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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 145 records · Page 8
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NASA NTRS1999

Black Hole X-Ray Nova Outburst with XTE and HST

We obtained multiwavelength coverage of the soft X-ray transient GRO J1655-40 during its 1996 outburst, using HST, RXTE, CGRO, and ground-based facilities. This outburst was qualitatively different from other SXT outbursts and from previous outbursts of this source. The onset of hard X-ray activity occurred very slowly, over several months, and was delayed relative to the soft X-ray rise. During this period, the optical fluxes declined steadily. This apparent anticorrelation is not consistent with with the standard disk instability model of SXT outbursts, nor is it expected if the optical output is dominated by reprocessed X-rays, as in persistent low-mass X-ray binaries. .

Patterson, Joseph↗
NASA NTRS1998

Black Hole X Ray Nova Outburst with XTE and HST

We obtained multiwavelength coverage of the soft X-ray transient. GRO J1655-40 during its 1996 outburst, using HST (Hubble Space Telescope), RXTE (Rossi X Ray Timing Explorer), CGRO (Compton Gamma Ray Observatory), and ground-based facilities. This outburst was qualitatively different from other SXT (Soft X Ray Telescope) outbursts and from previous outbursts of this source. The onset of hard X-ray activity occurred very slowly, over several months, and was delayed relative to the soft X-ray rise. During this period, the optical fluxes declined steadily. This apparent anticorrelation is not consistent with with the standard disk instability model of SXT outbursts, nor is it expected if the optical output is dominated by reprocessed X-rays, as in persistent low-mass X-ray binaries. Based on the strength of the 2175-A interstellar absorption feature, we constrain the reddening to be E(B - V) = 1.2 plus or minus 0.1, a result which is consistent with the known properties of the source and with the strength of other interstellar absorption lines. After this dereddening we find that the spectra are dominated by a component peaking in the optical, with the expected v (sup l/3) disk spectrum seen only in the ultraviolet. Bowen fluorescence lines of NIII and OIII are also seen, as well as possible P Cyg profiles in the ultraviolet resonance lines. These features suggest an accretion-disk wind. The X-ray spectra broadly resemble the high/soft state commonly seen in black hole candidates, but evolve through two substates.

Patterson, Joseph↗
NASA NTRS2000

HST Studies of the Chromospheres, Wind, and Mass-Loss Rates of Cool Giant and Supergiant Stars

UV spectra of K-M giant and supergiant stars and of carbon stars have been acquired with the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope (HST). These spectra have been used to measure chromospheric flow and turbulent velocities, study the acceleration of their stellar winds, acquire constraints on their outer atmospheric structure, and enable estimates of their mass-loss rates. Results from our observations of the giant stars Gamma Dra (K5 III hybrid), Alpha Tau (K5 III), Gamma Cru (M3.4 III), Mu Gem (M3 IIIab), and 30 Her (MG III), the supergiants Alpha Ori (M2 Iab) and Lambda Vel (K5 Ib), and the carbon stars TX Psc (NO; C6,2) and TW Hor (NO; C7,2) will be summarized and compared. The high resolution and wavelength accuracy of these data have allowed the direct measurement of the acceleration of the stellar winds in the chromospheres of several of these stars (from initial velocities of 3-9 km/s to upper velocities of 15-25 km/s) and of the chromospheric macroturbulence (-25-35 km/s). The high signal-to-noise and large dynamic range of these spectra have allowed the detection and identification of numerous new emission features, including weak C IV emission indicative of hot transition-region plasma in the non-coronal giant Alpha Tau, many new fluorescent lines of Fe II, and the first detection of fluorescent molecular hydrogen emission and of Ca II recombination lines in the UV spectrum of a giant star. The UV spectrum of two carbon stars have been studied with unprecedented resolution and reveal extraordinarily complicated Mg II lines nearly smothered by circumstellar absorptions. Finally, comparison of synthetic UV emission line profiles computed with the Lamers et al. (1987) Sobolev with Exact Integration (SEI) code with observations of chromospheric emission lines overlain with wind absorption features provides estimates of the mass-loss rates for four of these stars.

Carpenter, Kenneth G.↗
NASA NTRS2001

Fe(+) Emission from Eta Carinae B and D Blobs: Theory and HST Observations

We present comparisons between numerical simulations of Fe II emission spectra and HST high-resolution and signal-to-noise spectra of the Eta Carinae Weigelt B & D blobs. The spectra show a wealth of FeII and [FeII] lines. We investigate the dependence of the spectrum on electron density and on pumping by blackbody radiation. Using the photoionization code Cloudy we were able successfully reproduce the fluxes of few hundred FeII & [Fe II] lines in the range from 4000A to 6000A. Fe II emission analysis in Eta Car ejecta is very important because it provides information about excitation conditions, the electron temperature and density solved in a selfconsistent way. Moreover, for the first time we were able to use Fe II emission analysis itself to put limits on CNO abundances in emitting regions.

Verner, E.↗
NASA NTRS2002

Continuum Fitting HST QSO Spectra

The Principal Component Analysis (PCA) method which we are using to fit and describe QSO spectra relies upon the fact that QSO continuum are generally very smooth and simple except for emission and absorption lines. To see this we need high signal-to-noise (S/N) spectra of QSOs at low redshift which have relatively few absorption lines in the Lyman-a forest. We need a large number of such spectra to use as the basis set for the PCA analysis which will find the set of principal component spectra which describe the QSO family as a whole. We have found that too few HST spectra have the required S/N and hence we need to supplement them with ground based spectra of QSOs at higher redshift. We have many such spectra and we have been working to make them suitable for this analysis. We have concentrated on this topic since 12/15/01.

Tytler, David↗
NASA NTRS2002

HST NICMOS Observations of the Polarization of NGC 1068

We have observed the polarized light at 2 microns in the center of NGC 1068 with HST (Hubble Space Telescope) NICMOS (Near Infrared Camera Multi Object Spectrometer) Camera 2. The nucleus is dominated by a bright, unresolved source, polarized at a level of 6.0 +/- 1.2% with a position angle of 122 degrees +/- 1.5 degrees. There are two polarized lobes extending tip to 8" northeast and southwest of the nucleus. The polarized flux in both lobes is quite clumpy, with the maximum polarization occurring in the southwest lobe at a level of 17% when smoothed to 0.23" resolution. The perpendiculars to the polarization vectors in these two lobes point back to the intense unresolved nuclear source to within one 0.076" Camera 2 pixel, thereby confirming that this source is the origin of the scattered light and therefore the probable AGN (Active Galactic Nuclei) central engine. Whereas the polarization of the nucleus is probably caused by dichroic absorption, the polarization in the lobes is almost certainly caused by scattering, with very little contribution from dichroic absorption. Features in the polarized lobes include a gap at a distance of about 1" from the nucleus toward the southwest lobe and a "knot" of emission about 5" northwest of the nucleus. Both features had been discussed by groundbased observers, but they are much better defined with the high spatial resolution of NICMOS. The northeast knot may be the side of a molecular cloud that is facing the nucleus, which cloud may be preventing the expansion of the northeast radio lobe at the head of the radio synchrotron-radiation-emitting jet. We also report the presence of two ghosts in the Camera 2 polarizers.

Simpson, Janet P.↗
NASA NTRS2003

Thermal Vacuum Test Performance of the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) Variable Conductance Heat Pipe Assembly

The Variable Conductance Heat Pipe (VCHP) Assembly of the HST Wide Field Camera 3 was subjected to thermal vacuum (TN) environmental testing. The test program included both maximum and minimum environments as well as simulated on-orbit cycling. Elements of the VCHP assembly included a VCHP, an optical bench cold plate with an imbedded constant conductance heat pipe, and a VCHP reservoir radiator with a proportionally controlled heater. The purpose of the test was to characterize and demonstrate the assembly s ability to control the temperature of the cold plate, which provides a stable thermal environment for the instrument s optical bench. This paper discusses the VCHP Assembly control performance and control authority during the dynamic hot and cold 90-minute orbit cycling test phases.

Cleveland, Paul E.↗
NASA NTRS2004

Measuring the Mass Distribution in Z is Approximately 0.2 Cluster Lenses with XMM, HST and CFHT

Being the most massive gravitationally bound objects in the Universe, clusters of galaxies are prime targets for studies of structure formation and evolution. Specifically the comoving space density of virialized clusters of a given mass (or X-ray temperature), but also the frequency and degree of substructure, as well as the shape of the cluster mass profile are quantities whose current values and evolution as a function of lookback time can provide important constraints on the cosmological and physical parameters of structure formation theories. The project funded by NASA grant NAG 5-10041 intended to take such studies to a new level by combining observations of a well-selected cluster sample by three state-of-the-art telescopes: HST, to accurately measure the mass distribution in the cluster core (approx. 0.5 h(sup -1)(sub 50) Mpc) via strong gravitational lensing; CFHT, to measure the large scale mass distribution out to approx. 3 Mpc via weak lensing; and XMM, to measure the gas density and temperature distribution accurately on intermediate scales < 1.5 Mpc. XMM plays a pivotal role in this context as the calibration of X-ray mass measurements through accurate, spatially resolved X-ray temperature measurements (particularly in the cosmologically most sensitive range of kT> 5 keV) is central to the questions outlined above. This set of observations promised to yield the best cluster mass measurements obtained so far for a representative sample, thus allowing us to: 1) Measure the high-mass end of the local cluster mass function; 2) Test predictions of a universal cluster mass profile; 3) calibrate the mass-temperature and temperature-luminosity relations for clusters and the scatter around these relations, which is vital for studies of cluster evolution using the X-ray temperature and X-ray luminosity functions.

Source record↗
NASA NTRS2000

Intensive HST, RXTE, and ASCA Monitoring of NGC 3516: Evidence against Thermal Reprocessing

During 1998 April 1316, the bright, strongly variable Seyfert 1 galaxy NGC 3516 was monitored almost continuously with HST for 10.3 hr at ultraviolet wavelengths and 2.8 days at optical wavelengths, and simultaneous RXTE and ASCA monitoring covered the same period. The X-ray fluxes were strongly variable with the soft (0.5-2 keV) X-rays showing stronger variations (approx. 65% peak to peak) than the hard (2-10 keV) X-rays (approx. 50% peak to peak). The optical continuum showed much smaller but still highly significant variations: a slow approx. 2.5% rise followed by a faster approx. 3.5% decline. The short ultraviolet observation did not show significant variability. The soft and hard X-ray light curves were strongly correlated, with no evidence for a significant interband lag. Likewise, the optical continuum bands (3590 and 5510 A) were also strongly correlated, with no measurable lag, to 3(sigma) limits of approx. less than 0.15 day. However, the optical and X-ray light curves showed very different behavior, and no significant correlation or simple relationship could be found. These results appear difficult to reconcile with previous reports of correlations between X-ray and optical variations and of measurable lags within the optical band for some other Seyfert 1 galaxies. These results also present serious problems for "reprocessing" models in which the X-ray source heats a stratified accretion disk, which then reemits in the optical/ultraviolet : the synchronous variations within the optical would suggest that the emitting region is approx. less than 0.3 It-day across, while the lack of correlation between X-ray and optical variations would indicate, in the context of this model, that any reprocessing region must be approx. greater than 1 It-day in size. It may be possible to resolve this conflict by invoking anisotropic emission or special geometry, but the most natural explanation appears to be that the bulk of the optical luminosity is generated by some mechanism other than reprocessing.

Edelson, Rick↗
NASA NTRS2004

Monitoring the Variable Absorption in the Seyfert 1 Galaxy NGC 3783 with FUSE, HST, and Chandra Observations

The analysis of FUSE observations funded by this grant aims to understand the nature and origin of the absorbing gas in NGC 3783. We have used the simultaneous FUSE, HST, and Chandra data to determine the radial location, density, and ionization state of the absorbing gas and measure its evolution in ionization, column density, velocity, and coverage of the active nucleus. As part of this program, Dr. Gerard Kriss supplied advice and assistance in planning and scheduling the FUSE observations of NGC 3783 coordinated with the HST/STIS observations, and co-authored the publications listed in the bibliography and summarized below.

Kriss, Gerard A.↗
NASA NTRS2004

A Complex Two Dimensional Spectroscopic Database: The HST Treasury Archive for Eta Carinae

The HST Treasury Program on eta Carinae produced one of the most complex and ambitious spectroscopic datasets obtained with the Hubble Space Telescope. The archival database includes the STIS/CCD and MAMA data during its recent spectroscopic event in 2003, plus all of the STIS observations of the object and its ejecta obtained during its spectroscopic cycle beginning in 1998. The database permits users to query via instrument, target, date, wavelength range, position angle, and position and allows the user to display the spectrum and download it in fits format. We have also developed software for ease of extraction and display and analysis. The user can go from an initial query to doing science in only 20 minutes! A demonstration of the database and software will be available at the poster.

Humphreys, R. M.↗
NASA NTRS1995

HST Observations of the Luminous IRAS Source FSC10214+4724: A gravitationally Lensed Infrared Quasar

Observations of a distant object in space with the data being taken by the Hubble Space Telescope (HST) Wide Field Planetary Camera. Scientific examination and hypothesis related to this object which appears to be either an extremely luminous dust embedded quasar, or a representative of a new class of astronomical objects (a primeval galaxy).

Hubble Space Telescope Quasar Space Object Astrono↗
NASA NTRS1998

The HST Key Project on the Extragalactic Distance Scale

We report the detection of Cepheids and a new distance to the spiral galaxy NGC 2541, based on data obtained with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope (HST).

Cepheids spiral galaxy Hubble Space Telescope Extr↗