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NASA NTRS1972

Lunar composition from Apollo orbital measurements

Several spectrometers carried in the Service Module of the Apollo 15 and Apollo 16 spacecraft were employed for the compositional mapping of the lunar surface. The observations involved the measurements of secondary (fluorescent) X-rays, gamma rays and alpha particle emissions. A large scale compositional map of over 20 percent of the lunar surface was obtained for the first time. It was possible to demonstrate interesting chemical differences between the mare and the highlands, to find specific areas of high radioactivity and to learn something about the composition of the moon's hidden side. Further the same devices were used to obtain useful astronomical data during the return to earth.

Adler, I.↗

DOE OSTI2022

A Self-learning Neural Network Approach for Radio Frequency Interference Detection and Removal in Radio Astronomy

In this work, we present a novel neural network (NN) method for the detection and removal of radio frequency interference (RFI) from the raw digitized signal in the signal processing chain of a typical radio astronomy experiment. The main advantage of our method is that it does not require a training set. Instead, our method relies on the fact that the true signal of interest coming from astronomical sources is thermal and therefore described as a Gaussian random process, which cannot be compressed. We employ a variational encoder/decoder network to find the compressible information in the data stream that can explain the most variance with the fewest degrees of freedom. We demonstrate it on a set of toy problems and stored ring buffers from the Baryon Mapping eXperiment prototype. We find that the RFI subtraction is effective at cleaning simulated time streams: While we find that the power spectra of the RFI-cleaned time streams output by the NN suffer from extra signal consistent with additive noise, we find that it is generally around percent level across the band and sub 10% in contaminated spectral channels even when RFI power is an order of magnitude larger than the signal. We discuss the advantages and limitations of this method and possible implementation in the front end of future radio experiments.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1975

The new Martian nomenclature of the International Astronomical Union

A new nomenclature for Martian regions and topographic features uncovered by Mariner 9, as officially adopted by the International Astronomical Union, is described. About 180 craters generally of diameters greater than 100 km have been named, as well as 13 classes of topographic features designated catena, chasma, dorsum, fossa, labyrinthus, mensa, mons, patera, planitia, planum, tholus, vallis, and vastitas. In addition seven craters and the Kepler Dorsum are named on Phobos, and two craters on Deimos. Coordinates and maps of each named feature are displayed.

De Vaucouleurs, G.↗

NASA NTRS2000

A Model for Removing Fringes from STIS Slitless Spectra

We have developed a model that allows us to defringe slitless 2-dimensional spectra taken with the Space Telescope Imaging Spectrograph (STIS). Like all thin chip CCDs used in astronomy, the STIS CCD detector acts like an interferometer in the presence of monochromatic light, producing bright and dark fringes where there is constructive and destructive interference. These fringes are especially troublesome for spectra in the near-IR (> 7000A), reaching a peak amplitude of about 20% near 9500 A. Removing fringes from STIS spectra taken with a slit is simply a matter of dividing by an appropriate "fringe flat". A suitable flat is obtained by observing a continuum calibration source through the same slit. This however is not possible for slitless spectra, whose wavelength mapping onto the CCD detector varies with position of the object in the field. Beginning with an approximate knowledge of the STIS CCD structure, we have used 50 continuum source spectral flats taken at various central wavelengths to constrain the thickness of the detection layer at each pixel. Rom this result, we can compute a fringe flat for any astronomical source, no matter how it is positioned in the field. Flats made by this method reduce the fringing amplitude in astronomical spectra by a factor of about 5. The model fringe flat is a function of the index of refraction of each of four layers in the CCD, the thickness of each layer, and the wavelength of the light hitting each pixel. We show how the CCD structural parameters are incorporated into this "fitting function", and describe the procedure used to solve for the free parameters (the thickness of each layer at each pixel). The effectiveness of this technique will be demonstrated using slitless spectra taken as part of the STIS parallel program.

Malumuth, E.M.↗

NASA NTRS1986

Occultation studies with small telescopes

The data which can be acquired by observing occultations of stars by asteroids, the Pluto-Charon system, and comets using small telescopes are reviewed. A network of small telescopes may be the only possible means of observing a few specific types of occultations. The occultations are usually sufficiently bright so that small aperture telescopes can easily obtain high signal/noise ratios. The techniques and equipment are accessible to both professional, amateur and student astronomers, which is a favorable situation since only a small percentage of the nearly-hourly occurrence of occultations of stars by minor and distant planetary bodies are ever observed. Techniques employed for measuring the dimensions of asteroids by combining chords measured by distributed small telescopes are described and examples are provided of asteroids for which complete or incomplete size/density mappings have been made.

Millis, Robert L.↗

NASA NTRSDate not supplied

On the Alleviation of the Impact of Spaceborne RFI on Geodetic VLBI Results

Radio astronomy observations are under a growing threat from the rapidly growing number of communication satellites. Especially those in low earth orbit. These satellite not only emit at frequencies crucial to radio astronomny, including VLBI, but they also do it at a much stronger signal than the astronomical sources (quasars and pulsars) we are interested in. We therefore present a dynamic mask that will scan the sky and avoid pointing in directions that may be under threat of radio frequency interruption (RFI) from these satellites at a given time. We also present our database of all the potentially threatening satellites, that is updated daily and used to map out the satellites in the sky. Finally, we present results from actual tracking of a radio emitting satellites, and show how these affected our VLBI analysis.

VLBI↗

NASA NTRS1994

Infrared astronomy from the Moon

The purpose of this paper is to exhibit the advantages and limitations to infrared astronomical observations form the moon. The most obvious apparent advantage is the lack of a lunar atmosphere; radiation arriving from the universe is neither extinguished nor refracted as it approaches the lunar surface. However, the Earth's atmosphere's protection against cosmic rays is also lost, and infrared detectors are highly sensitive to irradiation by energetic particles. A second apparent advantage is the relative ease with which beams from an array of telescopes can be interferometrically combined; again the vacuum environment with constant refractive index of unity throughout, permits combination without phase delay across the entire spectral range. But thermal radiation from optical components and stray radiation from the lunar environment, just outside the light path, tend to lessen that advantage, except in narrow-spectral-band spatial interferometry, in which only the radiation in individual spectral lines is mapped, and broad-band thermal emission can be effectively filtered out. On the Moon's night side, and in polar craters on the Moon, radiative cooling should permit the attainment of high sensitivity with large telescopes. Just as the proposed Edison spacecraft primary mirror is expected to reach temperatures around 40 K, so also large lunar primary mirrors might be expected to reach temperatures in that range, making the zodiacal glow the main source of noise at wavelengths shortward of 25 micrometers. The slow rota tion of the Moon, and the lack of vibrations from natural sources such as winds, should provide advantages in guiding on specific astronomical sources. To learn as much as possible about the difficulties of remote observations in a hostile environment, Antarctic observatories should be used as test beds for the rigors of lunar observations. The strenuous requirements for successful astronomical observations from the South Pole are similar to those expected to be encountered in observations conducted from the Moon.

Harwit, Martin↗

NASA NTRS2007

Coordinated Chemical and Isotropic Studies of IDPS: Comparison of Circumstellar and Solar GEMS Grains

Silicate stardust in IDPs and meteorites include forsterite, amorphous silicates, and GEMS grains [1]. Amorphous presolar silicates are much less abundant than expected based on astronomical models [2], possibly destroyed by parent body alteration. A more accurate accounting of presolar silicate mineralogy may be preserved in anhydrous IDPs. Here we present results of coordinated TEM and isotopic analyses of an anhydrous IDP (L2005AL5) that is comprised of crystalline silicates and sulfides, GEMS grains, and equilibrated aggregates embedded in a carbonaceous matrix. Nanometer-scale quantitative compositional maps of all grains in two microtome thin sections were obtained with a JEOL 2500SE. These sections were then subjected to O and N isotopic imaging with the JSC NanoSIMS 50L. Coordinated high resolution chemical maps and O isotopic com-positions were obtained on 11 GEMS grains, 8 crystalline grains, and 6 equilibrated aggregates.

Keller, L. P.↗

DOE OSTI2025

User Guide for BLADE_LC_processor.py

BLADE_LC_processor.py is an optional script within the BLADE (Bolide Light-curve Analysis and Discrimination Explorer) open-source software package. It converts per-event light curve CSVs plus a metadata table into maps, plots, a per-sample trajectory file, and an aggregate summary. It anchors each trajectory at peak brightness, assumes constant speed and entry angle across the event, and propagates altitude and ground track relative to that anchor. The script converts the input azimuth internally to a travel bearing for the map and trajectory. Outputs include event folders with figures and a consolidated CSV containing start, peak, and end altitudes and all original metadata, sorted newest to oldest. For further background, users are referred to the foundational publication: Silber, E. A., Sawal, V. (2025), “BLADE: An Automated Framework for Classifying Light Curves from the Center for Near-Earth Object Studies Fireball Database,” The Astronomical Journal, doi: 10.3847/1538-3881/adeb55.

97 MATHEMATICS AND COMPUTING↗

NASA NTRS2013

Properties of Polycyclic Aromatic Hydrocarbons in the Northwest Photon Dominated Region of NGC 7023. I. PAH Size, Charge, Composition, and Structure Distribution

Polycyclic aromatic hydrocarbon (PAH) emission in the Spitzer Infrared Spectrograph spectral map of the northwest photon dominated region (PDR) in NGC 7023 was analyzed exclusively using PAH spectra from the NASA Ames PAH IR Spectroscopic Database (www.astrochem.org/pahdb). The 5-15 micron spectrum at each pixel is fitted using a non-negative-least-squares fitting approach. The fits are of good quality, allowing decomposition of the PAH emission into four subclasses: size, charge, composition, and hydrogen adjacency (structure). Maps tracing PAH subclass distributions across the region paint a coherent astrophysical picture. Once past some 20 seconds of arc from HD 200775, the emission is dominated by the more stable, large, symmetric, compact PAH cations with smaller, neutral PAHs taking over along the lines-of-sight toward the more distant molecular cloud. The boundary between the PDR and the denser cloud material shows up as a distinct discontinuity in the breakdown maps. Noteworthy is the requirement for PANH cations to fit the bulk of the 6.2 and 11.0 micron features and the indication of PAH photo-dehydrogenation and fragmentation close to HD 200775. Decomposition of the spectral maps into "principal" subclass template spectra provides additional insight into the behavior of each subclass. However, the general applicability of this computationally more efficient approach is presently undetermined. This is the first time the spectra of individual PAHs are exclusively used to fit the 5-15 micron region and analyze the spatial behavior of the aromatic infrared bands, providing fundamental, new information about astronomical PAH subpopulations including their dependence on, and response to, changes in local conditions.

northwest photon↗

NASA NTRS1990

BATSE software for the analysis of the gamma ray burst spatial distribution

The Burst and Transient Source Experiment (BATSE) on the Gamma Ray Observatory (GRO) is designed to study astronomical gamma ray sources and to provide better positional, spectral, and time resolution about these objects than has previously been possible from one experiment. The procedure to be used in the analysis of the gamma ray burst spatial distribution is presented. Data is input from BATSE via the Gamma Ray Burst Catalog (listing individual burst positions, flux values, and associated errors) and the Sky Sensitivity Map (which summarizes observational selection effects in table format). A FORTRAN program generates Monte Carlo burst catalogs, which are models to be compared to the actual distribution. The Monte Carlo models are then filtered through the Sky Sensitivity Map so that they suffer from the same selection effects as the actual catalog data. Additionally, each burst position is converted into a probability distribution to mimic BATSE positional sensitivity. The Burst Catalog, Monte Carlo burst catalog, and Sky Sensitivity Map are then passed onto an IDL program that compares the catalogs for statistical significance. The Sky Sensitivity Map is used to estimate how often each sky area is observed above the minimum flux level in question. Each burst found in this sky area is then weighted according to the frequency with which this sky area is observed. The catalogs are then compared via tests of homogeneity (based on their radial distributions) and isotropy (based upon their angular distributions). The results of the statistical comparisons along with graphs and charts of the summaries, are output from the IDL program for study.

Hakkila, Jon↗

NASA NTRS1978

IAU nomenclature for albedo features on the planet Mercury

The International Astronomical Union has endorsed a nomenclature for the albedo features on Mercury. Designations are based upon the mythological names related to the god Hermes; they are expressed in Latin form. The dark-hued albedo features are associated with the generic term Solitudo. The light-hued areas are designated by a single name without generic term. The 32 names adopted are allocated on the Mercury map.

Dollfus, A.↗

NASA NTRS2010

The Mineralogy of Circumstellar Silicates Preserved in Cometary Dust

Interplanetary dust particles (IDPs) contain a record of the building blocks of the solar system including presolar grains, molecular cloud material, and materials formed in the early solar nebula. Cometary IDPs have remained relatively unaltered since their accretion because of the lack of parent body thermal and aqueous alteration. We are using coordinated transmission electron microscope (TEM) and ion microprobe studies to establish the origins of the various components within cometary IDPs. Of particular interest is the nature and abundance of presolar silicates in these particles because astronomical observations suggest that crystalline and amorphous silicates are the dominant grain types produced in young main sequence stars and evolved O-rich stars. Five circumstellar grains have been identified including three amorphous silicate grains and two polycrystalline aggregates. All of these grains are between 0.2 and 0.5 micrometers in size. The isotopic compositions of all five presolar silicate grains fall within the range of presolar oxides and silicates, having large (17)O-enrichments and normal (18)O/(16)O ratios (Group 1 grains from AGB and RG stars). The amorphous silicates are chemically heterogeneous and contain nanophase FeNi metal and FeS grains in a Mg-silicate matrix. Two of the amorphous silicate grains are aggregates with subgrains showing variable Mg/Si ratios in chemical maps. The polycrystalline grains show annealed textures (equilibrium grains boundaries, uniform Mg/Fe ratios), and consist of 50-100 nm enstatite and pyrrhotite grains with lesser forsterite. One of the polycrystalline aggregates contains a subgrain of diopside. The polycrystalline aggregates form by subsolidus annealing of amorphous precursors. The bulk compositions of the five grains span a wide range in Mg/Si ratios from 0.4 to 1.2 (avg. 0.86). The average Fe/Si (0.40) and S/Si (0.21) ratios show a much narrower range of values and are approximately 50% of their solar abundances. The latter observation may indicate a decoupling of the silicate and sulfide components in grains that condense in stellar outflows. The amorphous silicate grains described here were not extensively affected by irradiation, sputtering, or thermal processing and may represent relatively pristine circumstellar grains. They are strong candidates for the "dirty silicates" in astronomical observations of circumstellar dust shells. The polycrystalline grains were originally amorphous silicate grains that were likely annealed in the early solar nebula but the processing was not sufficient to erase their anomalous oxygen isotopic compositions.

Keller, L. P.↗

NASA NTRS2009

High Spectral Resolution Infrared Studies of Titan: Winds, Temperature and Composition

Results from the most recent analyses of resolved ethane Line emission profiles from the stratosphere of Titan, measured before (2003) [1, 2], near the time of (2005) [3, 4], and after (2008) Huygens descent, will be presented. Wind velocity, temperature and ethane abundance are retrieved from 11.7 micron measurements at spectral resolving, powers > 1000000 using the NASA Goddard Space Flight Center Heterodyne Instrument for Planetary Wind And Composition (HIPWAC) interfaced with the 8.2 meter Subaru telescope of the National Astronomical Observatory of Japan. Retrieved wind velocities (approx.190 m/s at 230 km) from Doppler shifts of measured emission lines are compared to previous infrared heterodyne studies and compared to results front either direct wired measurements - Huygens Doppler Wind Experiment [5], Doppler shifts of reflected visible radiation [6], and mm-wave investigations [7]. Comparison to indirect wind retrievals from stellar occultation [8] observations and Cassini CIRS thermal maps [9] is also made, An empirical altitude-dependent wired model will be presented. The narrow ethane emission lines are analyzed to retrieve the ethane mole fraction and an attempt is made to evaluate the altitude distribution of ethane in the stratosphere for thermal profiles derived from measurements from Cassini and Huygens. Resultant ethane altitude distributions will be discussed and comparison to results front earlier HIPWAC and other remote sensing measurements and from contemporaneous Cassini/Huygens investigations [10, 11] will be made. Preliminary comparison suggests temporal or spatial variability in the line emission and retrieved ethane abundance in Titan's stratosphere:. Possible detection of minor hydrocarbon constituents and evidence of possible probing of Titan's mesosphere and of mesospheric wind shear will be discussed.

Kostiuk, T.↗

NASA NTRS1985

QUASAT: An orbiting very long baseline interferometer program using large space antenna systems

QUASAT, which stands for QUASAR SATELLITE, is the name given to a new mission being studied by NASA. The QUASAT mission concept involves a free flying Earth orbiting large radio telescope, which will observe astronomical radio sources simultaneously with ground radio telescopes. The primary goal of QUASAT is to provide a system capable of collecting radio frequency data which will lead to a better understanding of extremely high energy events taking place in a variety of celestial objects including quasars, galactic nuclei, interstellar masers, radio stars and pulsars. QUASAT's unique scientific contribution will be the increased resolution in the emission brightness profile maps of the celestial objects.

Jordan, J. F.↗

DOE OSTI2021

Optimization of the Observing Cadence for the Rubin Observatory Legacy Survey of Space and Time: A Pioneering Process of Community-focused Experimental Design

Vera C. Rubin Observatory is a ground-based astronomical facility under construction, a joint project of the National Science Foundation and the U.S. Department of Energy, designed to conduct a multipurpose 10 yr optical survey of the Southern Hemisphere sky: the Legacy Survey of Space and Time. Significant flexibility in survey strategy remains within the constraints imposed by the core science goals of probing dark energy and dark matter, cataloging the solar system, exploring the transient optical sky, and mapping the Milky Way. The survey’s massive data throughput will be transformational for many other astrophysics domains and Rubin’s data access policy sets the stage for a huge community of potential users. To ensure that the survey science potential is maximized while serving as broad a community as possible, Rubin Observatory has involved the scientific community at large in the process of setting and refining the details of the observing strategy. The motivation, history, and decision-making process of this strategy optimization are detailed in this paper, giving context to the science-driven proposals and recommendations for the survey strategy included in this Focus Issue.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

NASA NTRS1990

Planetary astronomy of Mars. Mars data reduction

Grant #NAGW-1408 was specifically awarded to obtain telescopic visible and near-IR spectral imaging of Mars during the 1988 apparition (9/28/88). The observing program was highly successful producing approximately 2 Gbytes of data, but was only funded for one year and virtually all of the funds were spent in data acquisition. The follow-up grant was funded the following year for reduction of these data into a scientifically productive form, which because of the size and nature of our observations, was a non-trivial task. A more detailed scientific analysis of these data (fully reduced) is in progress now and will take a number of years. Extended geologic analyses of the astronomical data are being funded by the NASA Planetary Geology and Geophysics program. The objective was to produce detailed reflectance spectra for contiguous, spatially resolved surface elements covering most of the planet (about +50 degrees to -90 degrees latitude, all longitudes). A total of 6 observing runs, of 3-4 days duration each, were conducted on the University of Arizona's 1.5m telescope on Mt. Bigelow. We present a sketch map showing the approximate total extent of our spectral image coverage. Nearly all of Mars south of 40 degrees N was observed at least once. About half of the area shown was observed multiple times. South of 65 degrees S, including the south polar cap, our coverage is heavily redundant. The first run was conducted June 29 - July 1, 1988 (all dates are UT) to serve as a baseline prior to possible dust storm activity on Mars. The other observing runs were closer to opposition: Sept. 3-6, 13-15, 24-26, and Oct. 5-7 and 16-18. The September and October observations were scheduled to provide maximum longitudinal coverage. This was also intended to provide a balance between surface observations and observations of predicted dust storm activity. No global dust storm developed in 1988, so we have a large volume of data for the surface of Mars.

Singer, Robert B.↗

NASA NTRS1995

Airborne spectrograph for the thermal IR: Broadband Array Spectrograph System

Spectroscopic studies in the 'fingerprint' region of the thermal IR from 3 to 14 microns of celestial dust components and the overall energy distribution of the sources are best served by moderate spectral resolution (R = lambda/Delta lambda approximately 30 to 200), high sensitivity observations. Spectral purity and the reproducibility of the spectral shape are critical as well, when using the spectral shape to assign temperatures to dust grains or to gas clouds based on the wavelength and shape of molecular bands. These sensor attributes are also important to the use of wavelengths and ratios of solid state features to derive compositions of dust grains in celestial sources. The advent of high quality linear arrays of blocked impurity band (BIB) detectors of Si:As permitted the development of a state-of-the-art, patented, cooled prism spectrograph. Developed at The Aerospace Corporation largely with in-house funds, the Broadband Array Spectrograph System (BASS) has been used for a variety of remote sensing applications, but especially for IR astronomical studies on the Kuiper Airborne Observatory and at the NASA Infrared Telescope Facility (IRTF). The attributes of the spectrograph, specifically having the pupil imaged onto the 2 linear 58 element detector arrays so that the effects of guiding errors are minimized, being able to maximally exploit the limited observing time by acquiring all 116 spectral channels simultaneously, and having all spectral channels imaged through the same aperture so that spectral mapping is readily and reliably accomplished, afford the scientist with a unique opportunity to conduct both surveys of examples of many different types of sources as well as in-depth studies of a given class of object by thoroughly sampling the class members. This duality was demonstrated with the BASS through a combination of KAO flights where spectral maps were obtained as part of in-depth studies of specific source regions (such as Orion and W3) and flights where up to 21 legs/flight were used to survey many different sources of different types.

Russell, Ray W.↗