The active reflector of FAST(five-hundred-meter aperture spherical radio telescope) is supported ... more The active reflector of FAST(five-hundred-meter aperture spherical radio telescope) is supported by a ring beam and a cable-net structure,in which nodes are actively controlled to form series of real-time paraboloids.To ensure the security and stability of the supporting structure,tension must be monitored for some typical cables.Considering the stringent requirements in accuracy and longterm stability,magnetic flux sensor,vibrating wire strain gauge and fiber bragg grating strain gauge are screened for the cable tension monitoring of the supporting cable-net.Specifically,receivers of radio telescopes have strict restriction on electro magnetic interference(EMI) or radio frequency interference(RFI).These three types of sensors are evaluated from the view of EMI/RFI.Firstly,these fundamentals are theoretically analyzed.Secondly,typical sensor signals are collected in the time and analyzed in the frequency domain,which shows the characteristic in the frequency domain.Finally,typical sensors are tested in an anechoic chamber to get the EMI levels.Theoretical analysis shows that Fiber Bragg Grating strain gauge itself will not lead to EMI/RFI.According to GJB151 A,frequency domain analysis and test results show that for the vibrating wire strain gauge and magnetic flux sensor themselves,testable EMI/RFI levels are typically below the background noise of the anechoic chamber.FAST finally choses these three sensors as the monitoring sensors of its cable tension.The proposed study is also a reference to the monitoring equipment selection of other radio telescopes and large structures.
We present deep CCS and HC 7 N observations of the L1495-B218 filaments in the Taurus molecular c... more We present deep CCS and HC 7 N observations of the L1495-B218 filaments in the Taurus molecular cloud obtained using the K-band focal plane array on the 100m Green Bank Telescope. We observed the L1495-B218 filaments in CCS J N = 2 1 −1 0 and HC 7 N J = 21−20 with a spectral resolution of 0.038 km s −1 and an angular resolution of 31. We observed strong CCS emission in both evolved and young regions and weak emission in two evolved regions. HC 7 N emission is observed only in L1495A-N and L1521D. We find that CCS and HC 7 N intensity peaks do not coincide with NH 3 or dust continuum intensity peaks. We also find that the fractional abundance of CCS does not show a clear correlation with the dynamical evolutionary stage of dense cores. Our findings and chemical modeling indicate that the fractional abundances of CCS and HC 7 N are sensitive to the initial gas-phase C/O ratio, and they are good tracers of young condensed gas only when the initial C/O is close to solar value. Kinematic analysis using multiple lines including NH 3 , HC 7 N, CCS, CO, HCN, & HCO + suggests that there may be three different star formation modes in the L1495-B218 filaments. At the hub of the filaments, L1495A/B7N has formed a stellar cluster with large-scale inward flows (fast mode), while L1521D, a core embedded in a filament, is slowly contracting due to its self-gravity (slow mode). There is also one isolated core that appears to be marginally stable and may undergo quasi-static evolution (isolated mode).
MUSTANG-2 is a 90 GHz feedhorn-coupled, microwave SQUID-multiplexed TES bolometer array in the fi... more MUSTANG-2 is a 90 GHz feedhorn-coupled, microwave SQUID-multiplexed TES bolometer array in the final stages of development for operation on the 100-m Robert C. Byrd Green Bank Telescope. We present the camera design and report the performance during the first season of observation, in which 64 of the available 215 pixels in the focal plane were populated. We highlight the microwave multiplexing readout technology, which is envisioned as a path to read out the next generation of large pixel-count cryogenic focal planes. In this regard, MUSTANG2 is a pathfinder for this multiplexing technology. We present noise spectra which show no detector noise degradation when read out with microwave SQUID multiplexing, and we present first light images of Jupiter and M87, which demonstrate the end-to-end system performance.
MUSTANG 2 is a 223 element focal plane that operates between 75 and 105 GHz on the 100 meter Gree... more MUSTANG 2 is a 223 element focal plane that operates between 75 and 105 GHz on the 100 meter Green Bank Telescope. It shares many of the science goals of its predecessor, MUSTANG, but will have fifteen times the sensitivity and five times the field-of-view. Angular scales from 900 to 60 will be recovered with high fidelity providing a unique overlap between high resolution instruments such as ALMA and lower resolution single dish telescopes such as ACT or SPT. Individual TES bolometers are placed behind feedhorns spaced by 1.9λ f and are read out using a microwave SQUID multiplexing system.
American Astronomical Society Meeting Abstracts, Jan 11, 2021
To carry out astronomical observations in the molecule rich 3 mm window the Green Bank Telescope ... more To carry out astronomical observations in the molecule rich 3 mm window the Green Bank Telescope (GBT) compensates for gravitational and weather induced deformations of its primary reflector. Terrestrial laser scanners (TLSs) offer a fast and reliable means of measuring these deformations, but their use has been limited to measuring gravitational deformations thus far due to the large systematics inherent to their construction. The laser antenna surface scanning instrument (LASSI) on the GBT uses a TLS to measure weather induced deformations. The LASSI removes the TLS systematics by taking the difference between scans. We use the active surface (AS) on the GBT to validate this strategy and find that the LASSI can accurately measure deformations corresponding to different Zernike polynomials with amplitudes between 60 μm and 550 μm. We estimate that the wavefront error introduced by the LASSI to the surface is 100 ± 30 μm, root-mean-squared (rms), which would result in a total surface error of 250 μm rms. This suggests that using the LASSI to measure, and the AS to correct, for weather induced deformations is a viable method to efficiently carry-out day time 3 mm observations with the GBT.
The Hydrogen Epoch of Reionization Array (HERA) is a radio interferometer aiming to detect the po... more The Hydrogen Epoch of Reionization Array (HERA) is a radio interferometer aiming to detect the power spectrum of 21 cm fluctuations from neutral hydrogen from the Epoch of Reionization (EOR). Drawing on lessons from the Murchison Widefield Array (MWA) and the Precision Array for Probing the Epoch of Reionization (PAPER), HERA is a hexagonal array of large (14 m diameter) dishes with suspended dipole feeds. Not only does the dish determine overall sensitivity, it affects the observed frequency structure of foregrounds in the interferometer. This is the first of a series of four papers characterizing the frequency and angular response of the dish with simulations and measurements. We focus in this paper on the angular response (i.e., power pattern), which sets the relative weighting between sky regions of high and low delay, and thus, apparent source frequency structure. We measure the angular response at 137 MHz using the ORBCOMM beam mapping system of Neben et al. We measure a colle...
With a 100 m × 110 m off-axis paraboloid dish, the Green Bank Telescope (GBT) is the largest full... more With a 100 m × 110 m off-axis paraboloid dish, the Green Bank Telescope (GBT) is the largest fully steerable radio telescope on Earth. A major challenge facing large ground-based radio telescopes is achieving sufficient pointing accuracy for observing at high frequencies, up to 116 GHz in the case of the GBT. Accurate pointing requires the ability to blindly acquire source locations and perform ad hoc corrections determined by observing nearby calibrator sources in order to obtain a starting position accurate to within a small margin of error of the target’s location. The required pointing accuracy is dependent upon the half-power beamwidth, and for the higher-frequency end of GBT observing, this means that pointing must be accurate to within a few arcseconds RMS. The GBT’s off-axis design is advantageous in that it eliminates blockage of the dish and reduces sidelobe interference, and there is no evidence that the resulting asymmetric structure adversely affects pointing accuracy. ...
We report the design and development of a self-contained multi-band receiver (MBR) system, intend... more We report the design and development of a self-contained multi-band receiver (MBR) system, intended for use with a single large aperture to facilitate sensitive & high time-resolution observations simultaneously in 10 discrete frequency bands sampling a wide spectral span (100-1500 MHz) in a nearly log-periodic fashion. The development of this system was primarily motivated by need for tomographic studies of pulsar polar emission regions. Although the system design is optimized for the primary goal, it is also suited for several other interesting astronomical investigations. The system consists of a dual-polarization multi-band feed (with discrete responses corresponding to the 10 bands pre-selected as relatively RFI-free), a common wide-band RF front-end, and independent back-end receiver chains for the 10 individual sub-bands. The raw voltage time-sequences corresponding to 16 MHz bandwidth each for the two linear polarization channels
2017 United States National Committee of URSI National Radio Science Meeting (USNC-URSI NRSM)
This paper provides a brief overview of the current Green Bank Telescope science program, and an ... more This paper provides a brief overview of the current Green Bank Telescope science program, and an update on technical developments performed since 2010.
We use time-domain electromagnetic simulations to assess the spectral characteristics of the dish... more We use time-domain electromagnetic simulations to assess the spectral characteristics of the dish antenna for the Hydrogen Epoch of Reionization Array (HERA). These simulations are part of a multi-faceted campaign to determine the effectiveness of the dish's design for obtaining a detection of redshifted 21 cm emission from the epoch of reionization. Our simulations show the existence of reflections between HERA's suspended feed and its parabolic dish reflector, at certain frequencies, with an amplitude of roughly $ -35$dB at 100 ns which can lead to some loss of measurable modes and a modest reduction in sensitivity. Even in the presence of this structure, we find that the spectral response of the dish is sufficiently smooth for delay filtering, a proven foreground isolation technique, to contain foreground emission at line-of-sight wave numbers below $k_\parallel \lesssim 0.2h$Mpc$^{-1}$, in the region where the current PAPER experiment operates. Incorporating these result...
To carry out astronomical observations in the molecule rich 3 mm window the Green Bank Telescope ... more To carry out astronomical observations in the molecule rich 3 mm window the Green Bank Telescope (GBT) compensates for gravitational and weather induced deformations of its primary reflector. Terrestrial laser scanners (TLSs) offer a fast and reliable means of measuring these deformations, but their use has been limited to measuring gravitational deformations thus far due to the large systematics inherent to their construction. The laser antenna surface scanning instrument (LASSI) on the GBT uses a TLS to measure weather induced deformations. The LASSI removes the TLS systematics by taking the difference between scans. We use the active surface (AS) on the GBT to validate this strategy and find that the LASSI can accurately measure deformations corresponding to different Zernike polynomials with amplitudes between 60 μm and 550 μm. We estimate that the wavefront error introduced by the LASSI to the surface is 100 ± 30 μm, root-mean-squared (rms), which would result in a total surfac...
The azimuth track of the Green Bank Telescope did not perform as designed. Relative movement of c... more The azimuth track of the Green Bank Telescope did not perform as designed. Relative movement of components was noted during construction; in addition, fretting of the base plate and wear plate faying surfaces, fatigue cracking of the wear plates, fatigue failure of wear plate fasteners, and deterioration of the cementitous grout layer occurred at a rapid pace during the first few years of operation. After extensive failure analysis, a new system of components was designed and fabricated, and installation of the components was performed during 2007 (Symmes, Anderson, and Egan, "Improving the service life of the 100m Green Bank Telescope azimuth track", SPIE 7012-121). The highlights and lessons learned during the fabrication and installation phases are described herein. This information will benefit any organization performing a similar replacement, and may be helpful in new installations as well.
The active reflector of FAST(five-hundred-meter aperture spherical radio telescope) is supported ... more The active reflector of FAST(five-hundred-meter aperture spherical radio telescope) is supported by a ring beam and a cable-net structure,in which nodes are actively controlled to form series of real-time paraboloids.To ensure the security and stability of the supporting structure,tension must be monitored for some typical cables.Considering the stringent requirements in accuracy and longterm stability,magnetic flux sensor,vibrating wire strain gauge and fiber bragg grating strain gauge are screened for the cable tension monitoring of the supporting cable-net.Specifically,receivers of radio telescopes have strict restriction on electro magnetic interference(EMI) or radio frequency interference(RFI).These three types of sensors are evaluated from the view of EMI/RFI.Firstly,these fundamentals are theoretically analyzed.Secondly,typical sensor signals are collected in the time and analyzed in the frequency domain,which shows the characteristic in the frequency domain.Finally,typical sensors are tested in an anechoic chamber to get the EMI levels.Theoretical analysis shows that Fiber Bragg Grating strain gauge itself will not lead to EMI/RFI.According to GJB151 A,frequency domain analysis and test results show that for the vibrating wire strain gauge and magnetic flux sensor themselves,testable EMI/RFI levels are typically below the background noise of the anechoic chamber.FAST finally choses these three sensors as the monitoring sensors of its cable tension.The proposed study is also a reference to the monitoring equipment selection of other radio telescopes and large structures.
We present deep CCS and HC 7 N observations of the L1495-B218 filaments in the Taurus molecular c... more We present deep CCS and HC 7 N observations of the L1495-B218 filaments in the Taurus molecular cloud obtained using the K-band focal plane array on the 100m Green Bank Telescope. We observed the L1495-B218 filaments in CCS J N = 2 1 −1 0 and HC 7 N J = 21−20 with a spectral resolution of 0.038 km s −1 and an angular resolution of 31. We observed strong CCS emission in both evolved and young regions and weak emission in two evolved regions. HC 7 N emission is observed only in L1495A-N and L1521D. We find that CCS and HC 7 N intensity peaks do not coincide with NH 3 or dust continuum intensity peaks. We also find that the fractional abundance of CCS does not show a clear correlation with the dynamical evolutionary stage of dense cores. Our findings and chemical modeling indicate that the fractional abundances of CCS and HC 7 N are sensitive to the initial gas-phase C/O ratio, and they are good tracers of young condensed gas only when the initial C/O is close to solar value. Kinematic analysis using multiple lines including NH 3 , HC 7 N, CCS, CO, HCN, & HCO + suggests that there may be three different star formation modes in the L1495-B218 filaments. At the hub of the filaments, L1495A/B7N has formed a stellar cluster with large-scale inward flows (fast mode), while L1521D, a core embedded in a filament, is slowly contracting due to its self-gravity (slow mode). There is also one isolated core that appears to be marginally stable and may undergo quasi-static evolution (isolated mode).
MUSTANG-2 is a 90 GHz feedhorn-coupled, microwave SQUID-multiplexed TES bolometer array in the fi... more MUSTANG-2 is a 90 GHz feedhorn-coupled, microwave SQUID-multiplexed TES bolometer array in the final stages of development for operation on the 100-m Robert C. Byrd Green Bank Telescope. We present the camera design and report the performance during the first season of observation, in which 64 of the available 215 pixels in the focal plane were populated. We highlight the microwave multiplexing readout technology, which is envisioned as a path to read out the next generation of large pixel-count cryogenic focal planes. In this regard, MUSTANG2 is a pathfinder for this multiplexing technology. We present noise spectra which show no detector noise degradation when read out with microwave SQUID multiplexing, and we present first light images of Jupiter and M87, which demonstrate the end-to-end system performance.
MUSTANG 2 is a 223 element focal plane that operates between 75 and 105 GHz on the 100 meter Gree... more MUSTANG 2 is a 223 element focal plane that operates between 75 and 105 GHz on the 100 meter Green Bank Telescope. It shares many of the science goals of its predecessor, MUSTANG, but will have fifteen times the sensitivity and five times the field-of-view. Angular scales from 900 to 60 will be recovered with high fidelity providing a unique overlap between high resolution instruments such as ALMA and lower resolution single dish telescopes such as ACT or SPT. Individual TES bolometers are placed behind feedhorns spaced by 1.9λ f and are read out using a microwave SQUID multiplexing system.
American Astronomical Society Meeting Abstracts, Jan 11, 2021
To carry out astronomical observations in the molecule rich 3 mm window the Green Bank Telescope ... more To carry out astronomical observations in the molecule rich 3 mm window the Green Bank Telescope (GBT) compensates for gravitational and weather induced deformations of its primary reflector. Terrestrial laser scanners (TLSs) offer a fast and reliable means of measuring these deformations, but their use has been limited to measuring gravitational deformations thus far due to the large systematics inherent to their construction. The laser antenna surface scanning instrument (LASSI) on the GBT uses a TLS to measure weather induced deformations. The LASSI removes the TLS systematics by taking the difference between scans. We use the active surface (AS) on the GBT to validate this strategy and find that the LASSI can accurately measure deformations corresponding to different Zernike polynomials with amplitudes between 60 μm and 550 μm. We estimate that the wavefront error introduced by the LASSI to the surface is 100 ± 30 μm, root-mean-squared (rms), which would result in a total surface error of 250 μm rms. This suggests that using the LASSI to measure, and the AS to correct, for weather induced deformations is a viable method to efficiently carry-out day time 3 mm observations with the GBT.
The Hydrogen Epoch of Reionization Array (HERA) is a radio interferometer aiming to detect the po... more The Hydrogen Epoch of Reionization Array (HERA) is a radio interferometer aiming to detect the power spectrum of 21 cm fluctuations from neutral hydrogen from the Epoch of Reionization (EOR). Drawing on lessons from the Murchison Widefield Array (MWA) and the Precision Array for Probing the Epoch of Reionization (PAPER), HERA is a hexagonal array of large (14 m diameter) dishes with suspended dipole feeds. Not only does the dish determine overall sensitivity, it affects the observed frequency structure of foregrounds in the interferometer. This is the first of a series of four papers characterizing the frequency and angular response of the dish with simulations and measurements. We focus in this paper on the angular response (i.e., power pattern), which sets the relative weighting between sky regions of high and low delay, and thus, apparent source frequency structure. We measure the angular response at 137 MHz using the ORBCOMM beam mapping system of Neben et al. We measure a colle...
With a 100 m × 110 m off-axis paraboloid dish, the Green Bank Telescope (GBT) is the largest full... more With a 100 m × 110 m off-axis paraboloid dish, the Green Bank Telescope (GBT) is the largest fully steerable radio telescope on Earth. A major challenge facing large ground-based radio telescopes is achieving sufficient pointing accuracy for observing at high frequencies, up to 116 GHz in the case of the GBT. Accurate pointing requires the ability to blindly acquire source locations and perform ad hoc corrections determined by observing nearby calibrator sources in order to obtain a starting position accurate to within a small margin of error of the target’s location. The required pointing accuracy is dependent upon the half-power beamwidth, and for the higher-frequency end of GBT observing, this means that pointing must be accurate to within a few arcseconds RMS. The GBT’s off-axis design is advantageous in that it eliminates blockage of the dish and reduces sidelobe interference, and there is no evidence that the resulting asymmetric structure adversely affects pointing accuracy. ...
We report the design and development of a self-contained multi-band receiver (MBR) system, intend... more We report the design and development of a self-contained multi-band receiver (MBR) system, intended for use with a single large aperture to facilitate sensitive & high time-resolution observations simultaneously in 10 discrete frequency bands sampling a wide spectral span (100-1500 MHz) in a nearly log-periodic fashion. The development of this system was primarily motivated by need for tomographic studies of pulsar polar emission regions. Although the system design is optimized for the primary goal, it is also suited for several other interesting astronomical investigations. The system consists of a dual-polarization multi-band feed (with discrete responses corresponding to the 10 bands pre-selected as relatively RFI-free), a common wide-band RF front-end, and independent back-end receiver chains for the 10 individual sub-bands. The raw voltage time-sequences corresponding to 16 MHz bandwidth each for the two linear polarization channels
2017 United States National Committee of URSI National Radio Science Meeting (USNC-URSI NRSM)
This paper provides a brief overview of the current Green Bank Telescope science program, and an ... more This paper provides a brief overview of the current Green Bank Telescope science program, and an update on technical developments performed since 2010.
We use time-domain electromagnetic simulations to assess the spectral characteristics of the dish... more We use time-domain electromagnetic simulations to assess the spectral characteristics of the dish antenna for the Hydrogen Epoch of Reionization Array (HERA). These simulations are part of a multi-faceted campaign to determine the effectiveness of the dish's design for obtaining a detection of redshifted 21 cm emission from the epoch of reionization. Our simulations show the existence of reflections between HERA's suspended feed and its parabolic dish reflector, at certain frequencies, with an amplitude of roughly $ -35$dB at 100 ns which can lead to some loss of measurable modes and a modest reduction in sensitivity. Even in the presence of this structure, we find that the spectral response of the dish is sufficiently smooth for delay filtering, a proven foreground isolation technique, to contain foreground emission at line-of-sight wave numbers below $k_\parallel \lesssim 0.2h$Mpc$^{-1}$, in the region where the current PAPER experiment operates. Incorporating these result...
To carry out astronomical observations in the molecule rich 3 mm window the Green Bank Telescope ... more To carry out astronomical observations in the molecule rich 3 mm window the Green Bank Telescope (GBT) compensates for gravitational and weather induced deformations of its primary reflector. Terrestrial laser scanners (TLSs) offer a fast and reliable means of measuring these deformations, but their use has been limited to measuring gravitational deformations thus far due to the large systematics inherent to their construction. The laser antenna surface scanning instrument (LASSI) on the GBT uses a TLS to measure weather induced deformations. The LASSI removes the TLS systematics by taking the difference between scans. We use the active surface (AS) on the GBT to validate this strategy and find that the LASSI can accurately measure deformations corresponding to different Zernike polynomials with amplitudes between 60 μm and 550 μm. We estimate that the wavefront error introduced by the LASSI to the surface is 100 ± 30 μm, root-mean-squared (rms), which would result in a total surfac...
The azimuth track of the Green Bank Telescope did not perform as designed. Relative movement of c... more The azimuth track of the Green Bank Telescope did not perform as designed. Relative movement of components was noted during construction; in addition, fretting of the base plate and wear plate faying surfaces, fatigue cracking of the wear plates, fatigue failure of wear plate fasteners, and deterioration of the cementitous grout layer occurred at a rapid pace during the first few years of operation. After extensive failure analysis, a new system of components was designed and fabricated, and installation of the components was performed during 2007 (Symmes, Anderson, and Egan, "Improving the service life of the 100m Green Bank Telescope azimuth track", SPIE 7012-121). The highlights and lessons learned during the fabrication and installation phases are described herein. This information will benefit any organization performing a similar replacement, and may be helpful in new installations as well.
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Papers by Dennis Egan