Home | AAS 241 Special Session — New Windows onto the Universe with the GBT: Asteroids, Exotic Stars, Gaseous Filaments and More

AAS 241 Special Session — New Windows onto the Universe with the GBT: Asteroids, Exotic Stars, Gaseous Filaments and More

Monday, January 9th, 2023 from 2-3:30 pm (PST) – Room 605/610

Poster sessions highlighted during the Monday morning break (9 am PST)

Join us at our Special Session at the Seattle AAS. Hear from scientists including Steve Croft, Thankful Cromartie, Simon Dicker, Rachel Friesen, Anika Schmiedeke, Kristine Spekkens, and Patrick Taylor!

The GBT’s 100-meter unblocked aperture, active surface, and 0.3-116 GHz frequency coverage makes it one of the most sensitive and flexible astronomy instruments in the world. Having already made history with its myriad of discoveries, the GBT will be vital to the goals and aspirations of the next decades. New instrumentation will be vital to ensure scientists worldwide will be able to maximize the GBT’s potential and meet the aspirational goals described in Pathways to Discovery and Origins, Worlds, and Discovery, the most recent decadal plans for astrophysics. In this session we look at five areas of scientific research which would benefit from new instrumentation – the discovery and study of exotic stellar objects, detection of diffuse inter-galaxy gas, understanding star formation from sub-pc to kpc scales (including at exceptionally low gas densities), understanding the origin, dynamics, and interiors of solar system objects, and the detection of technosignatures. Here we will discuss the current state and future discoveries in these fields and discuss the role the GBT will have in these discoveries. The session will end with a panel discussion looking at the merits of new instruments for the GBT and the prioritization of these instruments. 

This Special Session features 7 invited oral presentations as well as contributed iPoster presentations. The oral program and posters appear below (click on titles to see the full abstract).

Oral Presentations

Monday, January 9 from 2 – 3:30 pm (PT) – Room 605/610

Kristine Spekkens – Royal Military College / Queen’s University, Kingston, ON, Canada

A variety of observations and simulations imply the existence of diffuse, low column density HI reservoirs in and around nearby galaxies which are hundreds of times fainter than the emission from their HI disks. Mapping diffuse HI requires both high sensitivity and high dynamic range over wide fields of view, a combination that is out of reach for most facilities but which ALPACA on the GBT will be very well-suited to deliver. This talk will present an overview of the science case for mapping diffuse HI in the local universe and the discuss future prospects for ALPACA on the GBT in this field.

Steve Croft – UC Berkeley, Berkeley, CA

The Green Bank Telescope has been one of the primary facilities for technosignature searches since 2016, as part of the Breakthrough Listen (BL) initiative. BL has deployed one of the world’s most capable digital spectrometers to the GBT, capable of digitizing billions of frequency channels simultaneously. This backend routinely operates with many of the existing feeds at GBT and can be configured quite easily to operate with new instruments.

As noted in the Decadal Review, “It is humbling and exciting to contemplate that the question of whether life exists elsewhere could be answered with the technology humanity now possesses.” The GBT is already providing some of the strongest constraints to date on the existence of technologically-capable extraterrestrial life, and the deployment of new capabilities at GBT providing increased coverage in both instantaneous bandwidth and sky coverage promise to accelerate the search further.

The BL backend, as well as data from the public BL archive, are also being used for RFI characterization, axion dark matter searches, and studies of fast radio bursts, and we look forward to further collaborations with the broader radio astronomy community as well as those interested in seeking the answer to the most profound question in astronomy: Are we alone?

Anika Schmiedeke – Green Bank Observatory, Green Bank, WV

In this talk, I will outline science opportunities achievable with Argus144, a planned 144-element receiver array for spectroscopic studies in the 3 mm W-band (74-116 GHz) to be installed on the Green Bank Telescope (GBT). The 6’x6′ field of view combined with a ~8″ beam will provide high spatial dynamic range maps of interstellar molecules that are crucial in understanding the physical, kinematic, and astrochemical processes associated with star formation from galactic disc scales to the sub-parsec scale of interstellar filaments and dense molecular cloud cores.

Argus144 on the GBT will be an unmatched instrument for large-area, high-resolution studies of molecular gas. It will be an excellent complement to 3mm studies with ALMA, which has a higher spatial resolution, but a much smaller field of view.

Patrick Taylor – National Radio Astronomy Observatory, Green Bank Observatory, Charlottesville, VA

For over 20 years, the 100-m Green Bank Telescope (GBT) has served as a highly sensitive receiver for bistatic radar observations to dynamically and physically characterize near-Earth objects, the Moon, the terrestrial planets, and the Galilean satellites of Jupiter. However, until recently, the Green Bank Telescope had never been used as a radar transmitter. The National Radio Astronomy Observatory (NRAO), Green Bank Observatory (GBO), and Raytheon Intelligence & Space (RIS) are designing a high-power, next generation planetary radar system (ngRADAR) for the GBT at GBO. As a pilot project, a low-power, Ku-band transmitter (up to 700 W at 13.9 GHz) designed by RIS was integrated on the GBT, and radar echoes were received at NRAO’s ten 25-meter Very Long Baseline Array (VLBA) antennas. These observations generated the highest-resolution, ground-based images of the Moon ever collected, provided physical characterization of space debris, and detected a near-Earth asteroid at a distance of 2.1 billion meters (~5.5 lunar distances) from Earth. Pilot observations demonstrated the capability of obtaining meter-scale radar imagery of the lunar surface, while a high-power system would have nearly 1000 times the output power and several times the waveform bandwidth (up to 600 MHz) allowing for even more sensitivity and finer resolution. These properties will deliver a highly capable radar system for astrometry, imaging, and physical and dynamical characterization of solar system objects for planetary science and planetary defense as well as for space situational awareness in the cislunar domain.

The ngRADAR system could also be used in conjunction with the future Next Generation Very Large Array (ngVLA) to greatly enhance receiver sensitivity. The recent decadal survey Origins, Worlds, and Life: A Decadal Strategy for Planetary Science and Astrobiology 2023-2032 strongly endorsed planetary radar facilities, recommending planning for ground-based, planetary radar capabilities comparable to or exceeding those of the Arecibo Observatory, the use of existing infrastructure for planetary radar, and development and maturation of radar technologies. The ngRADAR project is well-positioned to respond to the recommendations of the planetary science decadal survey by utilizing the existing telescope infrastructure of the GBT and the VLBA, along with the potential to leverage future infrastructure such as the ngVLA, as well as developing novel technology and techniques for use in planetary radar.

Rachel Friesen – University of Toronto, Toronto, ON, Canada

Molecular clouds, the birthplaces of stars, are highly structured and filamentary. Wide-field continuum surveys in the Galaxy have shown clearly that ongoing star formation is strongly correlated with dense molecular filaments, both for low mass stars that preferentially form within filaments, and for higher mass stars where the intersection of filaments create stellar cluster-forming ‘hubs’ and massive, dense molecular ridges. With the 7-pixel K-band Focal Plane Array, multiple Large Programs targeting emission from ammonia (NH3) have provided the critical kinematic counterpoint to these continuum surveys in a variety of environments, from the Gould Belt to the Galactic Plane. I will introduce these surveys’ impacts on our understanding of the stability of filaments and cores, gas kinematics and flows within filaments, and mass accretion in the early stages of star formation. Looking to the future, I will then discuss how the proposed K-band Phased Array Feed (KPAF) on the GBT will answer outstanding questions about the formation and evolution of star-forming filaments and cores. In particular, the KPAF will enable both wider-field and deeper molecular line surveys of the Galaxy than is currently possible with the KFPA, or other facilities. Lastly, I will highlight the powerful combination of observations with the KPAF and the ngVLA for star formation studies.

Simon Dicker 1, Mark Devlin 2, Bradley Johnson 3, Brian Mason 4, Philip Mauskopf 5, Emily Moravec 6, Tony Mroczkowski 7, Charles Romero 8, Jonathan Sievers 9

1 University of Pennsylvania, Philadelphia, PA, 2 Univ. of Pennsylvania, Philadelphia, PA, 3 University of Virginia, New York, NY, 4 NRAO, Charlottesville, VA, 5 Arizona State University, Tempe, AZ, 6 Green Bank Observatory, Arbovale, WV, 7 ESO, Garching bei München, Germany, 8 Center for Astrophysics, Middle River, MD, 9 McGill University, Montreal, QC, Canada

The MUSTANG2 bolometer camera on the Green Bank Telescope (GBT) offers a 4.2′ diameter field-of-view (fov) with a diffraction limited resolution of 9″ and a wide 75-105 GHz band. Noise levels of 56 µJy/beam over a 4′ diameter region are reached in one hour enabling a wide range of science. Highlights include follow-up observations of galaxy clusters, star forming cores, surveys of the Galactic plane, and probing the surface of the Moon at 16 km resolution. However, MUSTANG2 uses less than half of the available 90 GHz fov of the GBT and is not sensitive to polarization.

Since MUSTANG2 was built, advances in instrumentation mean that a polarization sensitive camera with an 8.5′ diameter fov and over 19 times the mapping speed could be built using existing technology. The greater mapping speed would make better use of valuable high frequency observing time, while the larger fov would enable maps with high fidelity on angular scales up to those of the Planck satellite. Improved readout electronics allows thousands of detectors to be read out with low cost components. This order of magnitude higher detector count enables additional sensitivity increases by closer detector spacing (1 f-lambda instead of 2 f-lambda).

Our proposed new wide-field camera for the GBT will have several differences from MUSTANG2. By switching to 100 mK cryogenics (instead of 300 mK) it is possible to use MKID detectors which are far easier to manufacture. These will have low enough noise that users who do not require polarization can co-add the polarizations with little to no noise penalty than if the detectors were unpolarized. The 100 mK base temperature and highly multiplexed readout means that the instrument could also be upgraded to include multiple frequency bands and produce instantaneous spectra over a frequency range and at a sensitivity few telescopes can match. As well as allowing the GBT to carry out its existing science program better and faster, maps with sub-microkelvin noise will be made using reasonable integration times, opening new frontiers such as the study of groups of galaxies at redshifts greater than 3.

Thankful Cromartie — Cornell University

Over the last twenty years, the Green Bank Telescope has distinguished itself as a world-class instrument for studying the most exotic compact objects in the Universe. I will discuss the exciting science — including millisecond pulsar discoveries, subsequent tests of general relativity, high-precision pulsar timing for gravitational wave detection, and constraints on the neutron star equation of state — that was made possible only through the powerful capabilities of the GBT. I will then discuss how the forthcoming Ultra-Wideband Receiver and ALPACA phased-array feed will further revolutionize science in these areas.

Poster Presentations

Monday, January 9 from 9 – 10 am – Exhibit Hall

Ryan Lynch1, Steve White1, Bob Simon1, Scott Ransom2, Paul Marganian1, Joe Brandt1, Dennis Egan1, Ramon Creager1, Dane Sizemore1, Laura Jensen1,3, Art Symmes3 
1Green Bank Observatory, Green Bank, WV, 2NRAO, Charlottesville, VA, 3National Radio Astronomy Observatory, Charlottesville, VA

Poster Link: https://aas241-aas.ipostersessions.com/Default.aspx?s=aas_241_gallery

We present commissioning results for the 0.7 – 4 GHz ultra-wideband receiver (UWBR) that has been built for the Robert C. Byrd Green Bank Telescope (GBT). The primary science driver for the new receiver is improving sensitivity to nanohertz-frequency gravitational waves (as well as other areas of fundamental physics and astrophysics) via high-precision timing of millisecond pulsars. The UWBR frequency range is optimized for measuring and mitigating interstellar medium effects that act as a noise source in pulsar timing. UWBR will also enable wide-band studies of fast radio bursts, magnetars, and other fast radio transients, and will be useful for astrochemistry and observations of radio recombination lines, especially in the 3-4 GHz range (where the GBT does not currently operate). We will present measurements of the system noise and sensitivity, polarization characteristics, and continuum stability. We will also show results from early observations of key millisecond pulsars, star forming regions, and distant galaxies. Finally, we will discuss plans for early science operations with UWBR.

Ronald Maddalena, David Frayer, Emily Moravec, Pedro Salas, Anika Schmiedeke, Ellie White – Green Bank Observatory, Green Bank, WV

Poster Link: https://aas241-aas.ipostersessions.com/?s=C6-9D-58-C4-DD-D8-D7-7C-1B-7C-42-C7-48-68-21-BD

The Green Bank Telescope has an active surface, 100 m in diameter, that can provide a surface accuracy of 230 μm, which is sufficient for observing at wavelengths as short as 2.6 mm. Obtaining such a high surface accuracy requires compensating for gravitational structural deformations over the telescope’s 5° to 90° range of elevation as well as differential thermal deformations. The telescope uses a look-up table for the repeatable gravitational deformations and a thermal model that employs multiple temperature sensors to correct the pointing and focus of the telescope. In addition, for high-order thermal aberrations like coma and astigmatism, observers periodically perform an out-of-focus holography measurement (e.g., Nikolic et al., 2007, A&A, 465, 685-693) of a bright point source, the results of which are automatically applied to the telescope surface as coefficients to 5th order Zernike polynomials. Since the time scale for thermal changes during the day is comparable to the time needed for out-of-focus holography, high-frequency observations are currently scheduled only at night.

We are in the process of testing what we believe is a faster technique than out-of-focus holography for correcting thermal aberrations, which might make practical daytime observing at high frequencies. The software points the telescope at a moderately-bright continuum source and alters the coefficient for a single Zernike polynomial to determine the value that produces the maximum gain. The software then repeats these measurements as it steps through the subset of Zernike polynomials known to be sensitive to thermal changes. Once all coefficients are automatically adjusted, the software repeats the process until the measured gain is maximized. Simulations suggest that, during the day and under atmospheric opacity and wind conditions suitable for high-frequency observing, the whole process converges in less than half the time of a holography observation. Unlike holography, the software determines beforehand if weather conditions and the chosen astronomical source are suitable and reports at every step the improvement in telescope gain.

Will Armentrout, Brenne Gregory, Sue Ann Heatherly, Dane Sizemore, Kathlyn Purcell, Madge Vosteen – Green Bank Observatory, Green Bank, WV

Daniel Reichart – University of North Carolina at Chapel Hill, Chapel Hill, NC

Poster Link: https://aas241-aas.ipostersessions.com/?s=71-1C-6E-9E-50-0C-4B-AF-71-00-ED-9B-2B-1F-93-8B

The 20-meter telescope at the Green Bank Observatory is a fully remote-controlled telescope that enables you and your students to easily become familiar with radio astronomy science and observations. We use an online queue-based system (Skynet) that allows you to submit observations and have them automatically observed when the source is visible. Your observations will be calibrated and available to you within minutes of the observation. Currently, we have supported modes for spectral line (HI, OH, recombination lines, etc), continuum, and pulsar observations, including mapping or pointed observations. We offer a range of free educational programs for groups using the 20-meter, including virtual “Radio Astronomer for a Day” and “Milky Way Discovery” programs, in-person visits, and Skynet Junior Scholars. We also offer telescope time contracts for research programs and astronomy classes. These are an ideal complement to optical astronomy labs in introductory courses. We mainly operate between 1.3-1.8 GHz, but an 8-10 GHz receiver is also available on a limited basis.

In addition to these educational opportunities, the 20-meter is a powerful tool for triggered, time-variable (pulsar, FRB, etc.), and satellite observations. We expect a response time of as little as 30 seconds for triggered observations, time resolution down to 0.1 ms, frequency resolution under 1 kHz, continuum confusion limit of 1.3 Jy/beam, and line sensitivity of 20 mJy in one hour (with 10 km/s channels).

Karen O’Neil, William Armentrout, Jesse Bublitz, David Frayer, Brenne Gregory, James Jackson, Felix Lockman, Ryan Lynch, Anthony Minter, Emily Moravec, Lawrence Morgan, Pedro Salas, Anika Schmiedeke, Andrew Seymour, Evan Smith – Green Bank Observatory, Green Bank, WV

Poster Link: https://aas241-aas.ipostersessions.com/?s=6E-A1-EE-DF-60-9D-7F-A1-AF-7B-E9-36-B8-B9-B0-98

The Green Bank Telescope (GBT) is a unique resource for the US and global research community. The combination of its fully steerable 100-meter unblocked aperture, active surface, 0.29-116 GHz frequency coverage, flexible instrumentation, and location in two different interference protection zones are not found in any other telescope. It is the world’s premier telescope for studying low-frequency gravitational waves, multi-messenger astronomy, fundamental physics, fast radio transients, cosmology, star formation, astrochemistry, gas in galaxies, and in the search for technosignatures.

The GBT’s 100-meter diameter unblocked primary reflector has an active surface that can maintain an RMS surface accuracy of 230μm under stable thermal conditions. This surface accuracy yields good observing efficiency at frequencies as high as 116 GHz. The unblocked aperture produces an extremely clean point spread function and resulting data with a high dynamic range. The GBT can observe declinations as low as -47, covering 85% of the entire celestial sphere. Green Bank has approximately 2,000 hours per year with atmospheric opacity suitable for observing at 70-116 GHz and near the 22 GHz water line, and the GBT is scheduled dynamically to take full advantage of these conditions.

The GBT’s suite of low-noise radio receivers provides nearly continuous frequency coverage from 0.29-116 GHz, and its spectrometer can process as much as 4-8 GHz of instantaneous bandwidth. The GBT current instrument suite includes several multi-pixel receivers: the K-Band 7-pixel Focal Plane Array, the Argus 16-pixel receiver, and the MUSTANG2 90 GHz 223-pixel bolometer array.

Here we discuss the GBT’s current capabilities and describe planned and potential new instrumentation.

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