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NASA NTRS1981

Infrared Astronomy

Several observational programs in infrared astronomy are described and significant findings are briefly discussed. The near infrared work concentrates largely on the use of the 5 m Hale telescope in spectroscopic and photometric studies of extragalactic sources. Observations of the P alpha line profile in a low redshift quasar, X-ray bursters, reflection nebula, and cataclysmic variables are included. Millimeter continuum observations of dust emission from quasars and galactic molecular clouds are also discussed. Finally, improvements to instrumentation are reported.

Neugebauer, G.↗

DOE OSTI2022

Review of Radio Frequency Interference and Potential Impacts on the CMB-S4 Cosmic Microwave Background Survey

CMB-S4 will map the cosmic microwave background to unprecedented precision, while simultaneously surveying the millimeter-wave time-domain sky, in order to advance our understanding of cosmology and the universe. CMB-S4 will observe from two sites, the South Pole and the Atacama Desert of Chile. A combination of small- and large-aperture telescopes with hundreds of thousands of polarization-sensitive detectors will observe in several frequency bands from 20-300 GHz, surveying more than 50% of the sky to arcminute resolution with unprecedented sensitivity. CMB-54 seeks to make a dramatic leap in sensitivity while observing across a broad range of largely unprotected spectrum which is increasingly being utilized for terrestrial and satellite transmissions. Fundamental aspects of CMB instrument technology leave them vulnerable to radio frequency interference (RFI) across a wide range of frequencies, including frequencies outside of their observing bands. Ground-based CMB instruments achieve their extraordinary sensitivities by deploying large focal planes of superconducting bolometers to extremely dry, high-altitude sites, with large fractional bandwidths, wide fields of view, and years of integration time. Suitable observing sites have historically offered significant protection from RFI, both naturally through their extremely remote locations as well as through restrictions on local emissions. Since the coupling mechanisms are complex, "safe" levels or frequencies of emission that would not interfere with CMB measurements cannot always be determined through straightforward calculations. We discuss models of interference for various types of RFI relevant to CMB-54, mitigation strategies, and the potential impacts on survey sensitivity.

Cosmic Microwave Background↗

NASA NTRS1989

Structures for remotely deployable precision antennas

Future space missions such as the Earth Science Geostationary Platform (ESGP) will require highly accurate antennas with apertures that cannot be launched fully formed. The operational orbits are often inaccessible to manned flight and will involve expendable launch vehicles such as the Delta or Titan. There is therefore a need for completely deployable antenna reflectors of large size capable of efficiently handling millimeter wave electromagnetic radiation. The parameters for the type of mission are illustrated. The logarithmic plot of frequency versus aperture diameter shows the regions of interest for a large variety of space antenna applications, ranging from a 1500-meter-diameter radio telescope for low frequencies to a 20-meter-diameter infrared telescope. For the ESGP, a major application is the microwave radiometry at high frequencies for atmospheric sounding. Almost all existing large antenna reflectors for space employ a mesh-type reflecting surface. Examples are shown and discussed which deal with the various structural concepts for mesh antennas. Fortunately, those concepts are appropriate for creating the very large apertures required at the lower frequencies for good resolution. The emphasis is on the structural concepts and technologies that are appropriate to fully automated deployment of dish-type antennas with solid reflector surfaces. First the structural requirements are discussed. Existing concepts for fully deployable antennas are then described and assessed relative to the requirements. Finally, several analyses are presented that evaluate the effects of beam steering and segmented reflector design on the accuracy of the antenna.

Hedgepeth, J. M.↗

NASA NTRS2015

Fabrication of Feedhorn-Coupled Transition Edge Sensor Arrays for Measurement of the Cosmic Microwave Background Polarization

Characterization of the minute cosmic microwave background (CMB) polarization signature requires multi-frequency high-throughput precision instrument systems. We have previously described the detector fabrication of a 40 gigahertz focal plane and now describe the fabrication of a 37-element dual-polarization detector module for measurement of the CMB at 90 gigahertz. The 72-TES (Transition Edge Sensor)-based bolometers in each module are coupled to a niobium-based planar orthomode transducer with integrated band defining filters implemented in microstrip transmission line. A single crystal silicon dielectric substrate serves as microstrip dielectric and as a thermal link between the membrane isolated MoAu TES operating at 150 millikelvins and the heat bath. A short silicon leg between the heat bath and the TES bolometer is designed for ballistic phonon transport and provides improved process control and uniformity of thermal conductance in the presence of phonon scattering on roughened surfaces. Micro-machined structures are used to realize the orthomode transducer backshort, provide out of band signal rejection, and a silicon photonic choke for feedhorn coupling are described. The backshort, choke wafer, and detector wafer are indium bump-bonded to create a single 37-element dual-polarization detector module. Fourteen such hexagonally shaped modules each 80 millimeters in size comprise two focal planes. These, along with the recently delivered 40 gigahertz focal plane, will survey a large fraction of the sky as part of the Johns Hopkins University-led ground-based CLASS (Cosmology Large Angular Scale Surveyor) telescope.

Detectors↗

DOE OSTI2024

Flaring Stars in a Non-targeted mm-wave Survey with SPT-3G

We present a flare star catalog from four years of non-targeted millimeter-wave survey data from the South Pole Telescope (SPT). The data were taken with the SPT-3G camera and cover a 1500-square-degree region of the sky from $20^{h}40^{m}0^{s}$ to $3^{h}20^{m}0^{s}$ in right ascension and $-42^{\circ}$ to $-70^{\circ}$ in declination. This region was observed on a nearly daily cadence from 2019-2022 and chosen to avoid the plane of the galaxy. A short-duration transient search of this survey yields 111 flaring events from 66 stars, increasing the number of both flaring events and detected flare stars by an order of magnitude from the previous SPT-3G data release. We provide cross-matching to Gaia DR3, as well as matches to X-ray point sources found in the second ROSAT all-sky survey. We have detected flaring stars across the main sequence, from early-type A stars to M dwarfs, as well as a large population of evolved stars. These stars are mostly nearby, spanning 10 to 1000 parsecs in distance. Most of the flare spectral indices are constant or gently rising as a function of frequency at 95/150/220 GHz. The timescale of these events can range from minutes to hours, and the peak $\nu L_{\nu}$ luminosities range from $10^{27}$ to $10^{31}$ erg s$^{-1}$ in the SPT-3G frequency bands.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2013

A Measurement of the Millimeter Emission and the Sunyaev-zel'dovich Effect Associated with Low-frequency Radio Sources

We present a statistical analysis of the millimeter-wavelength properties of 1.4 GHz-selected sources and a detection of the Sunyaev-Zel'dovich Effect associated with the halos that host them. The Atacama Cosmology Telescope (ACT) has conducted a survey at 148 GHz, 218 GHz and 277 GHz along the celestial equator. Using samples of radio sources selected at 1.4 GHz from the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) Survey and the National Radio Astronomy Observatory Very Large Array Sky Survey (NVSS), we measure the stacked 148, 218 and 277 GHz flux densities for sources with 1.4 GHz flux densities ranging from 5 to 200 mJy. At these flux densities, the radio source population is dominated by active galactic nuclei (AGN), with both steep and at spectrum populations, which have combined radio-to-millimeter spectral indices ranging from 0.5 to 0.95, reecting the prevalence of steep spectrum sources at high flux densities and the presence of at spectrum sources at lower flux densities. The thermal Sunyaev-Zelapos;dovich (SZ) eect associated with the halos that host the AGN is detected at the 5 level through its spectral signature. When we compare the SZ eect with weak lensing measurements of radio galaxies, we find that the relation between the two is consistent with that measured by Planck for local bright galaxies. We present a detection of the SZ eect in some of the lowest mass halos (average M(sub 200) approx. equals 10(exp 13) solar M h(sup-1) (sub 70) ) studied to date. This detection is particularly important in the context of galaxy evolution models, as it confirms that galaxies with radio AGN also typically support hot gaseous halos. With Herschel* observations, we show that the SZ detection is not significantly contaminated by dusty galaxies or by dust associated with the AGN or galaxies hosting the AGN. We show that 5 mJy < S(sub 1:4) < 200 mJy radio sources contribute l(l +1)C(sub l)/(2 pi ) = 0:37+/- 0:03 micro K(exp 2) to the angular power spectrum at l = 3000 at 148 GHz, after accounting for the SZ effect associated with their host halos.

galaxies↗

NASA NTRS2014

A Measurement of the Millimeter Emission and the Sunyaev-Zel'dovich Effect Associated with Low-Frequency Radio Sources

We present a statistical analysis of the millimeter-wavelength properties of 1.4 GHz-selected sources and a detection of the Sunyaev-Zel'dovich effect associated with the halos that host them. We stack data at 148, 218 and 277 GHz from the Atacama Cosmology Telescope at the positions of a large sample of radio AGN selected at 1.4 GHz. The thermal Sunyaev-Zel'dovich (SZ) effect associated with the halos that host the AGN is detected at the 5 sigma level through its spectral signature, representing a statistical detection of the SZ effect in some of the lowest mass halos (average M(sub 200) approximately equals 10(sup 13) solar mass h(sub 70)(exp −1) ) studied to date. The relation between the SZ effect and mass (based on weak lensing measurements of radio galaxies) is consistent with that measured by Planck for local bright galaxies. In the context of galaxy evolution models, this study confirms that galaxies with radio AGN also typically support hot gaseous halos. Adding Herschel observations allows us to show that the SZ signal is not significantly contaminated by dust emission. Finally, we analyze the contribution of radio sources to the angular power spectrum of the cosmic microwave background.

radio continuum↗

NASA NTRSDate not supplied

Tangerine Dream: Observations of Titan from the Earth

From its discovery in 1655 by the Dutch astronomer Christiaan Huygens, Titan perplexed and confounded Earth-based astronomers for three centuries with its stubborn refusal to yield virtually any clues about its nature. Until the Voyager 1 1980, even fundamentals such as its true diameter, surface pressure, and major atmospheric gas were uncertain [1]. Most of the information we now know about Titan has been wrestled at great expense of time and effort by three spacecraft visitors: Voyager 1, Cassini and Huygens. So why then continue to bother with Earth-based telescopic observations? In this review talk I will describe how significant clues about Titan’s atmospheric composition began to emerge from ground-based observations in the 1940s through 1970s, in the run-up to the revolutionary Voyager 1 flyby. These included the discovery of methane [2], and other significant hydrocarbons including ethane and acetylene in Titan’s stratosphere [3, 4]. Further ground and space-based telescopic work in the 1980s and 1990s revealed the presence of the fourth most abundance gas, carbon monoxide [5], spotted for the first time the bright continent on Titan’s leading hemisphere now known as Xanadu [6], and the comings and goings of bright tropospheric clouds [7]. The Cassini-Huygens mission of 2004-2017 [8, 9] greatly expanded our knowledge of Titan, including the first in situ measurements of the atmosphere and detailed imaging of the surface. However in the two-decades long gap before the next mission, Dragonfly, reaches Titan we are finding new ways to further our knowledge of Titan using the current generation of telescopes and instruments. With high-resolution spectroscopy at infrared and sub-millimeter wavelengths we are finding new chemical constituents in the atmosphere, and even measuring wind fields at middle altitudes. I will conclude by discussing how the next generation of Earth and space-based telescopes and instruments promises yet more breakthroughs via astronomy, including with large aperture 30 and 40 meter class telescopes that will become available in the late 2020s, and spectroscopy with airborne

Titan↗

DOE OSTI2024

Atacama Large Aperture Submillimeter Telescope (AtLAST) science: Resolving the hot and ionized Universe through the Sunyaev-Zeldovich effect

An omnipresent feature of the multi-phase “cosmic web” — the large-scale filamentary backbone of the Universe — is that warm/hot (≳ 10 5 K) ionized gas pervades it. This gas constitutes a relevant contribution to the overall universal matter budget across multiple scales, from the several tens of Mpc-scale intergalactic filaments, to the Mpc intracluster medium (ICM), all the way down to the circumgalactic medium (CGM) surrounding individual galaxies, on scales from ~ 1 kpc up to their respective virial radii (~ 100 kpc). The study of the hot baryonic component of cosmic matter density represents a powerful means for constraining the intertwined evolution of galactic populations and large-scale cosmological structures, for tracing the matter assembly in the Universe and its thermal history. To this end, the Sunyaev-Zeldovich (SZ) effect provides the ideal observational tool for measurements out to the beginnings of structure formation. The SZ effect is caused by the scattering of the photons from the cosmic microwave background off the hot electrons embedded within cosmic structures, and provides a redshift-independent perspective on the thermal and kinematic properties of the warm/hot gas. Still, current and next-generation (sub)millimeter facilities have been providing only a partial view of the SZ Universe due to any combination of: limited angular resolution, spectral coverage, field of view, spatial dynamic range, sensitivity, or all of the above. In this paper, we motivate the development of a wide-field, broad-band, multi-chroic continuum instrument for the Atacama Large Aperture Submillimeter Telescope (AtLAST) by identifying the scientific drivers that will deepen our understanding of the complex thermal evolution of cosmic structures. On a technical side, this will necessarily require efficient multi-wavelength mapping of the SZ signal with an unprecedented spatial dynamic range (from arcsecond to degree scales) and we employ detailed theoretical forecasts to determine the key instrumental constraints for achieving our goals.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1980

Space astronomy to the year 2000 - A preview of the possibilities

Following an overview of the role of space observations in contemporary astrophysics, the next generation of space-based observatories (the Space Telescope, the Gamma Ray Observatory and the Advanced X-Ray Astrophysics Facility) is described. Possible new directions which may be pursued in the 1990s are also discussed. These include the development of large flux collectors for use in astronomy in the ultraviolet, optical, infrared and millimeter wave portions of the spectrum and the development of space-based interferometers to carry out a variety of astrophysically important measurements. Many of these longer term programs will require substantial advances in optics, structures, and control technology.

Rosendhal, J. D.↗

NASA NTRS1993

The contribution of disks and envelopes to the millimeter continuum emission from very young low-mass stars

We investigate the question of disk formation during the protostar phase. We model the dust continuum emission from the dense cloud core using the cloud-collapse models of Terebey et al. (1984) and show that dust emission from the dense core is important when measured with large single-dish telescopes at 1.3 mm, but nearly negligible with interferometers at 2.7 mm. From published and new data, we conclude that massive disks are also seen toward a number of other sources including L1448 IRS 3, whose disk mass is estimated to be 0.5 solar mass. However, 1.3 mm data show that massive disks are relatively rare, occurring around perhaps 5 percent of young embedded stars. This implies that either massive disks occur briefly during the embedded phase or that relatively few young stars form massive disks. The median 1.3 mm flux density of IRAS-Dense cores in our sample is nearly the same as T Tauri stars in the sample of Beckwith et al. (1990). We conclude that the typical disk mass is not significantly higher during the embedded phase than during the later T Tauri phase.

Terebey, S.↗

DOE OSTI2022

New Identifications and Multiwavelength Properties of Extragalactic Fermi Gamma-Ray Sources in the SPT-SZ Survey Field

he fourth Fermi Large Area Telescope catalog (4FGL) contains 5064 $\ γ$-ray sources detected at high significance, but 26% of them still lack associations at other wavelengths. The SPT-SZ survey, conducted between 2008 and 2011 with the South Pole Telescope (SPT), covers 2500 deg 2 of the southern sky in three millimeter-wavelength (mm) bands and was used to construct a catalog of nearly 5000 emissive sources. In this study, we introduce a new cross-matching scheme to search for multiwavelength counterparts of extragalactic $\ γ$-ray sources using a mm catalog. We apply a Poissonian probability to evaluate the rate of spurious false associations and compare the multiwavelength associations from the radio, mm, near-infrared, and X-ray with 4FGL $\ γ$-ray sources. In the SPT-SZ survey field, 85% of 4FGL sources are associated with mm counterparts. These mm sources include 94% of previously associated 4FGL sources and 56% of previously unassociated 4FGL sources. The latter group contains 40 4FGL sources for which SPT has provided the first identified counterparts. Nearly all of the SPT-associated 4FGL sources can be described as flat-spectrum radio quasars or blazars. We find that the mm band is the most efficient wavelength for detecting $\ γ$-ray blazars when considering both completeness and purity. We also demonstrate that the mm band correlates better to the $\ γ$-ray band than the radio or X-ray bands. With the next generation of CMB experiments, this technique can be extended to greater sensitivities and more sky area to further complete the identifications of the remaining unknown $\ γ$-ray blazars.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1973

The Hat Creek millimeter-wave interferometer.

A fixed-baseline millimeter-wave interferometer, operating initially at 13.5 mm, has been put into operation at the Hat Creek Observatory as the first step in the development of a two-element aperture synthesis telescope. The first system consists of a 3-m antenna and a 6-m antenna spaced 265 m apart. Large receiver bandwidths may be used at high frequencies, and this system employs an intermediate frequency bandwidth of about 400 MHz. The instrument has been used to derive accurate absolute positions of interstellar water vapor sources, to study Mercury, Venus, and Mars, and to make crude maps of a few complex continuum sources. The synthesis telescope, the next stage, has two 6-m antennas which can be located at various stations on a T-shaped track. The east-west leg is 300 m and the north-south leg is 200 m, permitting full synthesis for sources on the equator and at declinations as low as -30 deg as well as at high declinations.

Hills, R. E.↗

NASA NTRS2005

A SAFIR Mission Concept

The development of a large far-infrared telescope in space has taken on a new urgency with the recognition of the fundamental importance of the far-infrared spectral region to questions ranging from cosmology to our own Solar System. The Single Aperture Far-InfraRed (SAFIR) Observatory is a l0m-class far-infrared observatory that would begin development later in this decade to answer these questions. SAFIR's science goals are driven by the fact that youngest stages of almost all phenomena in the universe are shrouded in absorption by and emission from cool dust that emits strongly in the far- infrared, 20 microns - 1 millimeter. Its operating temperature of 4 K and its capable instrument complement would be optimized to reach the natural sky background limit in the far-infrared with diffraction-limited performance down to around 40 microns. This would provide a point source sensitivity improvement of several orders of magnitude over that of SIRTF. Based on a broad set of science requirements, we have developed a conceptual design for the SAFIR observatory using design heritage from the James Webb Space Telescope. Several enabling technologies requiring development have been identified, including lightweight deployable optics, cryogenic cooling of optical elements and instruments, and large arrays of sensitive detectors.

Benford, Dominic J.↗

NASA NTRS2003

VLA Imaging of Protoplanetary Environments

Our program uses the techniques of millimeter interferometry to make high resolution observations of dust continuum emission to study the structure of protoplanetary disks around nearby stars. We continue to use the Very Large Array (VLA) of the National Radio Astronomy Observatories (NRAO) to make produce high angular resolution images, and we are improving our capabilities to interpret these observations with detailed numerical models. We have also made the first millimeter interferometer observations of protoplanetary disks in the southern hemisphere, using the recently upgraded Australia Telescope Compact Array (ATCA), taking advantage of the techniques we have developed in our work on northern sources.

Wilner, David J.↗

NASA NTRS1975

Astronomy at sub-millimeter wavelengths

The first flight test of a gondola containing a Newtonian telescope with a 16 in. primary mirror is described. Bolometer tests were conducted along with gondola design studies, and changes were made in the mechanical system as a result. Parts of the system were rebuilt and tested, and it was found that the flight system had redundant data recording capabilities. In the total flight record, about 160 large signals were noted; about half of these appeared to have the correct shape for genuine signals, and the other were clearly noise spikes (they were large but the signal shape could not have been produced by the observation of a celestial object).

Friedlander, M. W.↗

NASA NTRS2004

Design and Fabrication of a Two-Dimensional Superconducting Pop-up Bolometer Array

We have been developing an architecture for producing large format, two dimensional arrays of close-packed bolometers, which will enable submillimeter cameras and spectrometers to obtain images and spectra orders of magnitude faster than present instruments. The low backgrounds achieved in these instruments require very sensitive detectors with NEPs of order 5 x 10(exp -18) W/square root of Hz. Superconducting transition edge sensor bolometers can be close-packed using the Pop-up Detector (PUD) format, and SQUID multiplexers operating at the detector base temperature can be intimately coupled to them. The array unit cell is 8 x 32 pixels, using 32- element detector and multiplexer components. We have fabricated an engineering model array with this technology which features a very compact, modular approach for large format arrays. We report on the production of the 32-element components for the arrays. Planned instruments using this array architecture include the Submillimeter and Far-InfraRed Experiment (SAFIRE) on the SOFIA airborne observatory, the South Pole Imaging Fabry-Perot Interferometer (SPIFI) for the AST/RO observatory, the Millimeter Bolometer Camera for the Atacama Cosmology Telescope (MBC/ACT), and the Redshift (Z) Early Universe Spectrometer (ZEUS j.

Benford, Dominic J.↗

NASA NTRS1983

Millimeter-wave studies of the surfaces of Mercury and Mars and the atmosphere of Venus

Disk average brightness temperatures of Mercury were obtained using a 4.6 m radio telescopes. The data was searched for periodicities which correlate with phase angle, hermocentric longitude and beat frequencies produced by modulations of various celestial mechanical parameters. Spectral line observations were made of Venus with the NRAO 11 m radio telescope. The total CO content and the CO vertical profile, and their variability were observed. Large scale thermophysical properties of the surface of Mars were studied.

Epstein, E. E.↗