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At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
NASA NTRS2017

The Detection of 6.9 µm Emission Features in the Infrared Spectra of IRAS 04296+3429, IRAS 05341+0852, IRAS 22272+5435: Evidence for the Presence of Hn-PAHs in Post AGB Stars

Polycyclic aromatic hydrocarbons (PAHs) are generally believed to be ubiquitous in space and responsible for numerous telltale interstellar infrared emission bands. In Sandford et al., (2013), we suggested that polycyclic aromatic hydrocarbons with excess hydrogenation at their periphery (Hn-PAHs) may be an important subclass of these molecules in some astrophysical environments. These molecules are candidates to explain objects with anomalously large 3.4 μm features, which are presumed to be associated with the aliphatic C—H stretching vibrations of the excess hydrogen. In that work, we suggest that for Hn-PAHs to be a viable candidate as the source for this 3.4 μm feature, we must also expect to observe methylene scissoring modes at 6.9 μm. In this work, we continue to develop the Hn-PAH hypothesis with a focus on the 6.9 μm feature. We also present some new observations of three post-asymptotic giant branch (post- AGB) objects with abnormally large 3.4 μm features, IRAS 04296+3429, IRAS 05341+0852, IRAS 22272+5435, in addition to one post-AGB object with normal PAH emissions, IRAS 20000+3239. These observations were made using the FORCAST instrument in grism mode on the Stratospheric Observatory for Infrared Astronomy (SOFIA) aircraft (Adams et al. 2010) and demonstrate the presence of a 6.9 μm feature for the three objects with abnormally large 3.4 μm features and no detectable 6.9 μm feature for the normal PAH emitter. These results are consistent with the hypothesis that Hn-PAHs are a possible source of these infrared emission bands.

ISM↗
NASA NTRS2004

The Far-Infrared Spectrum of Arp 220

ISO/LWS grating observations of the ultraluminous infrared galaxy Arp 220 shows absorption in molecular lines of OH, H 2 0 , CH, NH, and "3, well as in the [0 I] 63 pm line and emission in the [C 111 158 pm line. We have modeled the continuum and the emission/absorption of all observed features by means of a non-local radiative transfer code. The continuum from 25 to 1300 pm is modeled AS A WARM (106 K) NUCLEAR REGION THAT IS OPTICALLY THICK IN THE FAR-INFRARED, attenuated by an extended region (size 2") that is heated mainly through absorption of nuclear infrared radiation. The molecular absorption in the nuclear region is characterized by high excitation due to the high infrared radiation density. The OH column densities are high toward the nucleus and the extended region (about 2 x 10 sup 17 cm sup-2). The H2O column density is also high toward the nucleus (2 - 10 x 1017 cm-2) and lower in the extended region. The column densities in a halo that accounts for the absorption by the lowest lying levels are similar to what are found in the diffuse clouds toward the star forming regions in the Sgr B2 molecular cloud complex near the Galactic Center. Most notable are the high column densities found for NH and NH3 toward the nucleus, with values of about 1.5 x 10supl6 cmsup-2 and about 3 x 10supl6 cmsup-2, respectively, whereas the NH2 column density is lower than about 2 x 10sup15 cmsup-2. A combination of PDRs in the extended region and hot cores with enhanced H20 photodissociation and a possible shock contribution in the nuclei may explain the relative column densities of OH and H20, whereas the nitrogen chemistry may be strongly affected by cosmic ray ionization. The [C II] 158 pm line is well reproduced by our models and its "deficit" relative to the CII/FIR ratio in normal and starburst galaxies is suggested to be mainly a consequence of the dominant non-PDR component of far- infrared radiation, ALTHOUGH OUR MODELS ALONE CANNOT RULE OUT EXTINCTION EFFECTS IN THE NUCLEI.

Gonzalez-Alfonso, Eduardo↗
NASA NTRS2021

Deriving Deformable Mirror Performance Requirements in Simulation with Experimental Verification

Coronagraph instruments rely on predictable and stable deformable mirror (DM) surface displacement to achieve the contrast required to detect Earth-sized exoplanets orbiting nearby Solar-type stars. Anomalous DM behavior, such as unstable or pinned actuators, can limit contrast in coronagraphs. Simulating how these undesired behaviors affect the performance of a high contrast imaging architecture is important for developing requirements on their associated hardware. Simulating a vortex coronagraph (VC) with two deformable mirrors, this study quantifies how the number of pinned actuators affect the performance of Focal Plane Wavefront Sensing and Control algorithms using both Grid Search Electric Field Conjugation (EFC) and Planned EFC, which uses Beta-Bumping. The simulation also quantifies how various types of voltage noise such as zero-mean Gaussian noise, zero-mean periodic noise, and drift can affect the contrast of a VC during an observation run. A tolerance of a change in the Mean Normalized Intensity of ${1\times10^{-11}}$ is allocated to both types of error. If Planned EFC is used, only 1 pinned actuator on both DMs can be tolerated. If only pure Grid Search EFC is used the DMs cannot have any pinned actuators. For the case of zero-mean Gaussian noise and zero-mean periodic noise, one can tolerate a noise standard deviation of no more than ${\sigma = 0.45 \text{ mV}}$. For drift, we can only tolerate ${\sigma = 0.30 \text{ mV}}$ or less. These results show that the DM electronics and the DM themselves need to be nearly defect free to avoid having more than 1 pinned actuator. The electronics need to be tested for different types of noise statistics and that both the average and standard deviation of the noise should be measured.

Dean L. Palmer↗
NASA NTRS2014

The Neutron Star Zoo

Neutron stars are a very diverse population, both in their observational and their physical properties. They prefer to radiate most of their energy at X-ray and gamma-ray wavelengths. But whether their emission is powered by rotation, accretion, heat, magnetic fields or nuclear reactions, they are all different species of the same animal whose magnetic field evolution and interior composition remain a mystery. This article will broadly review the properties of inhabitants of the neutron star zoo, with emphasis on their high-energy emission. XXX Neutron stars are found in a wide variety of sources, displaying an amazing array of behavior. They can be isolated or in binary systems, accreting, heating, cooling, spinning down, spinning up, pulsing, flaring and bursting. The one property that seems to determine their behavior most strongly is their magnetic field strength, structure and evolution. The hot polar caps, bursts and flares of magnetars are likely due to the rapid decay and twisting of their superstrong magnetic fields, whose very existence requires some kind of early dynamo activity. The intermediate-strength magnetic fields of RPPs determines their spin-down behavior and radiation properties. However, the overlap of the magnetar and RPP populations is not understood at present. Why don't high-field RPPs burst or flare? Why don't lower-field magnetars sometimes behave more like RPPs? INS may be old magnetars whose high fields have decayed, but they do not account for the existence of younger RPPs with magnetar-strength fields. Not only the strength of the magnetic field but also its configuration may be important in making a NS a magnetar or a RPP. Magnetic field decay is a critical link between other NS populations as well. "Decay" of the magnetic field is necessary for normal RPPs to evolve into MSPs through accretion and spin up in LMXBs. Some kind of accretion-driven field reduction is the most likely mechanism, but it is controversial since it is not clear how effective it is or on what timescale a buried field might re-emerge. One piece of evidence in favor of accretion-driven field reduction is the fact that NSs in LMXBs, which are older systems (> 108 yr), have mostly low fields and NSs in HMXBs, which are younger systems (107 − 108 yr), have higher fields. This may be an indication that accretion-driven field reduction or decay has not had enough time to operate in HMXBs but has in LMXBs. However, there does not seem to be any evidence of decaying fields in either the LMXB or HMXB populations; e.g. smaller magnetic fields in older systems. On the other hand, CCOs are very young so if they acquired their low fields through mass fallback accretion, the field submergence would have had to operate on much faster timescales than it apparently does in LMXBs. But as we continue to find new species in the NS zoo, one of these may someday be the "Rosetta Stone" that will give us the clues for solving these puzzles.

Zoo↗
DOE OSTI2021

Constraining the nonanalytic terms in the isospin-asymmetry expansion of the nuclear equation of state

In this report we examine the properties of the isospin-asymmetry expansion of the nuclear equation of state from chiral two- and three-body forces. We focus on extracting the high-order symmetry energy coefficients that consist of both normal terms (occurring with even powers of the isospin asymmetry) as well as terms involving the logarithm of the isospin asymmetry that are formally nonanalytic around the expansion point of isospin-symmetric nuclear matter. These coefficients are extracted from numerically precise perturbation theory calculations of the equation of state coupled with a new set of finite difference formulas that achieve stability by explicitly removing the effects of higher-order terms in the expansion. We consider contributions to the symmetry energy coefficients from both two- and three-body interactions. It is found that the coefficients of the logarithmic terms are generically larger in magnitude than those of the normal terms from second-order perturbation theory diagrams, but overall the normal terms give larger contributions to the ground state energy. The high-order isospin-asymmetry terms are especially relevant at large densities where they affect the proton fraction in β-equilibrium matter, and in particular we find that at twice saturation density they can reduce the proton fraction by up to 0.02.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

The predicted properties of helium-enriched globular cluster progenitors at high redshift

Globular cluster progenitors may have been detected by Hubble Space Telescope, and are predicted to be observable with James Webb Space Telescope (JWST) and ground-based extremely large telescopes with adaptive optics. This has the potential to elucidate the issue of globular cluster formation and the origins of significantly helium-enriched subpopulations, a problem in Galactic astronomy with no satisfactory theoretical solution. Given this context, we use model stellar tracks and isochrones to investigate the predicted observational properties of helium-enriched stellar populations in globular cluster progenitors. We find that, relative to helium-normal populations, helium-enriched (ΔY = +0.12) stellar populations similar to those inferred in the most massive globular clusters, are expected, modulo some rapid fluctuations in the first ~30 Myr, to be brighter and redder in the rest frame. At fixed age, stellar mass, and metallicity, a helium-enriched population is predicted to converge to being ~0.40 mag brighter at $\lambda \approx 2.0\, {\mu \rm m}$, and to be 0.30-mag redder in the JWST–NIRCam colour (F070W - F200W), and to actually be fainter for $\lambda \lesssim 0.50 \, {\mu \rm m}$. Separately, we find that the time-integrated shift in ionizing radiation is a negligible $\sim \!5{{\ \rm per\ cent}}$, though we show that the Lyman-α escape fraction could end up higher for helium-enriched stars.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1983

Bed-rest studies - Fluid and electrolyte responses

Confinement in the horizontal position for 2 to 3 weeks results in a chronic decrease in plasma volume, increased interstitial fluid volume, and unchanged or slightly increased extracellular fluid volume. Concentrations of blood electrolytes, glucose, and nitrogenous constituents remain within normal limits of variability when maintenance levels of isometric or isotonic exercise are performed for 1 hr/day. Hematocrit and plasma osmolality can be elevated significantly throughout bed rest (BR). Significant diuresis occurs on the first day, and increases in urine Na and Ca continue throughout BR, although voluntary fluid intake is unchanged. Urine Na and K are evaluated during the second week of BR in spite of stabilization of PV and extracellular volume. The initial diuresis probably arises from extracellular fluid while subsequent urine loss above control levels must come from the intracellular fluid. Preservation of the extracellular volume takes precedance over maintenance of the intracellular fluid volume. The functioning of a natriuretic factor (hormone) to account for the continued increased loss of Na in the urine is suggested. Previously announced in STAR as N83-24160

Greenleaf, J. E.↗
NASA NTRS1989

Sources of error in thematic classification of remotely sensed imagery

From a statistician's point of view, the input datasets are rarely examined to determine their underlying frequency distribution; it is just assumed that the data are normal enough, and that the deviations from normality are unimportant. It is not clear how deviations from a hypothetical multivariate normal might affect the power of the classification process, and there is ample evidence in the literature that, at a minimum, the spectral channels are correlated. From a practioner's point of view, in a supervised classification the number of training fields for developing a statistical description of a given class is usually arbitrary. It is unclear how small changes in the details of the training field selection process affect the quality of the derived thematic information. The start of an examination of this latter problem is discussed.

Star, Jeffrey L.↗
NASA NTRS1992

Ultraviolet, optical, and infrared observations of the high-latitude molecular cloud toward HD 210121

Low-resolution UV spectra of the B3 V star HD 210121, located behind the high-latitude molecular cloud DBB 80, yield an extinction curve exhibiting a far-UV rise that is among the steepest known. The apparently simple line of sight affords an excellent opportunity for investigating the absorption and emission characteristics of a single, isolated interstellar cloud characterized by extreme UV extinction. The low ratios of the IRAS bands with respect to I(100 microns) suggest that the radiation field incident on the cloud is lower than the average interstellar field, with further attenuation of the field within the cloud. The apparent relative enhancement of I(12 microns) compared with models of dust emission, and the extremely steep far-UV extinction together are consistent with the presence of an enhanced population of very small grains; the normal calcium depletion suggests that there has been little wholesale grain destruction. The steep far-UV extinction may help to explain the relatively high abundances of CO and CN. The disagreement in density for this cloud inferred from C2 absorption versus that inferred from CO emission may be due in part to clumping in the gas sample by the radio beams.

Welty, Daniel E.↗
DOE OSTI2020

Stellar Mass and Stellar Mass-to-light Ratio–Color Relations for Low Surface Brightness Galaxies

We estimate the stellar mass for a sample of low surface brightness galaxies (LSBGs) by fitting their multiband spectral energy distributions (SEDs) to the stellar population synthesis model. The derived stellar masses (log M {sub *}/M {sub ⊙}) span from 7.1 to 11.1, with a mean of log M {sub *}/M {sub ⊙} = 8.5, which is lower than that for normal galaxies. The stellar mass-to-light ratio (γ*) in each band varies little with the absolute magnitude but increases with higher M {sub *}. This trend of γ* with M {sub *} is even stronger in bluer bands. In addition, the γ* for our LSBGs slightly declines from the r band to the longer-wavelength bands. The log γ{sub ∗}{sup j} (j = g, r, i, and z) have relatively tight relations with optical colors of g − r and g − i. Compared with several representative γ*–color relations (MLCRs) from the literature, our MLCRs based on LSBG data are consistently among those literature MLCRs previously defined on diverse galaxy samples, and the existing minor differences between the MLCRs are caused by the differences in the SED model ingredients (including initial mass function, star formation history, and stellar population model), line fitting techniques, galaxy samples, and photometric zero-point, rather than the galaxy surface brightness itself, which distinguishes LSBGs from high surface brightness galaxies. Our LSBGs would be very likely to follow those representative MLCRs previously defined in diverse galaxy populations, if those main ingredients were taken into account.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1980

A process of stellar nucleosynthesis which mimicks mass fractionation in P-xenon

The combination of the O-shell theory of Heymann and Dziczkaniec and the supernova theory of Woosley and Howard clearly identifies the astrophysical sites for the formation of the anomalous light Xe component in carbonaceous chondrites. These sites are the O- and Ne-shells, and possibly C-shell of a massive star. Most of the Xe-124 and Xe-126 are formed in the O-shell during hydrostatic core silicon-burning, when a seed of heavy nuclei is exposed to an effective temperature near T9 = 2.0. Xe-128 is formed via Ba-128 in the O-shell, but the amounts appear too small to satisfy the deduced Xe-128/Xe-124 and Xe-128/Xe-126 yield ratios from the chondrites. However, substantial amounts of Xe-128 can be formed in the adjacent Ne- and C-shells during the explosion. The formation of Ba-128 in the O-shell would increase if the (gamma, alpha) photodisintegration rate in Ba-128 is actually smaller than calculated by Woosley and Howard. Lewis et al. have proposed that the anomalous light Xe component is mass-fractionated normal Xe. It is in this sense that the process of stellar nucleosynthesis of the present paper mimicks mass-fractionation.

Heymann, D.↗
DOE OSTI2026

The high level trigger and express data production at STAR

To meet the demands of the Beam Energy Scan phase-II (BES-II) program, the STAR experiment at the Relativistic Heavy Ion Collider (RHIC) developed a dual real-time framework consisting of a High Level Trigger (HLT) and an Express Data Production system (xProduction). The HLT operates online within the Data Acquisition (DAQ) chain on a dedicated multi-core CPU cluster with the option to offload compute-intensive kernels to Xeon Phi coprocessors. It uses parallelized algorithms, such as the Cellular Automaton (CA) Track Finder, to perform rapid tracking, vertexing, and event filtering. This allows it to select events of interest in real time and provide immediate feedback on detector and beam conditions. In contrast, the xProduction workflow runs concurrently and independently of the DAQ loop. It applies near offline-quality calibration and reconstruction within hours of data collection. The xProduction input is the express data stream, whose content can be enriched by HLT trigger/priority selections under DAQ/HLT resource constraints, and it uses the STAR calibration/conditions framework, incorporating online calibration/QA information when available. This enables early preliminary physics analysis, including the reconstruction of rare signals, such as hyperons and hypernuclei. It also provides collaboration-wide access to analysis-ready datasets. Together, the HLT and xProduction systems form a complementary architecture: the HLT performs online event selection while the xProduction chain delivers high-quality results within a short amount of time. This integrated framework has enabled the prompt reconstruction of the $^5_Λ$ He hypernucleus with high statistical significance and the efficient processing of hundreds of millions of heavy-ion collision events. In conclusion, its demonstrated scalability and robustness establish a model for future high-luminosity experiments requiring both online event filtering and rapid access to analysis-quality data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1993

Powering the superwind in NGC 253

NGC 253 is a prototypical moderate nuclear starburst galaxy. It is a barred SBc spiral galaxy at a distance of approximately 3 Mpc and can be studied on scales down to 15 pc in the optical and near IR. It is a bright IRAS source with a flux of 1000 Jy at 60 microns and a FIR luminosity of 3 x 10(exp 10) solar luminosity. It has a strong Br(gamma) emission line, a signature of ongoing massive star formation and deep CO absorption bands, which are indicative of the dominance of red supergiants in the near IR. It contains a population of compact radio sources, similar to those seen in M82. Optical spectra show that the nucleus is heavily reddened, with a Balmer decrement of approximately 30. NGC 253 possesses a 'superwind,' seen both in x-ray emission and in optical line emission. Nuclear ejection was first suggested to explain the kinematics of the nuclear region. We have obtained J, H, and K images of the entire galaxy at 1.3 arcsec/pixel (18 pc/pixel) using the superconducting quantum interference device (SQUID) on the KPNO 1.3 m. We have constructed a mosaic of 180 s exposures which traces the galaxy over much of its optical extent. The data were shifted, rotated, magnified, and calibrated following normal practice.

Watson, Alan↗
NASA NTRS1994

In-flight scale/distortion calibration of the Hubble Space Telescope fixed-head star trackers

This paper describes an in-flight scale and distortion calibration procedure that has been developed for the Ball Aerospace Systems Division Fixed-Head Star Trackers (FHST's) used on the Hubble Space Telescope (HST). The FHST is a magnetically focused and deflected imaging sensor that is designed to track stars as faint as m(sub v) = 5.7 over an 8 degree by 8 degree field of view. Raw FHST position measurements are accurate to approximately 200 arcseconds, but this can be improved to 10-15 arcseconds by processing the raw measurements through calibration polynomials that correct for flat field, temperature intensity, and magnetic field effects. The coefficients for these polynomials were initially determined using ground test data. On HST the use of three FHST's is an integral part of the preliminary attitude update procedures required before the acquisition of guide stars for science observations. To this end, FHST-based attitude determination having single-axis errors no worse than 22 arcseconds (1 sigma) is required. In early 1991 it became evident that one of the HST FHST's was experiencing a significant change in its optical scale. By mid-1993 the size of this error had grown to a point that, if not corrected, it would correspond to a maximum position error on the order of 100 arcseconds. Subsequent investigations demonstrated that substantial, uncompensated cubic distortion effects had also developed, the maximum contribution to position errors from the cubic terms being on the order of 30 arcseconds. To ensure accurate FHST-based attitude updates, procedures have been developed to redetermine the FHST scale and distortion calibration coefficients based on in-flight data gathered during normal HST operations. These scale and distortion calibrations have proven very effective operationally, and procedures are in place to monitor FHST calibration changes on a continuing basis.

Mccutcheon, R.↗
NASA NTRS1990

Cooling flows and X-ray emission in early-type galaxies

The X-ray properties of normal early-type galaxies and the limited theoretical understanding of the physics of the hot interstellar medium in these galaxies are reviewed. A number of simple arguments about the physical state of the gas are given. Steady-state cooling flow models for these galaxies are presented, and their time-dependent evolution is discussed. The X-ray emission found in early-type galaxies indicates that they contain significant amounts of hot interstellar gas, and that they are not the gas-poor systems they were previously thought to be. In the brighter X-ray galaxies, the amounts of hot gas observed are consistent with those expected given the present rates of stellar mass loss. The required rates of heating of the gas are consistent with those expected from the motions of gas-losing stars and supernovae. The X-ray observations are generally more consistent with a lower rate of Type I supernovae than was previously thought.

Sarazin, Craig L.↗
NASA NTRS2006

Difficulties in Laboratory Studies and Astronomical Observations of Organic Molecules: Hydroxyacetone and Lactic Acid

For the past 35 years, radio astronomy has revealed a rich organic chemistry in the interstellar gas, which is exceptionally complex towards active star-forming regions. New solar systems condense out of this gas and may influence the evolution of life on newly formed planets. Much of the biologically important functionality is present among the some 130 gas-phase molecules found to date, including alcohols, aldehydes, ketones, acids, amines, amides and even the simplest sugar - glycolaldehyde. Still, many unidentified interstellar radio signals remain, and their identification relies on further laboratory study. The molecules hydroxyacetone and lactic acid are relatively small organic molecules, but possess rather complex rotational spectra owing to their high asymmetry. Hydroxyacetone is particularly problematic because it possess a very low barrier to internal rotation, and exhibits strong coupling of the free-rotor states with the overall rotation of the molecule. As in the case of acetamide, a full decomposition method was employed to order the resultant eigenstates onto normal asymmetric top eigenvectors.

Apponi, A. J.↗
NASA NTRS2010

Large Telescope Segmented Primary Mirror Alignment

A document discusses a broadband (white light) point source, located at the telescope Cassegrain focus, which generates a cone of light limited by the hole in the secondary mirror (SM). It propagates to the aspheric null-mirror, which is optimized to make all the reflected rays to be normal to the primary mirror (PM) upon reflection. PM retro-reflects the rays back through the system for wavefront analysis. The point source and the wavefront analysis subsystems are all located behind the PM. The PM phasing is absolute (white light) and does not involve the SM. A relatively small, aspheric null-mirror located near the PM center of curvature has been designed to deliver the high level of optical wavefront correction. The phasing of the segments is absolute due to the use of a broadband source. The segmented PM is optically aligned independently and separately from the SM alignment. The separation of the PM segments alignment from the PM to the SM, and other telescope optics alignments, may be a significant advantage, eliminating the errors coupling. The point source of this concept is fully cooperative, unlike a star or laser-generated guide-star, providing the necessary brightness for the optimal S/N ratio, the spectral content, and the stable on-axis position. This concept can be implemented in the lab for the PM initial alignment, or made to be a permanent feature of the space-based or groundbased telescope.

Rud, Mayer↗
NASA NTRS1998

A2111: A z= 0.23 Butcher-Oemler Cluster with a Non-Isothermal Atmosphere and Normal Metallicity

We report results from an x-ray spectral study of the z=0.23 Abell 2111 galaxy cluster using the Advanced Satellite for Astrophysics and Cosmology and the ROSAT Position Sensitive Proportional Counter. By correcting for the energy-dependent point-spread function of the instruments, we have examined the temperature structure of the cluster. The cluster's core within 3 is found to have a temperature of 5.4 +/- 0.5 keV, significantly higher than 2.8 +/-0.7 keV in the surrounding region of r = 3-6. This radially decreasing temperature structure can be parameterized by a polytropic index of gamma less than 1.4. Furthermore, the intracluster medium appears clumpy on scales less than 1. Early studies have revealed that the x-ray centroid of the cluster shifts with spatial scale and the overall optical and x-ray morphology is strongly elongated. These results together suggest that A2111 in undergoing a merger, which is likely responsible for the high fraction of blue galaxies observed in the cluster. We have further measured the abundance of the medium as 0.25 +/- 0.14 solar. This value is similar to those of nearby clusters which do not show a large blue galaxy function, suggesting that star formation in disk galaxies and subsequent loss to the intracluster medium do not drastically alter the average abundance of a cluster since z=0.23.

Wang, Q. Daniel↗