place it at the forefront of research in the field of radio astronomy.

• Loren Anderson, Assistant Professor, West Virginia University

  Posted on: February 22, 2013

  I realize the budget pressure the NSF is under, but I believe closing the GBT is the wrong action. The GBT has only been operational for 10 years and is currently doing its best science. In closing the GBT, US radio astronomy would lose expertise as our experts seek employment abroad. Losing the GBT would seriously harm the astronomy department at West Virginia University. The GBT is at the heart of most of the work our grad students do for their dissertations. Without the GBT, we will have difficulty attracting the highest caliber students. The GBT also gives West Virginians and students at WVU a chance to see science in action. Each semester we bring groups of undergraduate students to the GBT and its positive impact on them cannot be underestimated. The GBT is invaluable for my science. Using the GBT, me and my collaborators have discovered over 600 Galactic massive star forming regions, doubling the number known. The sensitivity of the GBT has allowed us to discover the most distant known Galactic star forming region. Our work cannot be replicated with any other instrument. I strongly urge the NSF to reconsider the impact of closing the GBT.

• Lucas Hunt, Grad Student, West Virginia University

  Posted on: February 22, 2013

  The Greeen Bank Telescope has been useful to me as both a learning and research tool. It was one of the first experiences I had around a radio telescope in grad school, and visiting the site help give a deeper understanding during the radio astronomy course at WVU. It was used to take data for a recent research project probing HI at large redshift. It is still a very important and relevant tool in the field of radio astronomy.

• Roger Trusler, Education Administrator [ Retired ], Pocahontas County Schools

  Posted on: January 24, 2013

  Green Bank NRAO offers: "world class" leasersgip for developments and discoveries in the fields of astronomy and engineering; international scientific relationships; science education/research for students of all levels, elementary through post-graduate; invaluable contributions to the County, State, and the USA economically, educationally and technologically for the well-being of all. From an American financial standpoint, the only logical option is to spend USA Tax Dollars to support state-of-the-art constructionand/upgeades on Observatories that are or will be located on American soil/territories. Investing USA Tax Dollars in foreign countries is not a secure idea in today's world of instability. SUPPORT AMERICA FIRST!!!

• Martin Cordiner, Dr., NASA Goddard Space Flight Center / Astrochemistry Laboratory and the Goddard Center for Astrobiology

  Posted on: January 22, 2013

  In recent years, the GBT has been the world's leading telescope for the detection of new and biologically-relevant molecules in space, thus making it among the most powerful tools available to mankind for the study of astrobiology. The GBT has been a crucial instrument for astrochemistry and astrobiology research at NASA, and will continue to be at the cutting edge in this field with its newly-available instruments and planned upgrades. The GBT is, by a significant margin, the best telescope in the world for the study of carbon chains and anions in molecular clouds and star-forming regions, as demonstrated by recent publications (Cordiner et al. 2011, ApJ, 730, L18; Cordiner et al. 2013, ApJ, submitted). As a result of the GBT's superior instrumentation and efficiency, to perform this research using the Effelsberg telescope would have taken a prohibitively-long amount of observing time (about 5-10 times as long as with the GBT.) We are also performing new studies of molecular emission from comets with the GBT that are impossible with any other single-dish telescope. The time-variable nature of comets combined with our demanding sensitivity requirements makes this research impossible with the Effelsberg due to the length of time required to reach the same sensitivity with that telescope. These GBT studies will be of fundamental importance to cometary science in their own right, but also represent essential preparatory work for subsequent, more detailed followup using ALMA.

• Bill Howard, Retired astronomer, N/A

  Posted on: January 15, 2013

  Since October I have been developing a White Paper about the problems that are developing in the Federal funding of astronomy. They are happening in other sciences as well. The Paper can be found at the following URL and it will be updated based on the reactions I receive from our community. It really calls for a paradigm shift. See:https://dl.dropbox.com/u/59120192/PortfolioReviewThoughts.pdf

• Andrew Baker, Associate Professor, Rutgers, the State University of New Jersey

  Posted on: December 7, 2012

  I respect the time and effort invested by the members of the Portfolio Review Committee (PRC), but for three reasons, I view their report as one of many possible responses to the charge from NSF, written by one of many possible realizations of a review committee. FIRST: the PRC's assessments of which technical capabilities are "critical" and "supporting" for tackling the science questions of the Astro2010 Science Frontier Panels (SFPs) clearly diverge from those articulated in the SFPs' own reports. Three relevant examples: (i) The Cosmology and Fundamental Physics (CFP) panel identified gravitational wave astronomy as its area of discovery potential, and co-ranked a pulsar timing array and fast "electromagnetic" followup of gravitational wave events as "needed capabilities." The PRC ranked a pulsar timing array as "supporting" and specifically *optical* followup as "critical." (ii) The Galactic Neighborhood (GAN) SFP identified astrometry as one of its two discovery areas; of the three ground-based efforts highlighted as examples, two involved radio VLBI and one involved wide-field optical imaging. The PRC deemed radio VLBI to be "supporting" and wide-field optical imaging "critical." (iii) The Galaxies across Cosmic Time (GCT) SFP identified the epoch of reionization as its discovery area and assigned its "most important" rating to the development of new facilities for observing redshifted 21cm HI emission. The PRC rated this capability as "supporting," behind a "multiplex optical and infrared spectroscopy" capability judged to be "critical" even though it did not figure in the GCT report at all. Since the PRC report did not justify these reassessments, I would consider them to be a reflection of dispersion in scientific taste rather than a set of fundamental value judgments. SECOND: I suspect a review committee more familiar with the limitations of the Effelsberg 100m telescope (whose poor RFI environment I can attest to from painful experience), the Arecibo Observatory, and the phased JVLA would have been less quick to endorse these facilities as acceptable replacements for the GBT. THIRD: although it was not mentioned in Chapter 2 of the PRC report, I would personally endorse *preservation of scientific breadth* as an important guiding principle in reshaping the AST portfolio. By this metric, the sheer uniqueness of the capabilities that the GBT and VLBA can bring to bear on NWNH's key science questions makes their preservation an urgent priority. Moreover, their loss would impoverish other elements of the AST portfolio: clear scientific synergies with JVLA and ALMA programs would evaporate, the diversity of research supported by the AAG program would suffer, and one of the last remaining platforms for development of radio-wavelength instruments by university groups would disappear. Effectively, the PRC report's recommendations promise to boost the success rates of proposers to "aggressively funded" AAG and ATI programs by extinguishing a wide swath of radio-wavelength science and instrumentation research. This would be an especially damaging blow in an area that has little overlap with NASA and DOE funding priorities, and where breadth lost at NSF is therefore breadth lost forever. MY REQUEST TO NSF: Please do everything in your power to preserve the ability of U.S. scientists to pursue the most compelling GBT and VLBA science. (I would put GBT pulsar timing and supporting searches at the top of this list: the work has Nobel potential and is being led by U.S. astronomers for a fraction of the operational cost of LIGO.) If the prospect of "divestment" is merely a fig leaf for closure, then the portfolio review process (no matter how orderly) will become a stain on the national reputation. MY REQUEST TO THE COMMUNITY: Let's take a look at how we might deploy NSF AAG funding more efficiently, by finding better ways to couple grants with observing time allocations, and by establishing best practices for preparing and reviewing proposal budgets. And let's remind our members of Congress of all the good research, development, and outreach that is done with NSF-funded facilities and grants, so that we can get ourselves back on a more positive budget track.

• J. Christopher Howk, Associate Professor, Dept. of Physics, University of Notre Dame

  Posted on: December 5, 2012

  I am very concerned with the prospects of closing the GBT, and I feel the portfolio review undervalues its true worth. Even if tough decisions need to be made about how we spend the resources given, I cannot agree that the GBT should not be considered one of our most important observational resources. The work being done at the GBT spans a huge range of topics in astronomy and planetary science. Much of the work can be considered truly ground-breaking. I'll point particularly to the pulsar searches and studies that are on-going with the GBT. These studies probe fundamental physics, including exquisite tests of relativistic physics. No other telescope in the world can match the GBT's capabilities in this area. Beyond its collecting area and its best-in-the-world receivers, the interference environment at the GBT is significantly better than most existing radio facilities, including Arecibo. It is thus a unique instrument in all of the world. The GBT is a state-of-the-art instrument that is producing cutting-edge science. If one is considering conserving the most important NSF-funded facilities, I believe the GBT must be included in that list.

• D.J. Pisano, Assistant Professor of Physics, West Virginia University

  Posted on: November 28, 2012

  Dear NSF: While I applaud the efforts of the portfolio review in trying to balance the scientific return of current and future facilities with the demands of a tightening budget, I am extremely concerned about the future of US astronomy if we close down relatively new, cutting-edge facilities like the GBT to build new facilities that are years away from delivering any scientific results and that do not replace the lost capabilities. Previous comments have described many excellent science capabilities that will be lost, many of which are recommended by the New World, New Horizons decadal survey, so I will limit my comments to one that has not been widely discussed: observations of diffuse HI. The New World, New Horizons report highlighted the key question of how baryons cycle in and out of galaxies as one to be addressed in the next decade. Theory and simulations suggest that one dominant route for gas to enter galaxies is through cold, filamentary flows of gas from the intergalactic medium. Due to their low column densities (log N(HI) < 19) and large sizes (about 25 kpc widths), these filaments can only be imaged in HI with single-dish radio telescopes; interferometers act as spatial filters making the structures invisible. Furthermore, high angular resolution is needed along with low system temperature receivers to detect and resolve filaments. Finally, since these structures are found relatively close to bright galaxies, a clean beam with low sidelines is required to avoid confusion with other sources. These requirements make the GBT the only telescope capable of imaging diffuse HI structures down to log N(HI) = 17. While NSF-supported (via a recent CAREER grant) surveys are ongoing with GBT, they already are opening up new insights into the supply of gas for star formation in galaxies. Without the GBT, this work will be nearly impossible to do with Arecibo (due to its high system temperature and sidelines) or Effelsberg (due to its sidelines and RFI environment). The only new single-dish radio telescopes under construction or planned that may be capable of these observations are in China: FAST and the proposed 100-m telescope. If the US wishes to maintain its worldwide leadership in radio astronomy and continue to train people in STEM fields (regardless of the careers they pursue), it is critical that telescopes like the GBT remain open.

• Frahad Yusef-Zadeh, Professor, Northwestern University

  Posted on: November 28, 2012

  Dear NSF Director, I am writing this letter in regards to the NSF/AST Portfolio Review Committee (PRC) recommendation for NSF to divest from the NRAO Green Bank Telescope (GBT). I am sending this message echoing my strongest opposition to closing the GBT and am requesting your reconsideration of this decision. Given all the financial constraints, it is natural to prioritize available instruments and try to retire old instruments that have already provided a proven impact (e.g., CSO, Mopra). However, it is unimaginable to think that a unique facility like the GBT can be replaced by another instrument so early in its life and so orthogonal to the scientific objectives radio astronomy. The GBT is a relatively new instrument that is slowly exploring new high frequency domains between 30 and 80 GHz with great sensitivity and versatility. One would think that a powerful new instrument like the GBT should be given time to realize its full potential and impact in the astronomical community. As for limited available budget, I suggest a delay in building new instruments until the full capabilities of newly constructed telescope are realized. I have had two graduate students who did their PhDs based mainly on GBT observations of the Galactic center and supernova remnants. One is now at Berkeley and the other at Goddard Space Flight Center. I have a third graduate student who is finishing his thesis by analyzing radio recombination line survey of the Galactic center and a fourth graduate student who is working on archival data to make accurate spectral index maps based on several frequencies that have used both the VLA and GBT. There is a variety of traditional scientific topics that can be explored with the GBT, but also nonstandard topics that can potentially address the nature of $\gamma$-ray emission and the dark matter. To this end, GBT data give the most accurate spectral index measurements at radio wavelengths with powerful implications on the mechanism producing $\gamma$-rays, as viewed by $Fermi$. In addition, the spectral index distribution at high frequencies has been considered to be due to the contribution of electrons and positrons produced as the byproduct of dark matter annihilation. In this picture, the electrons and positrons created through the annihilation of a relatively light ($\sim$5-10 GeV) dark matter particle can provide a new population of electrons at energies less than the annihilation energy of WIMPS and produce synchrotron emission with distinct spectral index value. Although this picture is by no means unique, it does make predictions that only GBT observations can address. I can argue that GBT is beginning to move the forefront of millimeter (3-10 mm) astronomy by observing the sky in many different molecular lines as well as in broad band continuum. With current theoretical modeling of cosmic rays, interacting with molecular gas, GBT is in an excellent position to have a long term impact in this area. Furthermore, millimeter line emission from molecular gas should contain signatures of this interaction and GBT should have a major role in our understanding of Astrochemistry of molecular gas. I can confidently say that the closure of the GBT would have terrible consequences in the Galactic center research area. I hope you will consider supporting funding for researchers to use this under-appreciated instrument. Sincerely, Farhad Yusef-Zadeh

• William Robbins, Technical Specialist, NRAO

  Posted on: November 20, 2012

  Dear NRAO, NSF-AST, AUI, and any others concerned with the portfolio review. Hello, my name is William (Bill) Robbins. I work at the Owens Valley California VLBA Station. I have been employed by the NRAO for just over 12 ½ years. I am proud to be associated with a team of such professional and dedicated Technicians and Engineers. Part of the success of the VLBA is the staffing of each segment of the overall instrument. Located at each site, forty hours per week, are two Technicians. Each of us is on call two alternating weeks and two weekends of each month. When there is a problem, any time, day or night, clear or stormy, hot or cold, that may hinder the collection of data or the operation of a dish, we respond. Our mission is the safe and effective maintenance and support of the VLBA so as to be able to maximize the amount of time that data may be successfully gathered for Scientists both in the U.S. and abroad. This is a skeleton type crew. With two Technicians located at each site, the overall cost of manpower is minimal. Each of the ten VLBA antennas is located in a remote location. This minimizes interference that would be a problem if they were located in an urban type setting. By being in a remote area, that means that what supplies sites need are typically bought in that local area. This may range from something simple such as copy paper to something as complex as the oil and grease that is used for the antenna. To close the VLBA not only means that the Technicians would stand to lose their careers and homes, but that the local economies WILL lose too. Let us take a closer look at the geographic area of the VLBA and who represents those locations. Mauna Kea Hawaii is the most westerly dish. This is represented by the 2nd Congressional District Brewster Washington, represented by the 5th Congressional District. Owens Valley (Big Pine/Bishop) California, represented by 25th Congressional District. Kitt Peak Arizona, represented by the 7th Congressional District. Pie Town New Mexico, represented by the 2nd Congressional District. Los Alamos New Mexico, represented by the 3rd Congressional District. Fort Davis Texas, represented by the 23rd Congressional District. North Liberty Iowa, represented by 2nd Congressional District. Hancock New Hampshire, represented by 2nd Congressional District. St. Croix, U.S. Virgin Islands, the most easterly antenna. This is a spread of over 5,000 miles tip to tip of the array. This also is a list of towns or areas that will be immediately financially affected by the closure of the VLBA. Are these representatives aware of what is about to happen in their districts? We have responded to the science community concerning the “divestment” of the NRAO G.B.T. and V.L.B.A., but have we gone forward and told the American people what they stand to lose in the way of scientific capabilities for a miniscule cost? In the second week of August 2012, there was a young man and his parents that came to the Owens Valley Site for a tour. This young man was 15 years old and is interested in a career in Astronomy. He and his parents were taking, as an early Christmas present for the teen, a tour of many of the western U.S. telescopes. They were on their way to Arizona next. This young man is basing his future on astronomy. The VLBA and the GBT both have capabilities that no other telescope has in the world. If they are unfunded and closed, then, so is this young mans’ education, future, and dreams. It is not the intention of this letter to go into the fact that my future, my disabled Wife’s future, the future of all the dedicated Technicians at the sites, the Operators and Data Handlers in New Mexico, along with support staff also located in New Mexico, are all hanging in the balance here. It is the intention of this letter to notify the world and the American people that the NRAO IS at the forefront of world class astronomy instruments that serve not only our American scientists and students, but also scientists and students the world over. The NRAO has designed and maintains these instruments for less than a penny per dollar of the NSF budget per year. If these instruments are closed and dismantled, then one can NEVER be replaced for the cost of all ten currently in operation. That, along with the loss of education, knowledge, hopes and dreams of students and scientists alike would result in pure waste and loss, non-recoverable. Respectfully William “Bill” Robbins, Owens Valley Site Technician

• Daniel C Homan, Associate Professor, Department of Physics and Astronomy, Denison University

  Posted on: November 18, 2012

  I am deeply concerned about the recommendation of the review committee to close the VLBA. The phenomema of the formation, collimation, and acceleration of relativistic jets is still not well understood. Yet accretion onto the supermassive black holes that create these extraordinary jets is perhaps the most powerful sustained conversion of mass into energy in the Universe, capable of influencing the evolution of entire clusters of galaxies through the outflow feedback mechanism. These jets and the processes that create them may also play a pivotal role in the transport of angular momentum that allows matter to fall inward and ultimately accrete onto the supermassive black hole. Only the VLBA has the angular resolution, sensitivity, and regular time sampling required to directly image the jet and measure jet velocity, acceleration, and deceleration on the parsec scale. We are just now reaching the point where we can usefully measure jet acceleration in large enough samples of jets to tease-out the complicated relationship between genuine changes in Lorentz factor and line-of-sight effects. The greatly expanded bandwidth and sensitivity of the VLBA over just the last couple of years is creating new opportunities... making it possible to study the spectra and polarization of fainter and fainter parts of the jets, giving us the opportunity to measure magnetic field and particle properties of entire jet cross-sections, rather than just the brightest regions. To close the VLBA at this time, just as it is bringing these new capabilities to the Astronomical community, would be a terrible mistake. I should also add that the time-domain, structural changes that the VLBA can directly observe make it a wonderful scientific outreach instrument. As an example, I recently used a 'movie' from our MOJAVE program of the TeV blazar, 1222+216, to teach undergraduates about point-of-view effects in special relativity (see http://personal.denison.edu/~homand/superluminal/).

• Craig L. Sarazin, Vanderbilt Professor of Astronomy, University of Virginia

  Posted on: November 9, 2012

  I believe that the closure of the GBT and the VLBA would be a disaster for astronomy, both in the US and worldwide. The GBT is the most important single dish radio telescope in the world. It operates for a very wide range of frequencies. Recent technical work has made it extremely effective at mm wavelength. At lower frequencies, it is the most important instrument for studying pulsars, for example. The VLBA is the most effective VLBI facility in the world. If funding is very tight, it would be better to delay the construction of new facilities rather than close working, world-class facilities in the middle of very important scientific programs.

• Matthew Lister, Associate Professor of Physics, Purdue University

  Posted on: November 8, 2012

  To the AST Portfolio Review Committee Members: In response to your portfolio review report of NSF-AST funded astronomy facilities, I would like to draw to your attention the indispensable role that the NRAO's Very Long Baseline Array (VLBA) plays in helping us understand high-energy processes in the Universe, and in training future scientists. I am currently the P.I. of a long term NRAO key project (MOJAVE: Monitoring of Jets in AGN with VLBA Experiments: www.physics.purdue.edu/MOJAVE) that is performing the largest ever investigation of the complex structural and magnetic field evolution of a complete sample of extragalactic jets. Powered by billion solar mass black holes, AGN jets are among the most energetic phenomena known in the Universe, and dominate the sky away from the galactic plane at many wavelengths. They played a key role in shaping the structure and evolution of the earliest galaxies, and their extreme properties make them ideal laboratories for studying high energy physical processes that cannot be explored elsewhere. There are currently large gaps in our understanding of how these outflows are collimated and accelerated to extremely high velocities, and high-resolution polarimetric VLBA imaging is one of the best tools for providing observational constraints on theoretical models. At present, the VLBA is the only instrument that offers sufficient polarimetric performance over a wide range of observing frequencies for AGN jet studies such as MOJAVE. Other existing VLBI networks, such as the European VLBI Network, are ad-hoc arrays of telescopes of varying capabilities, and cannot produce extremely high-fidelity linear and circular polarization images Furthermore, since the VLBA is dedicated solely to VLBI, it is the only telescope able to provide the regularly-spaced images that are needed for studying the complex dynamics of superluminal jets. This unique ability of the VLBA to produce "movies" of phenomena that occurred several billion years ago is of great fascination to the public, and has been used effectively in outreach (e.g., http://personal.denison.edu/~homand/superluminal/). The unique capabilities of the VLBA have greatly enhanced the science of NASA's Fermi mission, with programs such as MOJAVE providing crucial structural information necessary to interpret the mechanisms of gamma-ray emission in extragalactic jets and gamma-ray bursts. (e.g., http://www.nasa.gov/mission_pages/GLAST/news/radio_telescope.html) The VLBA is an invaluable facility for training the next generation of astronomers in the United States. Since arriving at Purdue in 2003, I have had considerable interest from students who are interested in doing research related to the MOJAVE project (so many I have had to turn many away, unfortunately). I have allocated a large portion of my NSF and NASA funding for the MOJAVE project toward supporting students (over 25 total to date), including four recent Ph.D. graduates, and several undergraduates who have gone on to Ph.D. programs in physics and astronomy at major research universities. By working with data from the VLBA, my students and others across the country are gaining valuable experience with interferometric techniques, which are rapidly expanding beyond the radio regime and becoming an indispensable tool at other wavelengths as well. By virtue of being the highest angular resolution imaging instrument in astronomy, the VLBA continues to make exciting discoveries not only in AGN jet physics, but also in many other areas, including supernovae, masers, our galactic center, and stellar systems. The loss of operating funding for this instrument would be a severe setback to observational radio astronomy, and would have a serious impact on the research programs of myself, my students, and colleagues. Yours sincerely, Matthew Lister Associate Professor of Physics Purdue University

• Robert Zavala, Astronomer,

  Posted on: November 7, 2012

  A closure of the VLBA after the hard work in response to the NSF-AST Senior Review is very disheartening. NRAO made great strides by obtaining outside support and making technical improvements to the telescope. Now, after meeting the challenge of the Senior Review the Portfolio Review Committee recommends divesting from the VLBA. The VLBA is a unique instrument that cannot be replaced by heterogeneous VLBI arrays. VLBA observations are essential to understanding high energy phenomena in galactic and extra-galactic science. VLBA measured parallaxes are used to understand the evolution of young stars with no other means of obtaining their distance. The VLBA is the only instrument that provides directly measured extragalactic distances independent of the systematics present in the rungs of the cosmic distance ladder used to measure the Hubble constant. The polarization capabilities of the VLBA are far ahead of the VLBI arrays that are proposed as replacements. The presence of the VLBA is a part of the “balance of investments” which the Portfolio Review Committee was apparently charged with maintaining. To divest from the VLBA is to remove a significant resource that cannot be replaced by other instruments. These comments are my personal views in response to the NSF-AST Portfolio Review Committee report.

• Namir Kassim, Radio Astronomer, NRL

  Posted on: November 5, 2012

  The creative potential of flexible, observatory-class facility instruments derives from the collective imagination of a broad user base catalyzed through experience. Initial, pundit-driven “big science” drivers are often superseded by the unpredictable nature, and beauty, of scientific discovery. These processes take time, and scrapping the GBT and VLBA, whose collecting area, frequency range, and angular resolution will remain world-class for the foreseeable future is very unfortunate. That critique is not pursuant to the Portfolio Review panel, whose report was thoroughly logical, but to the problematic premise of their charge that detoured the ASTRO2010 roadmap in a troubling direction for US astronomy, to the bewilderment of astronomers everywhere.

• Nissim Kanekar, Associate Professor, National Centre for Radio Astrophysics, India

  Posted on: November 4, 2012

  I strongly feel that the recommended closure of the GBT and VLBA by the Portfolio Review committee will have disastrous implications for US and international radio astronomy. Both facilities have unique capabilities that are unmatched by any other telescope and that will remain unmatched for at least the next decade. As such, the notion that these are "old" telescopes is very misguided. Indeed, the GBT is by no stretch of the imagination an "old" telescope, having seen first light just a decade ago. Instead of closing down such outstanding facilities, which represent very large capital investment, it would be better to instead equip them with new instrumentation (at relatively low cost and benefiting from new technology) to tackle new scientific challenges. An example of an outstanding scientific problem that critically needs the GBT is the detection of pulsars on short-period orbits around the Galactic Centre, which would allow us to test general relativity in the extreme strong-field regime (which is inaccessible by other methods). It has been shown that the optimal frequency range for such searches is ~ 12-20 GHz. Quite simply, the GBT is the _only_ telescope in the world that can carry out both the initial discovery experiment and the follow-up precision timing studies to address this problem (of the possible substitutes mentioned by the Portfolio Review, Arecibo cannot observe the Galactic Centre, while the high-frequency performance of the Effelsberg dish is not comparable to that of the GBT). The installation of a new wide-band 15-GHz receiver on the GBT and an improved pulsar backend (both of which are in the pipeline, at fairly low cost) will enable outstanding science in this field over the next decade. A number of similar science drivers for both the GBT (e.g. detecting gravitational waves through pulsar timing) and the VLBA (e.g. astrometry) have been mentioned by other colleagues in this forum. While it is fair to say that the Portfolio Review committee were faced with very difficult choices, aiming to achieve most of the science goals of the Decadal Survey with about half the budget, the approach taken and the outcome are both very questionable. If not overturned, the recommendations have the potential to set back radio astronomy by many years.

• Adam Deller, Veni Fellow, ASTRON

  Posted on: October 30, 2012

  The VLBA's attributes - full time operation, wide frequency coverage, frequency agility, relatively wide field of view and its nature as a well-characterized instrument - make it unique many times over. Many of its capabilities are irreplaceable and will doubtless be highlighted by others, but I will comment on just one - low-frequency astrometry. Astrometry below 5 GHz is challenging due to ionospheric effects, but the steep spectra of many radio sources (such as radio pulsars) preclude astrometric observations at the normally-preferred frequencies of 6-22 GHz. The relatively wide field of view of the VLBA, coupled with the flexibility of its correlator, allow the identification and utilization of calibrator sources much closer to the target than is generally possible with other arrays, greatly improving the astrometric quality. The proof of the unrivaled nature of the VLBA for pulsar astrometry can be seen in the results to date - of the 35+ sources with a VLBI parallax measured at low frequency, more than 75% were measured with the VLBA (including *every* VLBI pulsar distance in the northern hemisphere), and the best accuracy obtained with the VLBA exceeds that of any other array by an order of magnitude. The VLBA is capable of accurately measuring distances to sources spread over the majority of the Galaxy, covering the majority of the known pulsar population. On the other hand, any other existing array is limited to a tiny, relatively nearby Galactic volume containing less than 5% of the known pulsar population. Without the VLBA, the ability to map and study the Galactic pulsar population, plus all the attendant science probing the ionized interstellar medium, will simply not exist.

• Robert A. Preston, Chief Scientist, IND Directorate, JPL/Caltech

  Posted on: October 24, 2012

  The potential loss of the GBT and VLBA would be disastrous to U.S. astronomy. Closing old facilities that are past their scientific prime is a reasonable approach to make budgetary room for new even more capable instruments. But that is not case here. Both the GBT and the VLBA are unique forefront observatories probing at the edges of our understanding of the universe. No other existing facilities or those proposed in the future match their scientific capabilities. Moreover, such action could irreparably weaken the U.S. radio astronomy community.

• Dipankar Maitra, Postdoc, University of Michigan

  Posted on: October 24, 2012

  As an astronomer who studies transient X-ray binary systems, here are a few reasons why my collaborators and I think defunding VLBA is not a good idea: - The VLBA is a completely unique instrument, providing the only full-time, dedicated access to the highest-angular resolution imaging and astrometric data. - Other VLBI networks are ad-hoc, operating in a few short sessions each year, so would not be able to replace the VLBA - and are terrible for the sorts of transients we study (if you don't have a dedicated VLBI facility, you have to get lucky with when the transients go off). - The new upgrades to the sensitivity and frequency coverage of the VLBA have made it much more powerful facility, able to make deep observations of faint compact sources. - The new software correlator has allowed it to be used as a survey-science instrument for the first time. - Closing the facility before making use of these fantastic new capabilities would seem to be a huge waste of investment funds, for want of a few million dollars per year.

• Colin J. Lonsdale, Director, MIT Haystack Observatory

  Posted on: October 23, 2012

  Defunding the GBT and VLBA would be deeply unfortunate for US astronomy, and would misjudge the technology-driven promise and cost-effectiveness of these facilities in coming years. The prioritizations of the Decadal Review, based on favorable budget projections markedly different from those constraining the Portfolio Review committee (PRC), need to be reassessed. The PRC faced a particularly difficult charge, necessarily leading to value judgments regarding the relative merits of facilities whose operations were not explicitly ranked in the main decadal survey report. Three flagship radio astronomy facilities were considered for defunding, namely Arecibo, the VLBA and the GBT. The VLBA and GBT were lowest ranked and it was recommended that they should be removed from the NSF AST portfolio, along with other items. Loss of NSF support would mean virtually certain closure of the GBT and VLBA. The operating funds thus released would contribute to decadal survey priorities including new facilities and a midscale instrumentation funding line within AST. The severe budget austerity assumed in the portfolio review analysis will cause damage to the astronomy enterprise in the US, beyond that contemplated for any scenario in the decadal survey report. If efforts to improve this budget outlook are unsuccessful, the central question is not how we prioritize the best new projects, but how we can strike a balance between innovation and damage. The PRC was charged with answering just this question, by examining the balance between permitting support for exciting new initiatives, and termination of support for highly productive and cost-effective existing facilities. Realistically, the VLBA and the GBT together represent at least $300M in current replacement cost, yet consume <5% of this per year in operating cost. New facilities incur fresh capital cost, as well as typically 10% of that capital cost per year in operations, so to be competitive with existing instruments like VLBA and GBT, any investment in significant new facilities on scales of tens of $M or greater must be extraordinarily efficient, setting a high bar. It is generally and implicitly assumed that newer is better, and that replacement cost for older facilities is a poor measure of value, but in the case of large radio telescopes, this is a bad assumption. For radio telescopes like the GBT, VLBA and Arecibo, the bulk of the construction cost goes to accurately focusing radio waves, and accurately steering the structure. The instrumentation to detect signals in the focal plane and subsequently process them is a relatively small fraction of the total cost, and is readily upgraded over time to profoundly benefit from Moore’s law, now and for many years to come. These telescopes continue to focus and steer splendidly, and in this basic function continue to be state-of-the-art. At centimeter wavelengths, reflectors are required for large collecting area, and our existing large reflector-based facilities simply cannot be replaced at affordable cost either for construction or operations. Newer is not significantly better in this arena. A key conclusion follows directly: Closure of the GBT and VLBA will result in permanent loss of state-of-the-art capabilities with low operating cost as a fraction of current value, directly impacting US leadership and global research capacity. The savings from such closures are unlikely to lead to new capabilities of comparable current dollar value to the US astronomy community. In short, this would cause a lot of damage for relatively little benefit. The PRC was asked to assess the innovation/damage balance without reopening debate on the science program laid out by the Decadal Survey. The practical reality, however, is that scientific priorities are affected by what is perceived to be both technically and financially possible. If the decadal survey committee had been asked to choose between new facilities, and closure of the GBT and VLBA, would they have chosen the latter? Or would a severely constrained budget outlook have tempered the scope of scientific ambition, leading to decreased need for new instrumental capability and hardware procurement, with correspondingly more emphasis on observations, astronomer salaries, and training? These key questions concerning Decadal Survey prioritization underline a need for further community review.

• Dayton Jones, Principal Scientist, JPL/Caltech

  Posted on: October 23, 2012

  I am writing to emphasize the scientific importance of the astrometric capabilities of the Very Long Baseline Array (VLBA), as was noted in the New Worlds, New Horizons report. While other international VLBI arrays are capable of high-precision astrometry, the VLBA is unique in its combination of stability, calibration quality, frequency coverage, declination coverage, and (with the current program to increase the observing bandwidth) sensitivity. The enhanced VLBA sensitivity is particularly important for phase-referenced astrometry because it will allow angularly closer references sources to be used, reducing systematic errors. The VLBA has been an essential component of the long-term maintenance and improvement of the planetary ephemeris, a fundamental tool for studies of solar system dynamics, tests of general relativity, pulsar timing, and interplanetary spacecraft navigation. This has been possible through long-term, high-precision measurements of planetary positions obtained by combining VLBA astrometry of a spacecraft orbiting a planet with a solution for the spacecraft orbit from Deep Space Network Doppler tracking. VLBA observations of the Cassini spacecraft currently orbiting Saturn are a prime example, and similar VLBA astrometry of the Juno spacecraft will be possible when it enters Jupiter orbit in a few years. Future missions to other solar system objects will only increase the value of VLBA astronomy for the planetary ephemeris. Note that the VLBA is able to cover well the full declination range of objects in the ecliptic plane. The fact that multiple communities, including some outside of traditional radio astronomy, rely on the planetary ephemeris raises the possibility of additional sources of support for continuing VLBA operations. Indeed, international support of the VLBA has already been obtained by NRAO. This makes the continuation of the unique VLBA capabilities highly cost effective for NSF. The VLBA contributes to development of the US radio astronomy workforce because VLBA users tend to become experts in the theory and practice of interferometry in a way that most users of the VLA/EVLA do not. Since interferometry is a powerful technique used in many fields, increased expertise in this area is valuable for the US community at large. Dayton L. Jones Principal Scientist Jet Propulsion Laboratory 4800 Oak Grove Drive Pasadena, CA 91109 dayton.jones@jpl.nasa.gov

• Joseph Lazio, Principal Research Scientist,

  Posted on: October 22, 2012

  The Portfolio Review was an admirable approach to a difficult problem. The NWNH Decadal Survey provided guidance on an ambitious program for astronomy, designed to probe the frontiers of our understanding and excite new generations in science. Unfortunately, the NWNH Decadal Survey was built on what we now realize to be a baseless foundation, namely it assumed that the NSF Astronomy budget would double over the coming decade. Given the mismatch between assumed budget from NWNH and the budget projections for the remainder of the decade, NSF Astronomy turned to the community for guidance about how to proceed. However, one of the boundary conditions for the Portfolio Review was essentially to try to execute the Science Program (Chapter 2) of NWNH. That portion of the Portfolio Review Committee's charge was too restrictive. The Portfolio Review Committee should have been allowed to go further, assessing what portions of the NWNH Science Program essentially could not be accomplished without making the assumption of a nearly doubling budget. Further, the conclusions of the Portfolio Review seem at odds with the goals stated in Chapter 2 of the AACD report and appear almost nonsensical to many of our international colleagues. For instance, the Portfolio Review Committee notes that "older and less competitive facilities" may have to be closed in order to enable new facilities. Indeed, the radio astronomy community has a history of doing exactly this. Both the 140 foot at Green Bank and the 12 m in Tucson were shut down by NRAO in order to make way for the 100 m GBT and ALMA, respectively. Yet, some of the facilities for which the Portfolio Review recommends "divestment" are not only *not* "old" or "less competitive," they are internationally unique. As a first example, the Very Long Baseline Array is simply unparalleled, at any wavelength. It provides *routine* sub-milliarcsecond resolution, and even better astrometric precision, and operates from 0.3 GHz (92 cm) to 86 GHz (0.3 cm). This span of wavelength, a factor of 270, is equivalent to a single instrument operating from the J band in the near infrared to the soft X-ray (0.15 keV). Similarly, the GBT officially became operational barely a decade ago, spans a comparable wavelength range as for the VLBA, and is a powerful instrument for *multiple* science frontier discovery areas identified by NWNH. (At minimum, the GBT is relevant for time domain astronomy and gravitational wave astronomy, and has been used for aspects of finding extrasolar planets.) Moreover, while the Portfolio Review Committee recommends divestment from a suite of world-leading facilities operating at radio wavelengths, the international community is busy making substantial investments in facilities and instruments, not only because of the recognized science potential but also because of the value for all levels of STEM education. In summary, the Portfolio Review was initiated with good intentions, but, if the Committee's recommendations are adopted, the results will be disastrous for the recognized U.S. leadership in this field.

• David J. Thompson, Multiwavelength Coordinator, Fermi Gamma-ray Space Telescope Large Area Telescope, NASA Goddard Space Flight Center

  Posted on: October 22, 2012

  In an era when so much progress in astronomy and astrophysics involves multidisciplinary work, it is sad to see serious consideration being given to “divesting” unique facilities like the GBT and VLBA, since divestiture is tantamount to shutting off access to these resources by the broader scientific community. In my field of gamma-ray astrophysics, where we work with a broad range of international partners at all wavelengths, the GBT and VLBA stand out as particular multiwavelength success stories. The GBT has been the premier northern hemisphere gamma-ray pulsar discovery and timing facility, and conversely the gamma-ray sky has proven to be a valuable source of information leading to new radio pulsar findings. As much as we like to work with our colleagues at Effelsberg, we know that there is really no comparison. Similarly, the VLBA is where we turn for studies of jet sources like blazars and microquasars, and we have benefitted tremendously from the pulsar astrometry only possible there. All other VLBI operations are intermittent and require more difficult analysis; the VLBA is unique. In its Senior Review last year, NASA faced a similar situation of constrained financial resources. The choice was to continue operating all the orbiting astrophysical instruments, because each offered the prospect of unique and continuing scientific contributions. It was also clear that the small savings from shutting down an operating satellite would not provide the resources to build a new one. Clearly, NSF is not NASA, but there are certainly parallels worth considering.

• Frank Schinzel, Staff Scientist, University of New Mexico

  Posted on: October 22, 2012

  The recent NSF AST portfolio review makes recommendations shaping a bleak future for US radio astronomy. Was it just a few years ago during my time as graduate student that the golden age of radio astronomy was declared, with many new exciting developments across the entire field, ranging from the EVLA, through ALMA, to many more opportunities exploring new parameter spaces and with the SKA looming on the horizon. In light of tight financial budgets also the astronomical community is charged to take a hard look at their expenses, but we should not forget to keep a balance between new developments and operating highly successful state of the art facilities. During my graduate studies I have made extensive use of the VLBA, be it archival or with new observations, and we are only beginning to grasp the full capabilities this technology provides. The VLBA is the only dedicated VLBI array in the world, providing the US with leadership in this technology. Divestment or even shutting down this instrument that still holds huge potentials with regard to the science and future technological developments would be a mistake. This is well demonstrated by the fact of the high interest and continuing support to build and operate similar infrastructures in Europe, Australia, and Asia, with the EVN, CVN, KVN, VERA, LBA, ... and to venture out into space for example with the Russian Radioastron mission to achieve even greater resolutions. But none of these operate either full-time or are as efficient and as accessible than the VLBA. Losing these vital facilities, the VLBA and GBT, would mean not only losing leadership in a large area of radio astronomy, but it would also reduce accessibility to telescopes for student training from institutions in the US and elsewhere that are not able to afford to buy telescope time. Even if alternate funding is found to continue operation of these facilities, access to those with the best scientific ideas in the community will most likely be lost. I urge the decision makers to carefully consider the impact a divestment in these facilities would have and how we can sustain a vital US role in the radio astronomy community in the spirit of the golden age of radio astronomy.

• Helene Courtois and Brent Tully, , Univ of Hawaii, USA and Univ of Lyon, France

  Posted on: October 22, 2012

  Mapping Large Scale Structure in the Universe: The Role of GBT Comments by Helene Courtois and Brent Tully The Scientific Problem A tremendous effort has been made over recent decades to acquire redshifts to galaxies in order to map large scale structure. These maps are distorted from real space by perturbations from the cosmic expansion. It is inferred from the dipole temperature variation that our Galaxy has a deviant motion of over 600 km/s. Attempts to explain this motion in terms of the observed distribution of matter remain unsatisfactory. The determination of peculiar velocities requires the measurement of galaxy distances but current studies are not deep enough. Our failure to understand the origin of the 600 km/s motion of our Galaxy is one of the outstanding problems in observational cosmology. The Role of GBT The need is to map distances to of order 200 Mpc (15,000 km/s). Only two methodologies extend usefully to this regime. One makes use of the properties of Type Ia supernovae but depends on serendipitous events and results in coverage with low volume density. The other exploits the correlation between galaxy luminosity and rotation rate, the Tully-Fisher Relation. The accuracy per target is not as great with this second method but it is applicable to the majority of normal spiral galaxies, hence to tens of thousands of galaxies within the domain of interest. A measurement of a distance with this technique requires two observations: a photometric measurement and a kinematic measurement. There have been breakthroughs regarding the former, first, with the availability of satellite mid-infrared coverage of the entire sky with WISE and, coming soon, comparable coverage at optical bands with Pan-STARRS and SkyMapper. For the kinematic measurement, demonstrably the most accurate practical determinant of a spiral galaxy’s rotation is given by the width of global neutral hydrogen profiles, observed at rest at 21 cm. For practical purposes, there are only two facilities in operation that can provide the necessary HI profile information. Arecibo Telescope is one of these but it operates over a restricted part of the sky and can only observe sources for a short interval as they transit. The other is GBT. This telescope can observe 85% of the sky and can track for long integrations. The only other telescope seriously being used for this sort of work is Parkes Telescope. This considerably smaller telescope is much less sensitive but is used to give access to the 15% of the sky south of the GBT limit. The Effelsberg Telescope has been used for galaxy HI observations but although it has been in operation for 40 years it has made minor contributions to the field. GBT is being used in ongoing programs by several groups to extend the sample of galaxies with accurate distances. There is the realistic prospect of reaching a sample of 10,000 galaxies within a few years. The consequence will be detailed maps of large scale galaxy flows. If distance measures at 200 Mpc do not bracket the source of our 600 km/s motion then there will be something very fundamental to explain. More probably, this information will clarify the extent in depth and specific locations of the irregularities causing our 600 km/s motion. The maps will be rich in details regarding the evacuation of voids and flows along filaments to cluster nodes. The analysis of the velocity fields results in maps of the distribution of matter today that can be translated back in time to initial conditions. In turn, this information can be used as input for constrained simulations in efforts to reproduce the observed structure. In the absence of GBT these important programs would be seriously compromised.

• Helene Courtois and Brent Tully, , Univ of Hawaii USA and Univ of Lyon, France

  Posted on: October 22, 2012

  The revival of Cosmic Flows research is only possible thanks to GBT as we describe in the accompanying letter.

• Elizabeth Jensen, Associate Research Scientist, Planetary Science Institute

  Posted on: October 19, 2012

  The following letter is being distributed at my personal EPO activities (including amateur astronomy groups): Dear [house representative], Our nation and its economic recovery is at risk. The Obama administration is proposing cuts to NASA and the National Science Foundation (NSF), bringing forth measures to shut down or sell off national resources such as the Green Bank Telescope. 85% of the USAs economic growth is attributable to technological change; the contribution from NASA is around 33-43% growth or $1.50 to $1.80 return for every $1 spent. On the stock market, this would be considered an excellent return on an investment. The NSF's return is comparable. Don't cut our future short. Our country needs you to counteract the administration's cuts and increase scientific funding before it's too late. Sincerely,

• Mason Keck, Graduate Student, Boston University

  Posted on: October 19, 2012

  I want to express my concern regarding the NSF/AST Portfolio Review Committee (PRC) recommendation for NSF to divest from the NRAO Green Bank Telescope (GBT) and Very Long Baseline Array (VLBA) by 2017. The GBT is a premier facility at 0.1-116 GHz and is an important complement to facilities such as ALMA. Furthermore, the time domain and angular resolution capabilities of the VLBA are unmatched by any facility in the world. The money saved from closing these facilities is not worth the science capability lost.

• Erik Reese, Dr., University of Pennsylvania

  Posted on: October 19, 2012

  The GBT is a world-class observatory enabling a wide range of astrophysical studies with continued potential for growth. The rapidly advancing high frequency observations are filling a niche that no other telescope in the world can do. It would be a major blow to the astronomical community to lose such a unique, versatile observatory.

• Eric J. Murphy, Postdoctoral Scholar, Carnegie Observatories

  Posted on: October 18, 2012

  Like many others astronomers, my colleagues and I were itching to take advantage of the GBT's new high frequency capabilities as they started ramp up around 2009. After a 2.5 year observing campaign, which included significant undergraduate involvement and a senior thesis, we published our survey results this year only to see that the Portfolio Review Committee is recommending that the GBT be shut down. This is a mere 3 years after the program was able to commence, and leaves the possibility for potential GBT follow-up investigations as a non-starter, which is just mind boggling. By any measure, that is an embarrassingly short lifetime for one of the flagship observatories in the United States, as the GBT with all of its new, state of the art high frequency instrumentation clearly has no equal in the world. There is no need to get into technical details that quantitatively justify this claim, as this has already been done elegantly by a number of others. However, it is worth stressing the point that with focal plane array technology starting to come online in large pixel formats, the GBT will undoubtedly continue its role as the leading single-dish radio observatory in the world for the foreseeable future. Closing the facility right when such instrumentation is ready to again transform this already powerful observatory is a shortsighted, fiscally irresponsible solution to a much larger problem, as it will take years, and significantly higher investments, to return to where we are now through recommissioning or new construction.

• Lynn Matthews, Research Scientist, MIT Haystack Observatory

  Posted on: October 18, 2012

  The United States cannot hope to maintain its role as a world leader in radio science if its first response to a crisis is to close two unique, cutting edge facilities, the GBT and VLBA. It defies logic to invest millions of taxpayer dollars into developing world class instruments, only to shut them down before they can even reach their full scientific potential. This sets a very dangerous precedent. In a time of budget crises, maximizing the return on existing instruments should be one of our highest priorities. None of the options suggested by the Portfolio Review Committee as an alternative to the GBT and VLBA offers a viable substitute for these facilities.

• Doug Gobeille, Professor of Astrophysics, University of South Florida

  Posted on: October 17, 2012

  There are few words I can add to those who have commented before me. It goes without saying that the VLBA and GBT represent not only one of the best investments in the current US porfolio, but also add invaluable data to their respective parameter spaces. These are instruments without equal or replacement across the planet and some of our primary instruments for the continued investigation of long standing astrophysical queries, but further the tip of the spear in our ability to tilt toward new horizons in astrophysics. These tools not only enable researchers at the graduate, doctoral, and post doctoral level, but also our invaluable undergraduates who will continue to explore the unknown. The grandeur, scale, and breathtaking capabilities of these instruments is a constant source of motivation, innovation, and inspiration for the future of astronomy and astrophysics. These pre-existing facilities represent the most fiscally responsible path available to us to push the boundaries of our current observational techniques. Radio represents one of the lowest cost/benefit investments in all of modern astrophysics. Put simply, our pre-existing investment, low cost upgrading, and cutting edge telescopes, the VLBA and GBT, represent a prudent and fiscally responsible path in astronomy, whereas shuttering them now will only lead to higher investments down the line in either the recommissioning or replacements.

• Doug Gobeille, Professor of Astrophysics, University of South Florida

  Posted on: October 17, 2012

• Elizabeth Jensen, Associate Research Scientist, Planetary Science Institute

  Posted on: October 17, 2012

  For some reason, the file I referred to in the earlier comment did not upload, so here is the web address for it to download: http://acs-consulting.com/wp-content/uploads/2012/04/JensenPresentation.pdf

• Elizabeth Jensen, Associate Research Scientist, Planetary Science Institute

  Posted on: October 17, 2012

  In the big picture, the cuts to government spending in general, and to science specifically is fundamentally flawed (see Keynesian economics). I would like to see all of our diverse communities coordinate to apply pressure to our House representatives to restore and increase funding for sciences. Attached below is a sample presentation that was effective with my home (Texas) representative. Areas in which to have an effect on the people who hold our country's purse strings include special interest meetings in which they speak or debate (often they will take questions), letters to the editor pointing out that science funding is in the interest of the local community, and requests for meetings with our representatives. It takes about 1 day of your time to make a measurable push. Recruiting local amateur astronomy groups can help with increasing the pressure. _Always remember to present your position as being in the best interest of your audience._

• Alan Marscher, Professor of Astronomy, Boston University

  Posted on: October 17, 2012

  The loss of the VLBA and GBT would remove too large an area of parameter space relative to the cost savings. The VLBA covers an enormous range in the combination of angular resolution and time domain. As one example of the impact this would have, I do not understand how the decadal survey's recommendation of participation in a new Cherenkov array to study very high-energy gamma-ray emission from active galaxies could lead to scientific understanding without the ability to study the objects with high angular resolution. The LSST will open up a range of sensitivity and time resolution in the optical, but without the VLBA there would not be comparable ability to study the new phenomena in the combined utlra-high resolution and time domain that the latter provides. The GBT similarly has observing capabilities that are unmatched by other instruments. The VLBA and GBT represent relatively recent investments by the NSF, are unique in their capabilities, and are still hitting their scientific stride. Preserving them for the use of the US astronomical community should be a high priority.

• Shep Doeleman, Assistant Director, MIT Haystack Observatory

  Posted on: October 17, 2012

  In these austere fiscal times it seems most prudent to invest in and leverage upgrades in existing and very capable facilities. This would argue for getting the maximum out of our capital investments in large telescope collecting areas, which are most hard to come by. The recent low-cost bandwidth upgrade at the VLBA is a great example of how using rapidly advancing signal processing and industrial trends can result in large (x2-3) sensitivity increases. Through partnership with universities and international collaborators, the NRAO VLBA team has delivered an astonishing leap in both bandwidth and processing power for this unique facility. Further, it would appear that the VLBA accomplished much of what it was asked to do by the Senior Review panel, including a successful campaign to secure non-NSF funding for operations. If the VLBA were to be de-funded, we would likely not see a facility with its capabilities for many many years. Other responses here have reminded us that the Decadal Review priorities were set using a very different set of fiscal assumptions than those adopted by the Portfolio Review. In the light of present fiscal conditions, the VLBA looks like an exceptionally good deal - one well worth preserving beyond the few-year timeline currently being considered.

• Huib van Langevelde, Director, Joint Institute for VLBI in Europe

  Posted on: October 17, 2012

  I am very worried that a world-leading scientific nation like the US pulls out of VLBI science. It is to me very obvious that VLBI has key information to contribute to many current astronomical themes. I sense that the threat to the VLBA comes from a lack of visibility when it comes to great science themes and outreach, but this is almost like blaming scientists that they do hard experiments. VLBI may not be popular, but is one of the keys in understanding high energy phenomena, details of star-formation, origin and fate of massive stars and it calibrates the distance scale of our Galaxy and Universe. Pulling out of science -and pulling out of technically challenging science in particular- dries up the source of innovation in our culture.

• , ,

  Posted on: October 16, 2012

• Thomas Krichbaum, Senior Staff Scientist, Max Planck Institut für Radioastronomie

  Posted on: October 15, 2012

  The VLBA is a unique instrument, which is absolutely important for modern research and for the education of the next generation of radio astronomers. ALMA is now build for research at the highest observing frequencies. At present huge efforts are made to establish VLBI phasing at ALMA, so that ALMA can be used soon as a single big telescope in a global VLBI array. Without the full VLBA, millimeter-VLBI with ALMA could only be done in a very limited way. We need the VLBA to perform mm-VLBI with ALMA. This will give images with a few 10 microarcsecond resolution, thus allowing to study the finest details in distant black holes. The combination of ALMA with the VLBA in the 40- 95 GHz range will enhance the image fidelity by a large factor and will facilitate numerous new discoveries, both in galactic and extragalactic astronomy.

• Kurt W. Weiler, Radio Astronomer, Computational Physics, Inc (formerly NRL, now retired)

  Posted on: October 15, 2012

  With the mega-projects such as JWST and ALMA consuming much of the funds available for astronomy, I believe that it is incumbent upon NSF to find a global solution rather than closing state-of-the-art ground-based instruments (such as VLBA and GBT) that are critical for scientific progress at other wavelengths and resolutions and for training the next generation of students and postdocs. Review committees, no matter how august, given limited charters, are not going to solve the problem. Creative solutions such as cost sharing, reduced operations, and stretching out new construction all need to be considered. The recommendations for maintaining student and postdoc training are all well and good, but where will they observe? I personally feel that the Senior Review (in part because of their very limiting charter) did not do a service to the community and I fear that the current committee is similarly constrained, yielding a similarly limited result.

• Enno Middelberg, Staff Astronomer, Ruhr-University Bochum

  Posted on: October 15, 2012

  I would like to draw attention to a few points which should not go unnoticed. First, the quality of data from VLBA observations is much better than from any other VLBI array. It is a well-debugged instrument with streamlined operations, and the data are a joy to use and calibrate. This is in stark contrast to other facilities. Second, the VLBA staff are doing fantastic work in supporting observations. Many of my projects would not have been possible without people supporting weird ideas or allowing me to try new things. Of course also for normal projects the support is great. Third, the small VLBA antennas are ideal for survey work, and wide-field VLBI surveys are just now becoming feasible because of the new backends and correlator. Fourth, the recent enhancements in sensitivity and frequency coverage draw attention from users outside the classical VLBI community, because suddenly these people realise what VLBI observations can do for them. This tendency should not be underestimated: the VLBA has essentially turned the VLBI technique from something only highly specialised astronomers would try to a more generally-used instrument which is not more difficult to use than state-of-the-art instruments at optical facilities. In light of these points it would be foolish to shut down the VLBA.

• Alyssa Goodman, Professor of Astronomy, Harvard-Smithsonian Center for Astrophysics

  Posted on: October 13, 2012

  Others' recent eloquent comments (e.g. Bolatto on why Arecibo plus Effelsberg does not equal the GBT; Sievers on instrumentation sacrifices for GBT) make the correct and important case for why the GBT is a unique instrument in the world today, and how NRAO leads the world in the development of new radio astronomy techniques and instrumentation. The US is clearly losing its lead in the optical and infrared world, with the advent of giant telescopes funded by governments other than our own. The US cannot do this in radio astronomy too, or we will stop being the source of the best, most creative, most productive astrophysicists the world has ever seen. When I think about a world without the GBT or anything like it, I think about scientists trying to interpret ALMA or JVLA data without the context of "low spatial frequency" data. As Alberto Bolatto correctly points out, this critical contextual information *cannot* be attained using Arecibo or Effelsberg. A decade ago, we had FCRAO and Haystack to do some of this work, but those facilities are now gone. The LMT is still somewhere off in the future, suffering from technical difficulties, and Mopra is hanging on for dear life. Yes, CCAT will help with some "short-spacing" issues, but it's not coming for years either. I watched what happened as the KAO was decommissioned to make way for SOFIA, which left a near-20-year gap in the training of US far-IR instrumentalists and observers. Herschel happened, and Europe rose to prominence. We cannot do this to mm and cm-wavelength astronomy without acknowledging that we run the same risk NASA and the US community did when it decided to "cut everything" to make way for SOFIA. It's not just that the US will lose out from a jingoistic point of view: the world will lose out on our contributions--which have been driving so many fields forward. The VLBA's work on mapping out the three dimensional structure of our Galaxy and our Universe cannot be underestimated in value. Maser parallaxes are the most accurate distance determination we know how to make for faraway objects, and there is literally no other instrument in the world today that can make those measurements. I am sure many others will make this point, but it is one important enough to be repeated again and again. Most importantly, the US has a tradition of letting scientists, even very young ones, take risks using its expensive facilities. The more we move toward a "one instrument to rule them all," politically fraught, committee-based, science community, the more we risk losing the great discoveries these risks yield. If one looks at how the Herschel project has been handled, or even some big NASA projects, data acquisition is planned out years in advance, data are divvied up in ways that make political but not scientific sense (e.g. person A will work on region A, and person B on region B), and key insights (e.g. from combining and contrasting "A" and "B") are either delayed or lost altogether. If the US retreats farther from the world of "risk-tolerant" science, which requires a comprehensive suite of facilities to be available to researchers--not just Mega-facilities on their own--the damage may well be irreversible.

• Alberto Bolatto, Assistant Professor, University of Maryland

  Posted on: October 12, 2012

  Closing productive facilities with unique capabilities, such the GBT or the VLBA, is simply not the way of "Advancing Astronomy in the Coming Decade". Or in any decade. The statement that the GBT can be replaced by a combination of Arecibo and Effelsberg, in particular, can only be borne out of technical and practical ignorance: there are reasons why the GBT is off-axis and fully steerable, and with an aperture efficiency of 5% at 3 mm Effelsberg does not approach the capabilities of the GBT at the higher frequencies. This is not to say that better efforts should not have been made to enlarge the respective communities of these instruments, but certainly the NSF will not help that by following the recommendations of the PRC. These recommendations also destroy the support for the training instruments for the next generation of radio astronomers: the University Radio Observatories. As they gut the national open access to small and midsize optical telescopes used to train students. In the end, all US astronomers should take pride in the fact that radio is a wavelength regime where the US leads, technically and scientifically. NRAO is the leading radio astronomical observatory in the world, and it makes available to the US community (and to the entire world, through the open skies policy) top notch, first rate facilities. What we need is stronger funding for basic science, not to destroy the best of what we have in search of funding for the next great thing.

• Francesco Massaro, Postdoctoral Research, Stanford University

  Posted on: October 12, 2012

  The whole astronomical community got unprecedented advantages from the research conducted with the VLBA in every field at every scale. As for example improving our knowledge on astrophysical jets, black holes and their evolution, gamma-ray bursts, distance scales, and stellar evolution to name just a few cases. It is an unique and powerful facility capable of many more exciting discoveries. Closing the VLBA would severely decrease the resources available not only for the US astronomers and but also the entire the astronomical community in the world. In the future years, closing the VLBA facility would be definitively recorded as one of the biggest mistake of the past astronomy, if occurs. I urge the NSF to continue partial support of the VLBA.

• Simon Dicker, Dr, University of Pennsylvania

  Posted on: October 12, 2012

  The AACD report fails to consider the full range of science carried out with the GBT. Even with the limited cases that were considered, the report concluded that the GBT was the best instrument of its type but that radio astronomers would have to "make do" with lesser instruments. In fact for many projects - for example those using large focal plane arrays at higher frequencies - there are no other instruments to "make do" on.

• Jonathan McDowell, Dr, SAO

  Posted on: October 12, 2012

  Closing facilities like GBT and VLBA is foolish. If the budget is tight, don't put money into the most expensive new projects at the expense of a wide portfolio of cheaper facilities. Astronomy is stronger for its ability to support a mix of small and large research endeavours. It's the large projects that must wait for better financial times.

• Jonathan Sievers, Research Scholar, Princeton University

  Posted on: October 12, 2012

  The GBT has irreplaceable capabilities. With multi-pixel arrays, particularly at higher frequencies, it could be up to an order of magnitude faster than other facilities and a small fraction of the cost. To have skimped on instrumentation, and then to effectively use that as an excuse to close the facility is backwards logic.

• Hiroshi Imai, Associate professor, Kagoshima University

  Posted on: October 12, 2012

  These are the summary of my concerns about the VLBA and GBT in the Portfolio Review Committee (PRC) report; some of them appear in the NRAO Users Committee Letter. 1) Lifetime of high-tech astronomical instruments World-leading radio telescopes may have been a typical instrumental and scientific lifetime of 30 years without any fatal instrumental and scientific breakdown followed by update/repair just for its recovery. For example, the EVLA project looks a renewal/reborn rather than just regular update. The old VLA lasted for about 30 years, consistent with the typical lifetime mentioned above. When US people talk about the glorious history of astronomy (not just radio astronomy), the commissioning periods of the GBT and the VLBA should be an important factor in the history. Too early closure of the GBT and the VLBA with the commissioning periods of only 14 and 24 years in 2017, especially soon after the major investment as already pointed out, may be a blemish on the history. Moreover, the oversubscription rates of the machine time of GBT and the VLBA are not only healthy values at moment, rather increasing. This implies that, although promising proposals are effectively selected, some opportunity of hidden amazing discovery in the rejected proposals will be lost. The GBT and the VLBA need longer lifetime to spend their machine time for wider field of astronomy. Thus the lifetime of the GBT and the VLBA should be reevaluated. 2) International alliance to support/encourage US radio astronomy The users communities of other facilities are also strong supporters of the GBT and the VLBA and eager to experience the world-class science with the GBT and the VLBA until they can do such science with their own facilities. In fact, we have seen such an example in the VLBA in which some communities financially support the VLBA although they have their own facilities. If NRAO facilities are really flagships of radio astronomy as phrased for a long time, they need "fleet" in the international community. Immediate missing of the GBT and the VLBA means missing such a fleet and causes devolution of the fields led by the GBT and the VLBA. As already mentioned, long operations of the GBT and the VLBA should be more cost efficient than decommission for the international radio astronomical community. Otherwise each region has to pay more financial, time, and human costs for constructing their own facilities. Even in the worst case, renunciation of the open sky policy is much better than complete loss of the GBT and the VLBA. I have heard of opportunity requirement of financial contributions from small institutes and universities in non-US countries. Although proposal selections should be highly scientifically oriented, it may be helpful for telescope operation. Alternatively, any human contribution such as Resident/Open Risk Shared Programs can be effectively operated. In any case, the NFS contribution is still necessary to maintain the GBT and the VLBA themselves. The PRC report should recommend such a new business models rather than just decommission without any future portfolio strategy. Moreover, the PRC report does not fairly look at some of the current and forthcoming facilities in the world, such as SKA precursors and Chinese FAST, which seems to cause some misjudging of the priorities and the portfolio plan of the GBT and the VLBA. It is true that all of NRAO facilities are now leading world-class science and unreplaceable in the coming decade and longer. Even if other projects are not so good as the GBT and the VLBA now, they aim to share scientific contributions to currently attractive science. After these new facilities start regular operation, this should be the reasonable epoch of decommission of the GBT and the VLBA in order to focus on new adventure. However, it takes so long time to achieve such conditions and further investment in these projects is necessary. Continuous operations of the VLBA and GBT even without further major investment are still indispensable. 3) Plans for construction of future US-led facilities It is really essential to carefully consider a possible transition from existing and future generation facilities of US radio astronomy. Firstly, this should persist to cover the whole wavelength bands highly available at present (from meter to submillimeter). It is because the New World New Horizon (NWNH) goals logically demand integrated efforts and achievements in such wide wavelength bands. Secondly, the transition also should provide health of accessibility to decadal world-class facilities currently maintained by NRAO for next generation astronomers in US. They will lead the NWNH goals with the new facilities, but they can still be trained more effectively with the existing facilities rather than those that are highly prioritized by the PRC report, such as CCAT, but whose scientific and educational operation models are still fuzzy and now being planned. The facility transition also should consider based on scientific and budgetary economics. GBT and the VLBA nowadays have best cost-performance in the world based on health of maintenance by NRAO and fresh capability of low-cost and high performance signal receiving and processing systems. If the PRC report supposes a pessimistic portfolio scenario, I still favor GBT and the VLBA over fast commissioning of the new facilities because the formers may have higher cost performance and it is much better to waiting for the new facilities whose commission will be delayed rather than divesting the health of radio astronomy in the forthcoming decade. In fact, especially the VLBA is partially supported by international and non-NFS funds, keeping good telescope maintenance and operation as well as the open sky policy within which US community can access to the VLBA and lead some Key Projects pushing the NWNH goals. I will encourage promotion of the new facilities after reasonably and efficiently scientific, educational, and budgetary models are presented to the community.

• Greg Taylor, Associate Professor, UNM

  Posted on: October 12, 2012

  Closing the VLBA would be a terrible mistake. The VLBA is a unique and powerful instrument that has improved substantially since the New Worlds New Horizons report on which the 2012 Portfolio Revew Report is based. The VLBA provides the astronomical community with its highest resolution which has been of fundamental importance to understanding the nature of astrophysical jets, black holes and their evolution, gamma-ray bursts, distance scales, and stellar evolution to name just a few areas. I have advised four PhD students and one MS student who used the VLBA as the primary facility for their thesis research. I have used the VLBA in numerous classes to inspire students, both graduate and undergraduates. It is an amazing instrument capable of many more exciting discoveries. Given its broad applicability (to plate tectonics and spacecraft navigation as well as astrophysics) it is reasonable to seek partial support from numerous disciplines as recommended by the 2006 Portfolio Review. But closing this unique and powerful facility would severely diminish the resources of the US astronomical community and the world. I urge the NSF to continue partial support of the VLBA.

• Sarah B Spolaor, Dr., Jet Propulsion Laboratory, California Institute of Technology

  Posted on: October 11, 2012

  I will input a word on high-resolution radio astronomy and the VLBA. The VLBA is a unique facility not only in the USA, but worldwide: its world-class mix of flexibility, consistency of data quality, and unmatched sensitivity and angular resolution, make it distinctive among its (few) peers, and a unique stronghold of U.S. astronomy. It furthermore provides cutting-edge prospects in extragalactic astronomy. The VLBA is able to directly (and quickly) image sub-parsec scales in distant galaxies, exploring radio jet phenomena near supermassive black holes, and allowing the capability to track movements of binary black hole systems, or jets related to such systems, down to orbital scales where the systems may be gravitational-wave emitters. The VLBA also recently began supporting a highly promising commensal search for fast radio transients (V-Fastr), which is the only current system capable of identifying an extragalactic pulse, then precisely localizing its host. This capability, when an extragalactic pulse population is detected through it, will provide a groundbreaking cosmological exploration tool. As such a population seems to exist (Thornton et al, in prep), it seems that V-Fastr detections are likely only a matter of time. Before the advent of the Square Kilometre Array, and possibly even after, the ability to efficiently perform such studies may be irreparably hurt with a loss or significant downgrade of VLBA operations.

• Ue-Li Pen, Professor, CITA

  Posted on: October 11, 2012

  I found the key logic for closing GBT bizarre: that Arecibo and Effelsberg provide some level of overlapping capability. I could think of some 8 meter (not to mention smaller ones) optical telescopes which by this argument would be much more redundant. To say that the US community should give up its lead in pulsar timing to offshore competitors is almost insulting, in a field that has earned two Nobel prizes, and may well earn another one for gravitational wave detection.

• Jun-ichi Nakashima, Research Assistant Professor, The University of Hong Kong

  Posted on: October 10, 2012

  VLBA and GBT have served as the backbone of postgraduate education not only in US but also across the globe, in particular, in countries/regions, in which no major telescope projects exist. One of my students in Hong Kong never accomplished his dissertation work without VLBA and GBT. The significance of existence of these telescopes is more than just scientific values.

• Stacy McGaugh, Professor, Case Western Reserve University

  Posted on: October 10, 2012

  The GBT is an incredible flexible as well as powerful radio telescope. To give but one example, it is making new discoveries in the Local Group that completely surprised me. It is a relatively new facility with new instruments still coming on-line. It seems very odd to suggest closing the GBT at this time.

• Deidre Hunter, Astronomer with Tenure, Deputy Director of Science, Lowell Observatory

  Posted on: October 10, 2012

  Closing the GBT would be silly. It is the premiere instrument of its kind in the world and it is just hitting its stride now. It is doing science that no other instrument in the world can do---not Effelsberg, not Arecibo.

• Maura McLaughlin, Associate Professor, West Virginia University

  Posted on: October 9, 2012

  The NANOGrav collaboration's response to the Portfolio Review can be found on our website (http://nanograv.org). In summary, the pulsar timing approach to gravitational wave detection uniquely probes waves at nanohertz frequencies along with non-linear bursts from inspiraling black holes. It is therefore a critical capability with its own discovery space and potential. The GBT is crucial to our efforts in two important ways. New spin-stable millisecond pulsars (MSPs) found in large surveys will greatly increase sensitivity. The GBT's wide sky coverage is crucial for finding MSPs in underpopulated regions of the sky. Secondly, the pulsar timing program requires a broad range of frequencies, sensitivity, observing cadences, and sky coverage that only Arecibo and the GBT together can provide. The Jansky Very Large Array (JVLA) can play a supporting role in the overall pulsar program but cannot replace the GBT for either pulsar surveys or for long-term, multi-frequency timing with high cadence. Furthermore, the GBT is the only 100-meter class telescope in a radio-quiet zone. Other telescopes (Effelsberg, Lovell, Nancay, Parkes, Sardinia) are also less capable than the GBT in one or more additional aspects crucial for pulsar work.

• Mark Reid, Senior Astronomer, Harvard-Smithsonian CfA

  Posted on: October 2, 2012

  If the portfolio review recommendations are enacted, it would close 2 of the 5 major US radio facilities. It would scrap a recent NSF investment of order $200M. This would effectively drive a stake through the heart of radio astronomy in the U.S.

• Jay Strader, Assistant Professor, Michigan State University

  Posted on: September 24, 2012

  Both the portfolio review and responses to it still underestimate the role of the GBT in pulsar science. A large fraction of interesting pulsars are found in globular clusters, where they are dynamically formed, not in the general field. Globular clusters are concentrated toward the center of our Galaxy, which is located in the south. Because of its declination limits, Arecibo cannot ever study these clusters. Only a few can be reached by Effelsberg, and then only for 1-2 hours per night. It is foolish to just compare the sky area when comparing telescopes: not all parts of the sky are equal, and without the GBT we won't be able to study one of the most interesting parts.

• Michael Busch, Jansky Fellow, National Radio Astronomy Observatory

  Posted on: September 24, 2012

  The portfolio review omits mention of much of the planetary science done with the GBT and VLBA. The GBT is used for detailed observations of comets; for bistatic radar observations of nearby and fast-rotating near-Earth asteroids with Arecibo (most recently 2012 QG42 during the 3rd week of September); and for radar speckle tracking observations of Mercury, Venus, Ganymede, and Europa in conjunction with the 70-m antenna at Goldstone. The Europa speckle tracking is particularly notable because it may yield a measurement of the thickness of the ice shell, essential for planning future Europa missions. For the last four years, I have used the VLBA for speckle tracking observations of near-Earth asteroids in conjunction with Arecibo, to determine their spin states. This allows us to construct shape models of those objects and to improve trajectory predictions - either for spacecraft or for potential Earth impacts. Several of our targets are now or are being considered as spacecraft targets, most notably Toutatis, which the Chang'e 2 spacecraft will fly by this December.