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At least 1,171 records · Page 65
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Development and operations of the astrophysics data system

Abstract service - Continued regular updates of abstracts in the databases, both at SA0 and at all mirror sites. - Modified loading scripts to accommodate changes in data format (PhyS) - Discussed data deliveries with providers to clear up problems with format or other errors (EGU) - Continued inclusion of large numbers of historical literature volumes and physics conference volumes xeroxed from the library. - Performed systematic fixes on some data sets in the database to account for changes in article numbering (AGU journals) - Implemented linking of ADS bibliographic records with multimedia files - Debugged and fixed obscure connection problems with the ADS Korean mirror site which were preventing successful updates of the data holdings. - Wrote procedure to parse citation data and characterize an ADS record based on its citation ratios within each database.

Murray, Stephen S.↗
NASA NTRS2006

Computational Spectroscopy of Polycyclic Aromatic Hydrocarbons In Support of Laboratory Astrophysics

Polycyclic aromatic hydrocarbons (PAHs) are strong candidates for the molecular carriers of the unidentified infrared bands (UIR) and the diffuse interstellar bands (DIBs). In order to test the PAH hypothesis, we have systematically measured the vibronic spectra of a number of jet-cooled neutral and ionized PAHs in the near ultraviolet (UV) to visible spectral ranges using the cavity ring-down spectroscopy. To support this experimental effort, we have carried out theoretical studies of the spectra obtained in our measurements. Ab initio and (time-dependent) density.functiona1 theory calculations are performed to obtain the geometries, energetics, vibrational frequencies, transition dipole moments, and normal coordinates of these PAH molecules. Franck-Condon (FC) calculations and/or vibronic calculations are then performed using the calculated normal coordinates and vibrational frequencies to simulate the vibronic spectra. It is found that vibronic interactions in these conjugated pi electron systems are often strong enough to cause significant deviations from the Born-Oppenheimer (BO) approximation. For vibronic transitions that are well described by the BO approximation, the vibronic band profiles are simulated by calculating the rotational structure of the vibronic transitions. Vibronic oscillator strength factors are calculated in the frame of the FC approximation from the electronic transition dipole moments and the FC factors. This computational effort together with our experimental measurements provides, for the first time, powerful tools for comparison with space-based data and, hence, a powerful approach to understand the spectroscopy of interstellar PAH analogs and the nature of the UIR and DIBs.

Tan, Xiaofeng↗
NASA NTRS1996

Jet Propulsion Laboratories in Space: The Production of Astrophysical Jets by Magnetic Accretion Disks, and a Super-Eddington Wind Model for the Early Stages of GROJ1455-40

Measurements of the properties of gravitational lenses have the power to tell us what sort of universe we live in. The brightest known radio Einstein ring/gravitational lens PKS 1830-211, whilst obscured by our galaxy at optical wavelengths, has recently provided a lensing galaxy redshift of 0.89 through the detection of a new absorption feature, most likely due to neutral hydrogen in a second redshift system at z=0.19.

PKS 1830-211↗
NASA NTRS1995

Astrophysics with Pulsar/Main Sequence Star Binaries

Until very recently, all known radio pulsars in binary orbits had as companions old, degenerate stars, either neutron stars or white dwarfs. In this talk we introduce a new class of binary radio pulsars having as companions young, massive stars. Concentrating on one system in particular, we show that these systems open a new phase space for studying a variety of physical phenomena, including post-Keplerian dynamics, physics of stellar winds and interiors, and binary evolution theory.

Arecibo Telescope↗
NASA NTRS1994

Active Refrigeration for Space Astrophysics Missions

The use of cryogen dewars limits mission lifetime, increases sensor mass, and increases program engineering and launch costs on spacebased low-background, precision-pointing instruments, telescopes and interferometers.

mechanical and sorption coolers cryogenic radiator↗
NASA NTRS2006

A Model Study of the Thermal Evolution of Astrophysical Ices

We address the question of the evolution of ices that have been exposed to radiation from stellar sources and cosmic rays. We studied in the laboratory the thermal evolution of a model ice sample: a mixture of water, hydrogen peroxide, dioxygen, and ozone produced by irradiating solid H2O2 with 50 keV H(+) at 17 K. The changes in composition and release of volatiles during warming to 200 K were monitored by infrared spectroscopy, mass spectrometry, and microbalance techniques. We find evidence for voids in the water component from the infrared bands due to dangling H bonds. The absorption from these bands increases during heating and can be observed at temperatures as high as approx. 155 K. More O2 is stored in the radiolyzed film than can be retained by codeposition of O2 and H2O. This O2 remains trapped until approx. 155 K, where it desorbs in an outburst as water ice crystallizes. Warming of the ice also drastically decreases the intrinsic absorbance of O2 by annealing defects in the ice. We also observe loss of O3 in two stages during heating, which correlates with desorption and possibly chemical reactions with radicals stored in the ice, triggered by the temperature increase.

Loeffler, M. J.↗
NASA NTRS2006

The Homunculus: a Unique Astrophysical Laboratory

eta Car is surrounded by bipolar shells, the Homunculus and the internal Little Homunculus, that are observed in both emission and absorption. Thin disks, located between the bipolar lobes, include the very bright Weigelt blobs and the neutral emission structure called the Strontium filament. All are affected by changes in UV and X-Ray flux of the binary system. For example, the normally ionized Little Homunculus recombines during the few month long spectroscopic minimum and then reionizes. Spectral data, obtained with Hubble Space Telescope/Space Telescope Imaging Spectrograph (HST/STIS) and with Very Large Telescope/UltraViolet Echelle Spectrograph (VLT/UVES), provide a wealth of information on spectroscopic properties of neutral and singly-ionized metals and on chemistry of nitrogen rich, carbon, oxygen poor, dense, warm gas. This information is important to understand gamma ray bursters (GRB) that reveal red-shifted near-UV metallic absorptions from pre-GRB stellar ejecta.

Gull, T. R.↗
NASA NTRS2006

THz Spectroscopy and Spectroscopic Database for Astrophysics

Molecule specific astronomical observations rely on precisely determined laboratory molecular data for interpretation. The Herschel Heterodyne Instrument for Far Infrared, a suite of SOFIA instruments, and ALMA are each well placed to expose the limitations of available molecular physics data and spectral line catalogs. Herschel and SOFIA will observe in high spectral resolution over the entire far infrared range. Accurate data to previously unimagined frequencies including infrared ro-vibrational and ro-torsional bands will be required for interpretation of the observations. Planned ALMA observations with a very small beam will reveal weaker emission features requiring accurate knowledge of higher quantum numbers and additional vibrational states. Historically, laboratory spectroscopy has been at the front of submillimeter technology development, but now astronomical receivers have an enormous capability advantage. Additionally, rotational spectroscopy is a relatively mature field attracting little interest from students and funding agencies. Molecular data base maintenance is tedious and difficult to justify as research. This severely limits funding opportunities even though data bases require the same level of expertise as research. We report the application of some relatively new receiver technology into a simple solid state THz spectrometer that has the performance required to collect the laboratory data required by astronomical observations. Further detail on the lack of preparation for upcoming missions by the JPL spectral line catalog is given.

Pearson, John C.↗
NASA NTRS2006

Laboratory astrophysics on ASDEX Upgrade: Measurements and analysis of K-shell O, F, and Ne spectra in the 9 - 20 A region

High-resolution measurements of K-shell emission from O, F, and Ne have been performed at the ASDEX Upgrade tokamak in Garching, Germany. Independently measured temperature and density profiles of the plasma provide a unique test bed for model validation. We present comparisons of measured spectra with calculations based on transport and collisional-radiative models and discuss the reliability of commonly used diagnostic line ratios.

Hansen, S. B.↗
NASA NTRS2006

A Brief Summary of Some of the Laboratory Astrophysics Workshop

Our present knowledge of the molecular universe has come primarily from radio observations [ I include here millimeter and submillimeter in this rubric]. There are a number of reasons for this but the primary one is the extremely high spectral resolution. The ease of observing emission from the volume of dense molecular clouds without significant attenuation by scattering from dust has shown this to be the powerful observational tool for molecular astronomy. Finally the relative simplicity of rotational compared to vibrational or electronic spectroscopy allows carrier identification as well as facile evaluation of cloud conditions such as density and temperature. These virtues become tenuous as the astronomical observations are pushed to higher frequencies for enhanced observational sensitivity. Thus precision rest frequencies are mandatory for the search for new species. We may inquire about which new species require particular attention, and which species may be relatively safely predicted on the basis of lower frequency laboratory measurements. For a rigid rotor the three rotational constants are sufficient to completely specify the transition frequencies. The intensities require the three components of the electric dipole moment. For semirigid species, where the centrifugal distortion, may be treated at the quartic level of angular momentum (Bunker et al. 1998), up to five additional constants are required (Watson 1967). There are a number of such species of considerable interest, where laboratory measurements are adequate for astronomical searches.

Klemperer, William↗
NASA NTRS2006

The Evolution of Dust in Extreme Astrophysical Environments

The recent discovery of QSOs located at redshift z greater than 6, with high infrared luminosities (typically 1.E13 solar luminosities), challenges our understanding of dust evolution. Indeed, these high infrared luminosities imply more than 1.E8 solar masses of dust and nearly solar gas-to-dust mass ratios. An interesting question is how do we make so much dust within approx. 400 Myr, which is roughly the age of the galaxy assuming it formed at z-10. During this epoch, AGB stars could not have enriched the ISM, so that all the dust must have formed by supernovae (SN). However, SN blast waves also play an important role in destroying the dust in the ISM. Understanding the formation and evolution of the dust in such objects requires therefore the construction of a detailed model for the chemical evolution of the gas and dust phases of the ISM. We focus on the well-studied quasar SDSS J1148+5251, at z=6.42. Using the IR luminosities as tracers of of the star formation rate (SFR) in these objects implies a rates of 3E3 Msun/yr, and SN rates of about 200/yr. However, this quasar contains an embedded AGN, so that the IR luminosity may not be a good tracer of the SFR in this object. Using the estimated mass of gas as a tracer of the SFR we construct a self-consistent model for the evolution of interstellar dust, which also follows the formation and destruction of the dust by SN. Finally, we discuss the contribution of the AGN to the total infrared luminosity, and its implications for the mass of the black hole that is required to power the observed IR emission.

Dwek, Eli↗
NASA NTRS2006

Eta Carinae and the Homunculus: An Astrophysical Laboratory

High spatial resolution spectroscopy with HST/STIS between 1998.0 and 2004.2 has provided much exciting information about the central binary system and the physics of its N-rich, C,O-poor ejecta. Stellar He I profiles, noticeably blue-shifted relative to P Cygni H and Fe II line profiles, originate from the ionized wind region between two massive companions. Changes in profiles of He I singlet and triplet lines provide clues to the excitation mechanisms involved as the hot, UV companion moves in its highly eccentric orbit. For 90% of the 5.54-year period, the spectra of nearby Weigelt blobs and the Little Homunculus include highly excited emission lines of Ar, Ne, and Fe. During the few month-long spectroscopic minimum, these systems are deprived of Lyman continuum. Recombination, plus cooling, occurs. In the skirt region between the bipolar Homunculus, a neutral emission region, devoid of hydrogen emission, glows in Ti II, Fe I, Sr II, Sc II, etc. We find the ejecta to have Ti/Ni abundances nearly 100 times solar, not due to nuclear processing, but due to lack of oxygen. Many metals normally tied up in interstellar dust remain in gaseous phase. Much information is being obtained on the physical processes in these warm N-rich gases, whose excitation varies with time in a predictable pattern. Indeed recent GRB high dispersion spectra include signatures of circumGRB warm gases. This indicates that the early, primordial massive stars have warm massive ejecta reminiscent to that around Eta Carinae.

Gull, Theodore R.↗
NASA NTRS2006

General Astrophysics with TPF: Not Just Dark Energy

Besides searching for Earth-LIke Planets, TPF can study Jupiters, Neptunes, and all sorts of exotic planets. It can image debris-disks, YSO disks, AGN disks, maybe even AGB disks. And you are probably aware that a large optical space telescope like TPF-C or TPF-O can be a fantastic tool for studying the equation of state of the Dark Energy. I will review some of the future science of TPF-C, TPF-I and TPF-O, focusing on the applications of TPF to the study of objects in our Galaxy: especially circumstellar disks and planets other than exo-Earths.

Kuchner, Marc↗
NASA NTRS2007

Testing Special Relativity at High Energies with Astrophysical Sources

Since the group of Lorentz boosts is unbounded, there is a question as to whether Lorentz invariance (LI) holds to infinitely short distances. However, special and general relativity may break down at the Planck scale. Various quantum gravity scenarios such as loop quantum gravity, as well as some forms of string theory and extra dimension models may imply Lorentz violation (LV) at ultrahigh energies. The Gamma-Ray Large Area Space Telescope (GLAST), to be launched in mid-December, will measure the spectra of distant extragalactic sources of high energy gamma-rays, particularly active galactic nuclei and gamma-ray bursts. GLAST can look for energy-dependent gamma-ray propagation effects from such sources as a signal of Lorentz invariance violation. These sources may also exhibit the high energy cutoffs predicted to be the result of intergalactic annihilation interactions with low energy photons having a flux level as determined by various astronomical observations. With LV the threshold for such interactions can be significantly raised, changing the predicted absorption turnover in the observed spectrum of the sources. Stecker and Glashow have shown that the existence such absorption features in the spectra of extragalactic sources puts constraints on LV. Such constraints have important implications for some quantum gravity and large extra dimension models. Future spaceborne detectors dedicated to measuring gamma-ray polarization can look for birefringence effects as a possible signal of loop quantum gravity. A very small LV may also result in the modification or elimination of the GZK effect, thus modifying the spectrum of ultrahigh energy cosmic rays. This possibility can be explored with ground-based arrays such as Auger or with a space based detector system such as the proposed OWL satellite mission.

Stecker, F. W.↗