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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Evolution of wide binary millisecond pulsars in globular clusters

The evolution of a binary radio pulsar in a wide orbit about a low-mass degenerate dwarf companion in a globular cluster environment is investigated. An extensive series of numerical scattering experiments is used to study encounters between such a pulsar and passing cluster field stars. A wide range of initial orbital periods from 3 to 1000 days is considered with a corresponding range of masses for the degenerate dwarf companions. The calculative results are summarized in the form of scattering cross sections. In particular, cross sections are presented for three final 'channels' in which the end product of the encounter is an isolated neutron star. Cross sections for inducing various orbital eccentricities into initially circular orbits are also derived. The implications of the results for the formation of the single millisecond pulsars in M28 and M15 and for the nearly circular obit of the M4 binary radio pulsar are discussed.

Rappaport, S.↗
NASA NTRS1990

A classification of the galaxy groups

A statistical criterion has been proposed to reveal the random and physical clusterings among stars, galaxies and other objects. This criterion has been applied to the galaxy triples of the list by Karachentseva, Karaschentsev and Scherbanovsky, and the double galaxies of the list by Dahari where the primary components are the Seyfert galaxies. The confident physical, probable physical, probable optical and confident optical groups have been identified. The limit difference of radial velocities of components for the confident physical multiple galaxies has also been estimated.

Anosova, Joanna P.↗
NASA NTRS1991

Hubble Space Telescope: A cosmic time machine

The mission of the Hubble Space Telescope (HST) is to explore the expanding and evolving universe. During the 3,000 operating hours every year for the next 15 years or more, the HST will be used to study: galaxies; pulsars; globular clusters; neighboring stars where planets may be forming; binary star systems; condensing gas clouds and their chemical composition; and the rings of Saturn and the swirling ultraviolet clouds of Venus. The major technical achievements - its nearly perfect mirrors, its precise guidance system of rate gyroscopes, reaction wheels, star trackers, and fine guidance sensors are briefly discussed. The scientific instruments on board HST are briefly described. The integration of the equipment and instruments is outlined. The Space Telescope Science Institute (STScI) has approved time for 162 observations from among 556 proposals. The mission operation and data flow are explained.

Westphal, J. A.↗
NASA NTRS1991

Luminous clusters of Wolf-Rayet stars in the SBmIII galaxy NGC 4214

Observations are reported of strong broad emission lines attributed to WR stars in the spectra of several bright knots in the nearby Magellanic irregular galaxy NGC 4214 (classified as type SBmIII), in addition to the emission produced by the more prevalent WN stars). Data are presented on measurements of the line fluxes, the line equivalent widths, and continuum flux densities in the four observed knots, showing that the strongest WR lines generally appear in knots having the most luminous stellar continuum. The significance of this observation is discussed.

Sargent, Wallace L. W.↗
NASA NTRS1992

The Galactic center wind

The combined effect of winds from a cluster of stars in the central 0.8 pc of the Galaxy is modeled as uniform power and mass input over the central region. The flow becomes supersonic outside the central region, and the expected decrease in pressure is in approximate accord with observations. The pressure variations on a larger scale suggest that the Galactic center wind passes through a shock front at a radius of a few pc, leading to a shocked wind bubble on a scale of 100 pc. The tangential magnetic field can come to dominate the pressure in the shocked wind flow even if the energy density of the magnetic field in the initial wind is only 0.1 percent of the wind kinetic energy density. The magnetic region produced in this way may be related to some of the apparently magnetized structures observed in the central region of the Galaxy.

Chevalier, Roger A.↗
NASA NTRS1992

Hubble Space Telescope Planetary Camera images of R136

Images obtained with the Planetary Camera on the HST is used here to study the stellar population of R136, the core of the 30 Doradus cluster. It is found that R136a, the brightest knot at the center of R136, is indeed a tight cluster of stars containing at least 12 components in a 1 arcsec region. Three of the stars are of the Wolf-Rayet (W-R) type. The brightest stars have luminosities consistent with their being massive O supergiants or W-R stars. The stellar mass density in R136a is at least a million tiems that of the solar neighborhood. In the larger region known as R136, the magnitudes of 214 stars are detected and measured. A color-magnitude diagram shows a range of stars from luminous O supergiants to ZAMS B3 stars. The diagram is very similar to that of stars outside of R136. A surface brightness profile constructed from stellar photometry is best fit by a pure power law.

Campbell, Bel↗
NASA NTRS1992

Ultraviolet observations of clusters of Wolf-Rayet stars in the SBm3 galaxy NGC 4214 and Ultraviolet and optical observations of LINER's

The purpose of the grant was to obtain and analyze IUE (UV) and ground-based (optical) spectra of the central bar of NGC 4214, which contains several bright H II regions, in order to further explore the properties of the Wolf-Rayet stars in this galaxy. Several spatially distinct regions, with widely different equivalent widths of optical Wolf-Rayet lines, could be sampled by the large IUE entrance aperture. By using newly developed extraction techniques, the spectra of these H II regions could be isolated, and differences in their stellar populations would be systematically studied. Data were obtained with IUE in late February and early March, 1992. Some of the shifts were successful, but a few were not -- apparently the blind offset from the nearby star did not work equally well in all cases. Thus, the signal-to-noise ratio is somewhat lower than we had hoped. This necessitated a more careful extraction of the spectra of individual H II regions from the two-dimensional spectra. (A program that models the point spread function in the spatial direction was used to deblend the distinct H II regions.) The IUE data are currently being analyzed in conjunction with ground-based optical spectra. There appear to be obvious variations in the stellar population over angular scales of only a few arc seconds. The second part of the research performed under this grant was a continuation of a project that uses IUE (UV) and ground-based (optical) spectra to infer the physical conditions in Low-Ionization Nuclear Emission-Line Regions (LINER's). We have obtained spectra of a few key objects that cover a representative range in LINER continuum and emission-line properties. The overall goals are to (1) separate the emission into spatially distinct components, (2) establish whether the observed nuclear ultraviolet continua indicate sufficient photoionizing fluxes to account for the emission lines, (3) determine whether the nuclear emission can be explained by hot stars alone, (4) detect and measure the strengths of UV emission lines, and (5) search for systematic differences in the UV spectra of LINER's whose other properties differ in some respects.

Filippenko, Alexei V.↗
NASA NTRS1994

The structure and nature of NGC 2017 IRS. 1: High-resolution radio continuum maps

We have observed the star formation cluster NGC 2071 IRS 1, 2, and 3, with 0.14 sec spatial resolution at 2 cm. The strong source IRS 1 breaks up into a bright peak sitting on a narrow line emission extending over about 400 AU, with three much weaker peaks. This ridge, which has a p.a. = 100 deg, is not aligned with any of the other structures that have previously been seen around IRS 1: its orientation is about 55 deg from the CO outflow direction, and 35 deg from a hypothetical disk direction. The spectral and spatial results, combined with earlier radio and infrared observations, indicate that most likely the radio and infrared emission from the exciting source, IRS 1, is produced by a dense wind hidden by at least 100 visual magnitudes of extinction; the extended ridge of emission comes from an optically thin H II region with characteristic dimensions of approximately AU and which may result from a clumpy distribution of local gas and dust.

Smith, Howard A.↗
NASA NTRS1994

Comparative pulsation calculations with OP and OPAL opacities

Comparative linear nonadiabatic pulsation calculations are presented using the OPAL and Opacity Project opacities. The two sets of opacities include effects due to intermediate coupling and fine structure as well as new abundances. We used two mass luminosity (M-L) relations, one standard (BIT), and one employing substantial convective core overshoot (COV). The two sets of opacities cannot be differentiated on the basis of the stellar pulsation calculations presented here. The BIT relation can model the beat and bump Cepheids with masses between 4 and 7 solar mass, while if the overshoot relation is used, masses between 2 and 6 solar mass are required. In the RR Lyrae regime, we find the inferred masses of globular cluster RRd stars to be little influenced by the choice of OPAL or OP. Finally, the limited modeling we have done is not able to constrain the Cepheid M-L relation based upon period ratios observed in the beat and bump stars.

Kanbur, Shashi M.↗
NASA NTRS2000

Outflows, Jets and Shocks in the Orion Nebula

The rich young cluster of stars associated with the Orion Nebula provides a unique laboratory for the study of plasma phenomena. We see five types of flows and shocks. Photoablation outflow from the proplyds nearest theta (exp 1) Ori C form nearly stationary shocks with the high velocity wind from that star. Microjets, with scales of less than 10 (exp 4) AU, are seen around some 20 low mass stars. Isolated jets, with high velocities and scales of about, 104 AU, are less numerous but common. One also sees the shocks formed when these jets impinge on the ionized nebular gas and the neutral gas in the foreground lid. The final type of object is the stationary shock formed by the interaction from the stellar wind that arises during disk formation with the ambient, gas flowing away from the main body of the nebula.

ODell, C. R.↗
NASA NTRS2006

The Hard X-ray 20-40 keV AGN Luminosity Function

We have compiled a complete, significance limited extragalactic sample based on approximately 25,000 deg(sup 2) to a limiting flux of 3 x 10(exp -11) ergs per square centimeter per second. (approximately 7,000 deg(sup 2)) to a flux limit of 10(exp -11) ergs per square centimeter per second)) in the 20 - 40 keV band with INTEGRAL. We have constructed a detailed exposure map to compensate for effects of non-uniform exposure. The flux-number relation is best described by a power-law with a slope of alpha = 1.66 plus or minus 0.11. The integration of the cumulative flux per unit area leads to f(sub 20-40 keV) = 2.6 x 10(exp -10) ergs per square centimeter per second per sr(sup -1) which is about 1% of the known 20-40 keV X-ray background. We present the first luminosity function of AGN in the 20-40 keV energy range, based on 68 extragalactic objects detected by the imager IBIS/ISGRI on-board INTEGRAL. The luminosity function shows a smoothly connected two power-law form, with an index of gamma (sub 1) = 0.9 below, and gamma (sub 2) = 2.2 above the turn-over luminosity of L(sub *), = 4.6 x 10(sup 43) ergs per second. The emissivity of all INTEGRAL AGNs per unit volume is W(sub 20-40keV)(greater than 10(sup 41) ergs per second) = 2.8 x 10(sup 38) ergs per second h(sup 3)(sub 70) Mpc(sup -3). These results are consistent with those derived in the 2-20keV energy band and do not show a significant contribution by Compton-thick objects. Because the sample used in this study is truly local (z(raised bar) = 0.022)), only limited conclusions can be drawn for the evolution of AGNs in this energy band. But the objects explaining the peak in the cosmic X-ray background are likely to be either low luminosity AGN (L(sub x) less than 10(sup 41) ergs per second) or of other type, such as intermediate mass black holes, clusters, and star forming regions.

Beckmann, V.↗
NASA NTRS1997

HST/WFPC2 Observations of Warm Ultraluminous Infrared Galaxies

We present new high resolution B- ad I--band images of a nearly complete sample of 9 warm (f(sub 25)/f(sub 60) > 0.2) ultraluminous galaxies (ULIGs) obtained with the Wide Field Planetary Camera (WFPC2) of the Hubble Space Telescope (HST).

infrared star clusters interactions active starbur↗
NASA NTRS2007

GRB070125: The First Long-Duration Gamma-Ray Burst in a Halo Environment

We present the discovery and high signal-to-noise spectroscopic observations of the optical afterglow of the long-duration gamma-ray burst GRB070125. Unlike all previously observed long-duration afterglows in the redshift range 0.5 < z < 2.0, we find no strong (rest-frame equivalent width W > 1.0 A) absorption features in the wavelength range 4000 - 10000 A. The sole significant feature is a weak doublet we identify as Mg 11 2796 (W = 0.18 +/- 0.02 A), 2803 (W = 0.08 +0I.-01 ) at z = 1.5477 +/- 0.0001. The low observed Mg II and inferred H I column densities are typically observed in galactic halos, far away from the bulk of massive star formation. Deep ground-based imaging reveals no host directly underneath the afterglow to a limit of R > 25.4 mag. Either of the two nearest blue galaxies could host GRB070125; the large offset (d >= 27 kpc) would naturally explain the low column density. To remain consistent with the large local (i.e. parsec scale) circum-burst density inferred from broadband afterglow observations, we speculate GRB070125 may have occurred far away from the disk of its host in a compact star-forming cluster. Such distant stellar clusters, typically formed by dynamical galaxy interactions, have been observed in the nearby universe, and should be more prevalent at z>l where galaxy mergers occur more frequently.

Bradley, Cenko S.↗
NASA NTRS2010

Herschel-ATLAS: The Angular Correlation Function of Submillimetre Galaxies at High and Low Redshift

We present measurements of the angular correlation function of galaxies selected from the first field of the H-ATLAS survey. Careful removal of the background from galactic cirrus is essential, and currently dominates the uncertainty in our measurements. For our 250 micrometer-selected sample we detect no significant clustering, consistent with the expectation that the 250 pm-selected sources are mostly normal galaxies at z < or equal to 1. For our 350 micrometer and 500 micrometer-selected samples we detect relatively strong clustering with correlation amplitudes A of 0.2 and 1.2 at 1', but with relatively large uncertainties. For samples which preferentially select high redshift galaxies at z approx. 2-3 we detect significant strong clustering, leading to an estimate of r(0) approx. 7-11/h Mpc. The slope of our clustering measurements is very steep. delta approx. 2. The measurements are consistent with the idea that sub-mm sources consist of a low redshift population of normal galaxies and a high redshift population of highly clustered star-bursting galaxies.

Maddox, S. J.↗
NASA NTRS1994

Spectroscopy of the young cluster Blanco 1

We present spectroscopic observations of some 115 stars of the cluster Blanco 1, extending from the Ca II(H,K) region to the Ca II(I-R) triplet, supporting an age similar to that of the young cluster alpha Persei. The H-alpha absorption equivalent with vs (B - V) diagram forms a well-defined locus, with decreasing absorption equivalent width for decreasing effective temperature, akin to solar neighborhood dwarfs. A large spread in the Ca II surface flux, as a function of (B - V), also indicates the presence of a high degree of surface inhomogeneity, synonymous with high magnetic activity in young stars. A drop-off in the Ca II flux at (B - V) = 1.0 is also similar to the solar neighborhood stars, and shows that the primary chromospheric cooling changes from the Ca II and Mg II lines to the Balmer lines. The mean chromospheric temperature for stars at 4800 K lies between 8000 K and 10,000 K, based on theoretical models, which is somewhat higher than the older solar neighborhood dwarfs. The high mean Ca II surface flux of the sample is also consistent with that of other young clusters. We were able to measure the equivalent width of the Li(6708) line, whose strength as a function of (B - V) indicates an age similar to the young cluster alpha Persei. The lithium abundance decreases with decreasing effective temperature, consistent with the premise of lithium depletion in stars with larger convection zones. Using published photometry and a recent Zero Age Main Sequence (ZAMS) fitting method, we also re-define the distance to the cluster to be 246 pc.

Panagi, P. M.↗
NASA NTRS1987

Numerical models of star formation in X-ray cluster cooling flows

A grid of numerical models is used here to study how accretion flows are affected by star formation. The observables associated with these models are investigated, presenting their X-ray surface brightness profiles. An X-ray diagnostic is searched for that, in the absence of spatially resolved X-ray spectral data, can be an unambiguous indicator for ongoing star formation in cooling flows. The spatial distributions of newly formed stars are presented and compared to profiles of the accreting galaxy in each model. Whether the accretion population can form the luminous parts of the accreting galaxy or whether it forms a dark component is considered.

White, Raymond E., III↗
DOE OSTI2022

The Factory and the Beehive. IV. A Comprehensive Study of the Rotation X-Ray Activity Relation in Praesepe and the Hyades

X-ray observations of low-mass stars in open clusters are critical to understanding the dependence of magnetic activity on stellar properties and their evolution. Praesepe and the Hyades, two of the nearest, most-studied open clusters, are among the best available laboratories for examining the dependence of magnetic activity on rotation for stars with masses ≲1 M ⊙ . We present an updated study of the rotation–X-ray activity relation in the two clusters. We updated membership catalogs that combine pre-Gaia catalogs with new catalogs based on Gaia Data Release 2. The resulting catalogs are the most inclusive ones for both clusters: 1739 Praesepe and 1315 Hyades stars. We collected X-ray detections for cluster members, for which we analyzed, re-analyzed, or collated data from ROSAT, the Chandra X-ray Observatory, the Neil Gehrels Swift Observatory, and XMM-Newton. We have detections for 326 Praesepe and 462 Hyades members, of which 273 and 164, respectively, have rotation periods—an increase of 6× relative to what was previously available. We find that at ≈700 Myr, only M dwarfs remain saturated in X-rays, with only tentative evidence for supersaturation. We also find a tight relation between the Rossby number and fractional X-ray luminosity L X /L bol in unsaturated single members, suggesting a power-law index between –3.2 and –3.9. Lastly, we find no difference in the coronal parameters between binary and single members. These results provide essential insight into the relative efficiency of magnetic heating of the stars' atmospheres, thereby informing the development of robust age-rotation-activity relations.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2005

Proceedings of Protostars and Planets V

Oral presentation sessions in this conference include: Clouds and cores; Star formation and protostars; Binaries and multiples; Newborn massive stars; jets and outflows; Clusters and associations; T Tauri stars and disks; Brown dwarfs; Planet formation and evolution; Extrasolar planets; Dust and protoplanetary disks; Early solar system and Astrobiology. Poster presentations included: Clouds and Cores. Collapse and Protostars, Binaries and Multiples, Clusters, Associations, and the IMF, Jets and Outflows, T Tauri Stars and Other Young Stars, Disks and Disk Accretion, Brown Dwarfs, Herbig Ae/Be Stars and Massive Stars, Solar System Objects, Planet Formation, Extrasolar Planets and Planet Detection, Properties of Protoplanetary Disks, Migration and Planetary Orbits and Meteoritics and Astrobiology

Source record↗