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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,189 records · Page 66
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

THE WIDEST-SEPARATION SUBSTELLAR COMPANION CANDIDATE TO A BINARY T TAURI STAR

The results of near-infrared imaging and spectroscopy of a substellar companion (SR12 C), with a possible planetary mass, of a binary T Tauri star (SR12 AB) in the {rho} Ophiuchi star-forming region are presented. The object is separated by {approx}8.''7, corresponding to {approx}1100 AU at 125 pc, and has an H-band brightness of 15.2 mag and infrared spectra suggesting a spectral type of M9.0 {+-} 0.5. It is confirmed that SR12 C is physically related to the {rho} Ophiuchi star-forming region from its common proper motion with SR12 AB and its youth is confirmed by a gravity-sensitive spectral feature. Furthermore, based on the number of known members of the {rho} Ophiuchi star-forming region in the area in which SR12 AB exists, the probability of a chance alignment is {approx}1% and it is therefore likely that SR12 C is physically associated with SR12 AB. The mass of SR12 C is estimated by comparing its estimated luminosity and assumed age with the theoretical age-luminosity relation. SR12 C is identified as an extremely low-mass (0.013 {+-} 0.007 M{sub sun}) object, but its separation from its parent star is the widest among planetary-mass companion (PMC) candidates imaged to date. In addition, SR12 C is the first PMC candidate directly imaged around a binary star. This discovery suggests that PMCs form via multiple star formation processes including disk gravitational instability and cloud core fragmentation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

A NEW SAMPLE OF VERY MASSIVE STAR FORMING COMPLEXES IN THE SPITZER GLIMPSE SURVEY

We examine the 13 most luminous sources in the WMAP free-free map using the Spitzer GLIMPSE and Midcourse Space Experiment surveys to identify massive star formation complexes, emitting one-third of the Galactic free-free luminosity. We identify star-forming complexes (SFCs) by a combination of bubble morphology in 8 {mu}m emission and radio recombination line radial velocities. We find 40 SFCs associated with our WMAP sources and determine unique distances up to 31. We interpret the bubbles as evidence for radial expansion. The radial velocity distribution for each source allows us to measure the intrinsic speed of a complex's expansion. This speed is consistent with the size and age of the bubbles. The high free-free luminosities, combined with negligible synchrotron emission, demonstrate that the bubbles are not driven by supernovae. The kinetic energy of the largest bubbles is a substantial fraction of that measured in the older superbubbles found by Heiles. We find that the energy injected into the interstellar medium by our bubbles is similar to that required to maintain turbulent motion in the gas disk inside 8 kpc. We report a number of new SFCs powered by massive (M{sub *} > 10{sup 4} M{sub sun}) star clusters. We measure the scale height of the Galactic O stars to be h{sub *} = 35 {+-} 5 pc. We determine an empirical relationship between the 8 {mu}m and free-free emission of the form F {sub 8{mu}m} {proportional_to} F {sup 2}{sub ff}. Finally, we find that the bubble geometry is more consistent with a spherical shell rather than a flattened disk.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

THERMAL STABILITY OF MAGNETIZED, OPTICALLY THIN, RADIATIVE COOLING-DOMINATED ACCRETION DISKS

We investigate the thermal stability of optically thin, two-temperature, radiative cooling-dominated accretion disks. Our linear analysis shows that the disk is thermally unstable without magnetic fields, which agrees with previous stability analysis on the Shapiro-Lightman-Eardley disk. By taking into account the effects of magnetic fields, however, we find that the disk can be, or partly be, thermally stable. Our results may be helpful to understand the outflows in optically thin flows. Moreover, such radiative cooling-dominated disks may provide a new explanation of the different behaviors between black hole and neutron star X-ray binaries on the radio/X-ray correlation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

HIGH-RESOLUTION CO OBSERVATION OF THE CARBON STAR CIT 6 REVEALING THE SPIRAL STRUCTURE AND A NASCENT BIPOLAR OUTFLOW

CIT 6 is a carbon star in the transitional phase from the asymptotic giant branch (AGB) to the protoplanetary nebulae (pPNs). Observational evidences of two point sources in the optical, circumstellar arc segments in an HC{sub 3}N line emission, and a bipolar nebula in near-infrared provide strong support for the presence of a binary companion. Hence, CIT 6 is very attractive for studying the role of companions in the AGB–pPN transition. We have carried out high-resolution {sup 12}CO J = 2–1 and {sup 13}CO J = 2–1 observations of CIT 6 with the Submillimeter Array combined with the Submillimeter Telescope (single-dish) data. The {sup 12}CO channel maps reveal a spiral-shell pattern connecting the HC{sub 3}N segments in a continuous form and an asymmetric outflow corresponding to the near-infrared bipolar nebula. Rotation of the {sup 12}CO channel peak position may be related to the inner spiral winding and/or the bipolar outflow. An eccentric orbit binary is suggested for the presence of an anisotropic mass loss to the west and a double spiral pattern. The lack of interarm emission to the west may indicate a feature corresponding to the periastron passage of a highly eccentric orbit of the binary. Spatially averaged radial and spectral profiles of {sup 12}CO J = 2–1 and {sup 13}CO J = 2–1 are compared with simple spherical radiative transfer models, suggesting a change of {sup 12}CO/{sup 13}CO abundance ratio from ∼30 to ∼50 inward in the CSE of CIT 6. The millimeter continuum emission is decomposed into extended dust thermal emission (spectral index ∼ −2.4) and compact emission from radio photosphere (spectral index ∼ −2.0)

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

SUPERNOVA CONSTRAINTS AND SYSTEMATIC UNCERTAINTIES FROM THE FIRST THREE YEARS OF THE SUPERNOVA LEGACY SURVEY

We combine high-redshift Type Ia supernovae from the first three years of the Supernova Legacy Survey (SNLS) with other supernova (SN) samples, primarily at lower redshifts, to form a high-quality joint sample of 472 SNe (123 low-z, 93 SDSS, 242 SNLS, and 14 Hubble Space Telescope). SN data alone require cosmic acceleration at >99.999% confidence, including systematic effects. For the dark energy equation of state parameter (assumed constant out to at least z = 1.4) in a flat universe, we find w = -0.91{sup +0.16} {sub -0.20}(stat){sup +0.07} {sub -0.14}(sys) from SNe only, consistent with a cosmological constant. Our fits include a correction for the recently discovered relationship between host-galaxy mass and SN absolute brightness. We pay particular attention to systematic uncertainties, characterizing them using a systematic covariance matrix that incorporates the redshift dependence of these effects, as well as the shape-luminosity and color-luminosity relationships. Unlike previous work, we include the effects of systematic terms on the empirical light-curve models. The total systematic uncertainty is dominated by calibration terms. We describe how the systematic uncertainties can be reduced with soon to be available improved nearby and intermediate-redshift samples, particularly those calibrated onto USNO/SDSS-like systems.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

A CHANDRA ACIS STUDY OF THE YOUNG STAR CLUSTER TRUMPLER 15 IN CARINA AND CORRELATION WITH NEAR-INFRARED SOURCES

Using the highest-resolution X-ray observation of the Trumpler 15 star cluster taken by the Chandra X-ray Observatory, we estimate the total size of its stellar population by comparing the X-ray luminosity function (XLF) of the detected sources to a calibrator cluster and identify for the first time a significant fraction ({approx}14%) of its individual members. The highest-resolution near-IR observation of Trumpler 15 (taken by the HAWK-I instrument on the Very Large Telescope) was found to detect most of our X-ray selected sample of cluster members, with a K-excess disk frequency of 3.8% {+-} 0.7%. The near-IR data, XLF, and published spectral types of the brightest members support a cluster age estimate (5-10 Myr) that is older than those for the nearby Trumpler 14 and Trumpler 16 clusters, and suggest that high-mass members may have already exploded as supernovae. The morphology of the inner {approx}0.7 pc core of the cluster is found to be spherical. However, the outer regions (beyond {approx}2 pc) are elongated, forming an 'envelope' of stars that, in projection, appears to connect Trumpler 15 to Trumpler 14; this morphology supports the view that these clusters are physically associated. Clear evidence of mass segregation is seen. This study appears in this special issue devoted to the Chandra Carina Complex Project, a 1.42 deg{sup 2} Chandra X-ray survey of the Great Nebula in Carina.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

ARE LOW-LUMINOSITY GAMMA-RAY BURSTS GENERATED BY RELATIVISTIC JETS?

Low-luminosity gamma-ray bursts (ll-GRBs) constitute a subclass of GRBs that play a central role in the GRB-supernova connection. While ll-GRBs differ from typical long GRBs (LGRBs) in many aspects, they also share some common features. Therefore, the question whether the gamma-ray emission of ll-GRBs and LGRBs has a common origin is of great interest. Here we address this question by testing whether ll-GRBs, like LGRBs according to the Collapsar model, can be generated by relativistic jets that punch holes in the envelopes of their progenitor stars. The Collapsar model predicts that the durations of most observed bursts will be comparable to, or longer than, the time it takes the jets to break out of the star. We calculate the jet breakout times of ll-GRBs and compare them to the observed durations. We find that there is a significant excess of ll-GRBs with durations that are much shorter than the jet breakout time and that these are inconsistent with the Collapsar model. We conclude that the processes that dominate the gamma-ray emission of ll-GRBs and of LGRBs are most likely fundamentally different.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

Possibility of anisotropic curvature in cosmology

In addition to shear and vorticity a homogeneous background may also exhibit anisotropic curvature. Here a class of spacetimes is shown to exist where the anisotropy is solely of the latter type, and the shear-free condition is supported by a canonical, massless 2-form field. Such spacetimes possess a preferred direction in the sky and at the same time a CMB which is isotropic at the background level. A distortion of the luminosity distances is derived and used to test the model against the CMB and supernovae (using the Union catalog), and it is concluded that the latter exhibit a higher-than-expected dependence on angular position. It is shown that future surveys could detect a possible preferred direction by observing {approx}20/({Omega}{sub k0}{sup 2}) supernovae over the whole sky.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1970

Slide checkout console

Semiautomatic 35-mm photographic slide checkout console optically and electronically verifies registration of slides at a minimum rate of 250/hr. The console compares slide registration with a registration standard within the console. It verifies a binary code number on the bottom of the slide and visually displays its equivalent.

Nides, A. S.↗
NASA NTRS1980

IUE observations of long period eclipsing binaries - A study of accretion onto non-degenerate stars

IUE observations made in 1978-1979 recorded a whole class of interacting long-period binaries similar to beta Lyrae, which includes RX Cas, SX Cas, V 367 Cyg, W Cru, beta Lyr, and W Ser, called the W Serpentis stars. These mass-transferring binaries with relatively high mass transfer rate show two prominent features in the far ultraviolet: a continuum with a color temperature higher than the one observed in the optical region (about 12,000 K), and a strong emission line spectrum with the N V doublet at 1240 A, C IV doublet at 1550 A and lines of Si II, Si III, Si IV, C II, Fe III, AI III, etc. These phenomena are discussed on the assumption that they are due to accretion onto non-degenerate stars.

Plavec, M. J.↗
NASA NTRS1982

IUE studies of X-ray K-M dwarfs

X-ray and ultraviolet data are presented with various optical data. Certain flare star and BY Draconis type variable star data are included. The results are discussed in terms of parameters of interest such as rotation and binary incidence. Deviations from correlations of properties that are found in the literature are noted. The fairly sizable number of red dwarfs that were observed inhance the value of the set of data. The coronae and the chromospheres of transition regions of the nearby stars are also considered.

Johnson, H. M.↗
NASA NTRS1985

The 1982-1984 Eclipse of Epsilon Aurigae

A workshop proceedings concerned with the new data collected during the 1982-1984 eclipse period of the 27-year system Epsilon Aurigae is presented. This binary star has been a classic problem in astrophysics because the opaque eclipsing object is nonstellar, and probably disk shaped. Invited papers concerning the history of the system, optical, infrared and ultraviolet photometry, optical polarimetry and ultraviolet spectroscopy are included. An invited paper concerning comprehensive theoretical interpretation in the context of stellar evolution also is included. The information collected herein is unparalleled in scope and will remain a standard reference until the next eclipse cycle in the year 2009 A.D., in all probability.

Stencel, R. E.↗
NASA NTRS1987

Cataclysmic variables. Recent multi-frequency observations and theoretical developments; Proceedings of the 93rd IAU Colloquium, Bamberg, West Germany, June 16-19, 1986

Papers are presented on the formation and evolution of low-mass close binaries with compact components, the periods of cataclysmic variables, multiwavelength observations of dwarf novae during outbursts, and radio emission from cataclysmic variables. Also considered are long-term optical photometry of the dwarf nova VW Hyi, periodic modulations in the optical light curves of EX Hydrae, and Echelle-Mepsicron time-resolved spectroscopy of the dwarf nova SS Cygni. Other topics include UV and X-ray observations of cataclysmic variables, new EXOSAT observations of TV Columbae, accretion disk evolution, and the boundary layer in cataclysmic variables.

Drechsel, H.↗
NASA NTRS1992

Gamma-ray bursts as the death throes of massive binary stars

We propose that gamma-ray bursts are created in the mergers of double neutron star binaries and black hole neutron star binaries at cosmological distances. Two different processes provide the electromagnetic energy for the bursts: neutrino-antineutrino annihilation into electron-position pairs during the merger, and magnetic flares generated by the Parker instability in a postmerger differentially rotating disk. In both cases, an optically thick fireball of size less than or approximately equal to 100 km is initially created, which expands ultrarelativistically to large radii before radiating. The scenario is only qualitative at this time, but it eliminates many previous objections to the cosmological merger model. The strongest bursts should be found close to, but not at the centers of, galaxies at redshifts of order 0.1, and should be accompanied by bursts of gravitational radiation from the spiraling-in binary which could be detected by LIGO.

Narayan, Ramesh↗
NASA NTRS1995

Selected highlights from the Extreme Ultraviolet Explorer

We present a few scientific highlights from the Extreme Ultraviolet Explorer (EUVE) all-sky and deep surveys, from the EUVE Righ Angle Program, and from the EUVE Guest Observer Program. The First EUVE Source Catalog includes 410 extreme ultraviolet (EUV) sources detected in the initial processing of the EUVE all-sky data. A program of optical identification indicates that counterparts include cool star coronae, flare stars, hot white dwarfs, central stars of planetary nebulae, B star photospheres and winds, an X-ray binary, extragalactic objects (active galactic nuclei, BL Lacertae), solar system objects (Moon, Mars, Io,), supernova remnants, and two novae.

Bowyer, S.↗
NASA NTRS2017

Studying the Accretion Geometry of EXO 2030+375 at Luminosities Close to the Propeller Regime

The Be X-ray binary EXO2030+375 was in an extended low-luminosity state during most of 2016. We observed this state with NuSTAR and Swift, supported by INTEGRAL observations and optical spectroscopy with the Nordic Optical Telescope (NOT). We present a comprehensive spectral and timing analysis of these data here to study the accretion geometry and investigate a possible onset of the propeller e ect. The H data show that the circumstellar disk of the Be-star is still present. We measure equivalent widths similar to values found during more active phases in the past, indicating that the low-luminosity state is not simply triggered by a smaller Be disk. The NuSTAR data, taken at a 3-78 keV luminosity of 6:8 1035 erg s-1 (for a distance of 7.1 kpc), are nicely described by standard accreting pulsar models such as an absorbed power law with a high-energy cuto. We find that pulsations are still clearly visible at these luminosities, indicating that accretion is continuing despite the very low mass transfer rate. In phaseresolved spectroscopy we find a peculiar variation of the photon index from 1.5 to 2.5 over only about 3% of the rotational period. This variation is similar to that observed with XMM-Newton at much higher luminosities. It may be connected to the accretion column passing through our line of sight. With Swift/XRT we observe luminosities as low as 1034 erg s-1 where the data quality did not allow us to search for pulsations, but the spectrum is much softer and well described by either a blackbody or soft power-law continuum. This softer spectrum might be due to the accretion being stopped by the propeller e ect and we only observe the neutron star surface cooling.

Fürst, F.↗
DOE OSTI2010

THE BLACK HOLE MASS DISTRIBUTION IN THE GALAXY

We use dynamical mass measurements of 16 black holes in transient low-mass X-ray binaries to infer the stellar black hole mass distribution in the parent population. We find that the observations are best described by a narrow mass distribution at 7.8 {+-} 1.2 M{sub sun}. We identify a selection effect related to the choice of targets for optical follow-ups that results in a flux-limited sample. We demonstrate, however, that this selection effect does not introduce a bias in the observed distribution and cannot explain the absence of black holes in the 2-5 M{sub sun} mass range. On the high-mass end, we argue that the rapid decline in the inferred distribution may be the result of the particular evolutionary channel followed by low-mass X-ray binaries. This is consistent with the presence of high-mass black holes in the persistent, high-mass X-ray binary sources. If the paucity of low-mass black holes is caused by a sudden decrease of the supernova explosion energy with increasing progenitor mass, this would have observable implications for ongoing transient surveys that target core-collapse supernovae. Our results also have significant implications for the calculation of event rates from the coalescence of black hole binaries for gravitational wave detectors.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Light Curves and Spectra from a Unimodal Core-collapse Supernova

To assess the effectiveness of optical emission as a probe of spatial asymmetry in core-collapse supernovae (CCSNe), we apply in this paper the radiative transfer software SuperNu to a unimodal CCSN model. The SNSPH radiation hydrodynamics software was used to simulate an asymmetric explosion of a 16 ${M}_{\odot }$ zero-age main-sequence binary star. The ejecta has 3.36 ${M}_{\odot }$ with 0.024 ${M}_{\odot }$ of radioactive 56 Ni, with unipolar asymmetry along the z-axis. For 96 discrete angular views, we find a ratio between maximum and minimum peak total luminosities of ~1.36. The brightest light curves emerge from views orthogonal to the z-axis. Multigroup spectra from UV to IR are obtained. We find a shift in wavelength with viewing angle in a near-IR Ca ii emission feature, consistent with Ca being mostly in the unimode. We compare emission from the gray gamma-ray transfer in SuperNu and from the detailed gamma-ray transfer code Maverick. Relative to the optical light curves, the brightness of the gamma-ray emission is more monotonic with respect to viewing angle. UBVRI broadband light curves are also calculated. Parallel with the unimode, the U and B bands have excess luminosity at $\gtrsim 10$ days post-explosion, due to 56 Ni on the unimode. Finally, we compare our CCSN model with SN 2002ap, which is thought to have a similar ejecta morphology.

79 ASTRONOMY AND ASTROPHYSICS↗