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NASA NTRS2021

Improvements to the Search for Cosmic Dawn Using the Long Wavelength Array

We present recent improvements to the search for the global Cosmic Dawn signature using the Long Wavelength Array station located on the Sevilleta National Wildlife Refuge in New Mexico, USA (LWA{SV). These improvements are both in the methodology of the experiment and the hardware of the station. An improved observing strategy along with more sophisticated temperature calibration and foreground modelling schemes have led to improved residual RMS limits. A large improvement over previous work using LWA{SV is the use of a novel achromatic beamforming technique which has been developed for LWA{SV. We present results from an observing campaign which contains 29 days of observations between March 10th, 2021 and April 10th 2021. The reported residual RMS limits are 6 times above the amplitude of the potential signal reported by the Experiment to Detect the Global EoR Signature (EDGES) collaboration.

Christopher Dilullo↗

NASA NTRSDate not supplied

Space-based Sensor for Extreme Fire Weather Events

Catastrophic bushfires are becoming increasingly prevalent as climate change advances. Impacts extend beyond national borders. Multinational efforts can inform new science and management practices. Space-based sensors and integrated data facilities will play an important role. This paper describes a collaborative project between a consortium of Australian universities and NASA Centers to develop and implement a small satellite platform comprising highly integrated thermal and lightning sensors coupled with AI-based edge computing to help predict, detect, and track bushfires, supporting mitigation activities. This will fill an important capability gap since Australia does not currently have any sovereign Earth observation satellites. This program is enabled by and builds on Australia-NASA collaboration and will also support fire science and management activities in the broader global context.

wildfire↗

NASA NTRS1998

The Double Edge Technique for Doppler lidar wind measurement

The edge technique utilizes the edge of a high spectral resolution filter for high accuracy wind measurement using direct detection lidar. The signal is split between an edge filter channel and a broadband energy monitor channel. The energy monitor channel is used for signal normalization. The edge measurement is made as a differential frequency measurement between the outgoing laser signal and the atmospheric backscattered return for each pulse. As a result, the measurement is insensitive to laser and edge filter frequency jitter and drift at a level less than a few parts in 10(exp 10). We will discuss the methodology of the technique in detail, present a broad range of simulation results, and provide preprints of a journal article currently in press.

Korb, C. Laurence↗

NASA NTRS1978

Flight experience on the need and use of inflight leading edge washing for a laminar flow airfoil

An investigation of leading-edge contamination by insects was conducted at the NASA Dryden Flight Research Center with a JetStar airplane instrumented to detect transition on the outboard leading-edge flap and equipped with a system to wash the leading edge in flight. The results of airline-type flights with the JetStar indicated that insects can contaminate the leading edge during take-off and climbout at large jet airports in the United States. The results also showed that the insects collected on the leading edges at 180 knots did not erode at cruise conditions for a laminar flow control airplane and caused premature transition of the laminar boundary layer. None of the superslick and hydrophobic surfaces tested showed any significant advantages in alleviating the insect contamination problem. While there may be other solutions to the insect contamination problem, the results of these tests with a washer system showed that a continuous water spray while encountering the insects is effective in preventing insect contamination of the leading edges.

Fisher, D. F.↗

NASA NTRS2020

TOI-824 b: A New Planet on the Lower Edge of the Hot Neptune Desert

We report the detection of a transiting hot Neptune exoplanet orbiting TOI-824 (SCR J1448-5735), a nearby (d = 64 pc) K4V star, using data from the Transiting Exoplanet Survey Satellite. The newly discovered planet has a radius Rp = 2.93 ± 0.20 Rꚛ and an orbital period of 1.393 days. Radial velocity measurements using the Planet Finder Spectrograph and the High Accuracy Radial velocity Planet Searcher spectrograph confirm the existence of the planet, and we estimate its mass to be 18.47 ± 1.84 Mꚛ. The planet's mean density is ρ(p)= 4.03 (+0.98,-0.78)g/cu. cm, making it more than twice as dense as Neptune. TOI-824 b's high equilibrium temperature makes the planet likely to have a cloud-free atmosphere, and thus it is an excellent candidate for follow-up atmospheric studies. The detectability of TOI-824 b's atmosphere from both ground and space is promising and could lead to the detailed characterization of the most irradiated small planet at the edge of the hot Neptune desert that has retained its atmosphere to date.

Jennifer A. Burt↗

NASA NTRS2018

Bow Shock in Merging Cluster A520: The Edge of the Radio Halo and the Electron-Proton Equilibration Timescale

We studied the prominent bow shock in the merging galaxy cluster A520 using a deep Chandra X-ray observation and archival VLA radio data. This shock is a useful diagnostic tool, owing to its clear geometry and relatively high Mach number. At the "nose" of the shock, we measure a Mach number of M=2.4(sup 0.4, sub -0.2). The shock becomes oblique away from the merger axis, with the Mach number falling to approx. 1.6 around 30 deg from the nose. The electron temperature immediately behind the shock nose is consistent with that from the Rankine-Hugoniot adiabat, and is higher (at a 95% confidence) than expected for adiabatic compression of electrons followed by Coulomb electron-proton equilibration, indicating the presence of equilibration mechanisms faster than Coulomb collisions. This is similar to an earlier finding for the Bullet cluster. We also combined four archival VLA data sets to obtain a better image of the cluster's giant radio halo at 1.4 GHz. An abrupt edge of the radio halo traces the shock front, and no emission is detected in the pre-shock region. If the radio edge were due only to adiabatic compression of relativistic electrons in pre-shock plasma, we would expect a pre-shock radio emission detectable in this radio data set; however, an interferometric artifact dominates the uncertainty, so we cannot rule this model out. Other interesting features of the radio halo include a peak at the remnant of the cool core, suggesting that the core used to have a radio minihalo, and a peak marking a possible region of high turbulence.

Wang, Qian H. S.↗

NASA NTRS2009

FPGA-Based Networked Phasemeter for a Heterodyne Interferometer

A document discusses a component of a laser metrology system designed to measure displacements along the line of sight with precision on the order of a tenth the diameter of an atom. This component, the phasemeter, measures the relative phase of two electrical signals and transfers that information to a computer. Because the metrology system measures the differences between two optical paths, the phasemeter has two inputs, called measure and reference. The reference signal is nominally a perfect square wave with a 50- percent duty cycle (though only rising edges are used). As the metrology system detects motion, the difference between the reference and measure signal phases is proportional to the displacement of the motion. The phasemeter, therefore, counts the elapsed time between rising edges in the two signals, and converts the time into an estimate of phase delay. The hardware consists of a circuit board that plugs into a COTS (commercial, off-the- shelf) Spartan-III FPGA (field-programmable gate array) evaluation board. It has two BNC inputs, (reference and measure), a CMOS logic chip to buffer the inputs, and an Ethernet jack for transmitting reduced-data to a PC. Two extra BNC connectors can be attached for future expandability, such as external synchronization. Each phasemeter handles one metrology channel. A bank of six phasemeters (and two zero-crossing detector cards) with an Ethernet switch can monitor the rigid body motion of an object. This device is smaller and cheaper than existing zero-crossing phasemeters. Also, because it uses Ethernet for communication with a computer, instead of a VME bridge, it is much easier to use. The phasemeter is a key part of the Precision Deployable Apertures and Structures strategic R&D effort to design large, deployable, segmented space telescopes.

Rao, Shanti↗

NASA NTRS2007

The Suzaku Observation of the Nucleus of the Radio Loud Active Galaxy Centaurus A: Constraints on Abundances in the Accreting Material

A Suzaku observation of the nucleus of the radio-loud AGN Centaurus A in 2005 has yielded a broadband spectrum spanning 0.3 to 250 keV. The hard X-rays are fit by two power laws, absorbed by columns of 1.5 and 7 x 10(exp 23) per square centimeter. The dual power-laws are consistent with previous suggestions that the powerlaw components are X-ray emission from the sub-pc VLBI jet and from Bondi accretion at the core, or are consistent with a partial covering interpretation. The soft band is dominated by thermal emission from the diffuse plasma and is fit well by a two-temperature VAPEC model, plus a third power-law component to account for scattered nuclear emission, kpc-scale jet emission, and emission from X-ray Binaries and other point sources. Narrow fluorescent emission lines from Fe, Si, S, Ar, Ca and Ni are detected. The width of the Fe Ka line yields a 200 light-day lower limit on the distance from the black hole to the line-emitting gas. K-shell absorption edges due to Fe, Ca, and S are detected. Elemental abundances are constrained via the fluorescent lines strengths, absorption edge depths and the diffuse plasma emission lines. The high metallicity ([Fe/H]=+0.l) of the circumnuclear material compared to that in the metal-poor outer halo suggests that the accreting material could not have originated in the outer halo unless enrichment by local star formation has occurred. Relative abundances are consistent with enrichment from Type II and Ia supernovae.

Markowitz, A.↗

NASA NTRS1988

Assessment of AVIRIS data from vegetated sites in the Owens Valley, California

Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data were acquired from the Bishop, CA area, located at the northern end of the Owens Valley, on July 30, 1987. Radiometrically-corrected AVIRIS data were flat-field corrected, and spectral curves produced and analyzed for pixels taken from both native and cultivated vegetation sites, using the JPS SPAM software program and PC-based spreadsheet programs. Analyses focussed on the chlorophyll well and red edge portions of the spectral curves. Results include the following: AVIRIS spectral data are acquired at sufficient spectral resolution to allow detection of blue shifts of both the chlorophyll well and red edge in moisture-stressed vegetation when compared with non-stressed vegetation; a normalization of selected parameters (chlorophyll well and near infrared shoulder) may be used to emphasize the shift in red edge position; and the presence of the red edge in AVIRIS spectral curves may be useful in detecting small amounts (20 to 30 pct cover) of semi-arid and arid vegetation ground cover. A discussion of possible causes of AVIRIS red edge shifts in respsonse to stress is presented.

Rock, B. N.↗

NASA NTRS1992

Observational evidence for thin AGN disks

AGN spectrum and spectral features, polarization, inclination, and X-ray line and continuum reflection features are discussed in a critical way in order to determine the ones that are the least model-dependent. The sign and strength of absorption and emission edges are found to be model-dependent, and relativistic broadening and shifting makes them hard to detect. The presence or absence of the predicted Lyman edge polarization feature may be used as a decisive test for thin, bare AGN disks. Other good model-independent tests are several inclination-related line and continuum correlations in big AGN samples. It is shown that electron temperature near the surface of the disk can greatly exceed the disk equilibrium temperature, which causes deviations from LTE. This effect must be incorporated into realistic disk models.

Netzer, Hagai↗

NASA NTRS2012

Subaru Imaging of Asymmetric Features in a Transitional Disk in a Transitional Disk in Upper Scorpius

We report high-resolution (0.07 arcsec) near-infrared polarized intensity images of the circumstellar disk around the star 2MASS J16042165−2130284 obtained with HiCIAO mounted on the Subaru 8.2 m telescope. We present our H-band data, which clearly exhibit a resolved, face-on disk with a large inner hole for the first time at infrared wavelengths.We detect the centrosymmetric polarization pattern in the circumstellar material as has been observed in other disks. Elliptical fitting gives the semimajor axis, semiminor axis, and position angle (P.A.) of the disk as 63 AU, 62 AU, and −14◦, respectively. The disk is asymmetric, with one dip located at P.A.s of ∼85◦. Our observed disk size agrees well with a previous study of dust and CO emission at submillimeter wavelength with Submillimeter Array. Hence, the near-infrared light is interpreted as scattered light reflected from the inner edge of the disk. Our observations also detect an elongated arc (50 AU) extending over the disk inner hole. It emanates at the inner edge of the western side of the disk, extending inward first, then curving to the northeast. We discuss the possibility that the inner hole, the dip, and the arc that we have observed may be related to the existence of unseen bodies within the disk

protoplanetary disks↗

NASA NTRS2012

Subaru Imaging of Asymmetric Features in a Transitional Disk in Upper Scorpius

We report high-resolution (0.07 arcsec) near-infrared polarized intensity images of the circumstellar disk around the star 2MASS J16042165.2130284 obtained with HiCIAO mounted on the Subaru 8.2 m telescope. We present our H-band data, which clearly exhibit a resolved, face-on disk with a large inner hole for the first time at infrared wavelengths. We detect the centrosymmetric polarization pattern in the circumstellar material as has been observed in other disks. Elliptical fitting gives the semi-major axis, semi-minor axis, and position angle (P.A.) of the disk as 63 AU, 62 AU, and -14deg, respectively. The disk is asymmetric, with one dip located at P.A.s of approx. 85deg. Our observed disk size agrees well with a previous study of dust and CO emission at submillimeter wavelength with Submillimeter Array. Hence, the near-infrared light is interpreted as scattered light reflected from the inner edge of the disk. Our observations also detect an elongated arc (50 AU) extending over the disk inner hole. It emanates at the inner edge of the western side of the disk, extending inward first, then curving to the northeast. We discuss the possibility that the inner hole, the dip, and the arc that we have observed may be related to the existence of unseen bodies within the disk.

Mayama, S.↗

NASA NTRS1983

The dynamics of elliptical rings

The paper investigates the evolution of eccentric rings under the influence of (1) differential precession due to the planetary quadrupole moment; (2) self-gravity; (3) viscous forces due to interparticle collisions; and (4) eccentricity excitation by shepherd satellites. The principal conclusions are that: (1) uniform precession can be enforced by self-gravity; the resulting configuration is both dynamically and secularly stable. (2) due to viscous forces the line of apsides at the inner ring edge is not exactly aligned with the line of apsides at the outer edge; the apse shift may be detectable in the alpha and beta rings of Uranus; (3) the mean eccentricity is determined by a balance between viscous damping and excitation by shepherds; (4) and the dimensionless eccentricity gradient is expected to be positive and of order unity in most eccentric rings, as observed.

Borderies, N.↗

NASA NTRS1987

On autonomous terrain model acquistion by a mobile robot

The following problem is considered: A point robot is placed in a terrain populated by an unknown number of polyhedral obstacles of varied sizes and locations in two/three dimensions. The robot is equipped with a sensor capable of detecting all the obstacle vertices and edges that are visible from the present location of the robot. The robot is required to autonomously navigate and build the complete terrain model using the sensor information. It is established that the necessary number of scanning operations needed for complete terrain model acquisition by any algorithm that is based on scan from vertices strategy is given by the summation of i = 1 (sup n) N(O sub i)-n and summation of i = 1 (sup n) N(O sub i)-2n in two- and three-dimensional terrains respectively, where O = (O sub 1, O sub 2,....O sub n) set of the obstacles in the terrain, and N(O sub i) is the number of vertices of the obstacle O sub i.

Rao, N. S. V.↗

NASA NTRS1990

IUE observations of PG 1115 + 080 - The He I Gunn-Peterson test and a search for the lensing galaxy

Five observations of PG 1115 + 080 taken with the IUE SWP camera have been combined in order to carry out the He I Gunn-Peterson test and to search for a Lyman limit which could determine the redshift of the lens candidate reported by Christian et al. (1987). No Lyman-limit discontinuities are found, implying that the lensing galaxy does not intercept the line of sight or does not contain enough neutral hydrogen to be detected as a Lyman-limit edge. It is estimated that the lens column density for neutral hydrogen is 3 x 10 to the 16th/sq cm or less if it intercepts the line of sight.

Tripp, Todd M.↗

NASA NTRS1994

Development of an accurate transmission line fault locator using the global positioning system satellites

A highly accurate transmission line fault locator based on the traveling-wave principle was developed and successfully operated within B.C. Hydro. A transmission line fault produces a fast-risetime traveling wave at the fault point which propagates along the transmission line. This fault locator system consists of traveling wave detectors located at key substations which detect and time tag the leading edge of the fault-generated traveling wave as if passes through. A master station gathers the time-tagged information from the remote detectors and determines the location of the fault. Precise time is a key element to the success of this system. This fault locator system derives its timing from the Global Positioning System (GPS) satellites. System tests confirmed the accuracy of locating faults to within the design objective of +/-300 meters.

Lee, Harry↗

NASA NTRS2012

Fabrication and Performance of Large Format Transition Edge Sensor Microcalorimeter Arrays

We have produced a variety of superconducting transition edge sensor array designs for microcalorimetric detection of x-rays. Designs include kilopixel scale arrays of relatively small sensors (~75 micron pitch) atop a thick metal heatsinking layer as well as arrays of membrane-isolated devices on 250 micron pitch and smaller arrays of devices up to 600 micron pitch. We discuss the fabrication techniques used for each type of array focusing on unique aspects where processes vary to achieve the particular designs and required device parameters. For example, we evaluate various material combinations in the production of the thick metal heatsinking, including superconducting and normal metal adhesion layers. We also evaluate the impact of added heatsinking on the membrane isolated devices as it relates to basic device parameters. Arrays can be characterized with a time division SQUID multiplexer such that greater than 10 devices from an array can be measured in the same cooldown. Device parameters can be measured simultaneously so that environmental events such as thermal drifts or changes in magnetic fields can be controlled. For some designs, we will evaluate the uniformity of parameters impacting the intrinsic performance of the microcalorimeters under bias in these arrays and assess the level of thermal crosstalk.

Chervenak, James A.↗

NASA NTRS2012

Large Format Transition Edge Sensor Microcalorimeter Arrays

Chervenak, J. A.↗