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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Spectrophotometry of the transient X-ray source A0620-00

Optical observations of the transient X-ray source A0620-00 over the wavelength range from about 3200 to 6600 A are analyzed which were made with the 5-m Hale telescope using a multichannel spectrometer, a digital spectrograph with a cooled integrating SIT vidicon, and an image photon-counting system attached to the camera of the coude spectrograph. Infrared observations at 1.65, 2.2, and 3.5 microns are also examined. Individual spectral lines of special interest are discussed, the E(B-V) color excess is estimated to be about 0.40, and a distance of 1200 pc is adopted. Analysis of the continuous spectrum yields several simple binary models. A specific model is proposed in which one of the continuum sources is an optically thick object characterized by a model atmosphere at a temperature of 25,000 to 30,000 K and the second source is either a cool black body at 4000 K or a partially optically thick source of bound-free plus free-free radiation from a hydrogen gas with an electron temperature of at least 100,000 K. Some possible parameters of these sources and of the accretion disk are considered.

Oke, J. B.↗
NASA NTRS1983

High spatial resolution VLA observations of the R Aquarii jet

The Very Large Array was used to observe the jet feature of the symbiotic variable R Aquarii. A steady emission at 6 cm was confirmed for the past year, with the jet located 6.4 arcsec from R Aquarii at 29.3 deg PA. A velocity for the jet has been calculated as 40 km/sec, and may be accompanied by an ejection velocity in the range of 760-1800 km/sec. Since R Aquarii is the closest known object with a jet, further monitoring is recommended in order to detect any episodic mass transfer in what may be a binary system. The mass transfer, monitored at various wavelengths, would account for the observed optical and radio properties.

Kafatos, M.↗
NASA NTRS1994

ROSAT observations of the x ray binary HD 154791

We have been surveying the Taurus dark cloud for young stars using a variety of techniques. Two optical proper motion surveys identified 8 new pre-main sequence stars; an IRAS-based program discovered 6 new embedded sources and 4-6 new T Tauri stars. Finally, an optical objective prism survey found 12 new T Tauri stars. Our goal in this project is to examine and compare star formation in the dark clouds: Heiles cloud 2 (HCL2), L1537, L1538, and L1544. HCL2 is a very dense region actively forming young stars and contains 5-6 very young, deeply embedded sources; L1537 and L1538 have no known pre-main sequence stars; L1544 contains 7 optically visible T Tauri stars. These clouds appear roughly similar on optical sky survey plates. We would like to know why some of the clouds are active and why some are not. The first goal of the project is to survey the regions using IR photometry to identify very red pre-main sequence stars and X-ray imaging to identify solar-type young stars missed in the near-IR survey. We will follow up these observations with molecular line surveys to compare the conditions in various clouds with their star formation efficiencies.

Kenyon, Scott J.↗
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 NTRS1999

Hard X-Ray Emission of X-Ray Bursters

The primary goal of this proposal was to perform an accurate measurement of the broadband x-ray spectrum of a neutron-star low-mass x-ray binary found in a hard x-ray state. This goal was accomplished using data obtained under another proposal, which has provided exciting new information on the hard x-ray emission of neutron-star low-mass x-ray binaries. In "BeppoSAX Observations of the Atoll X-Ray Binary 4U0614+091", we present our analysis of the spectrum of 4U0614+091 over the energy band from 0.3-150 keV. Our data confirm the presence of a hard x-ray tail that can be modeled as thermal Comptonization of low-energy photons on electrons having a very high temperature, greater than 220 keV, or as a non-thermal powerlaw. Such a very hard x-ray spectrum has not been previously seen from neutron-star low-mass x-ray binaries. We also detected a spectral feature that can be interpreted as reprocessing, via Compton reflection, of the direct emission by an optically-thick disk and found a correlation between the photon index of the power-law tail and the fraction of radiation reflected which is similar to the correlation found for black hole candidate x-ray binaries and Seyfert galaxies. A secondary goal was to measure the timing properties of the x-ray emission from neutronstar low-mass x-ray binaries in their low/hard states.

Kaaret, P.↗
NASA NTRS2002

Kronos: A Multiwavelength Observatory for Mapping Accretion-Driven Sources

Kronos is a multiwavelength observatory proposed as a NASA Medium Explorer. Kronos is designed to make use of the natural variability of accreting sources to create microarcsecond-resolution maps of the environments of supermassive black holes in active galaxies and stella-size black holes in binary systems and to characterize accretion processes in Galactic compact binaries. Kronos will obtain broad energy range spectroscopic data with co-aligned X-ray, ultraviolet, and optical spectrometers. The high-Earth orbit of Kronos enables well-sampled, high time-resolution observations, critical for the innovative and sophisticated methods that are used to understand the accretion flows, mass outflows, jets, and other phenomena found in accreting sources. By utilizing reverberation mapping analysis techniques, Kronos produces advanced high-resolution maps of unprecedented resolution of the extreme environment in the inner cores of active galaxies. Similarly, Doppler tomography and eclipse mapping techniques characterize and map Galactic binary systems, revealing the details of the physics of accretion processes in black hole, neutron star, and white dwarf binary systems. The Kronos instrument complement, sensitivity, and orbital environment make it suitable to aggressively address time variable phenomena in a wide range of astronomical objects from nearby flare stars to distant galaxies.

Peterson, Bradley M.↗
NASA NTRS2018

Orbital Characterization of GJ1108A System, and Comparison of Dynamical Mass with Model-Derived Mass for Resolved Binaries

We report an orbital characterization of GJ1108Aab that is a low-mass binary system in the pre-main-sequence phase. Via the combination of astrometry using adaptive optics and radial velocity measurements, an eccentric orbital solution of e = 0.63 is obtained, which might be induced by the Kozai–Lidov mechanism with a widely separated GJ1108B system. Combined with several observed properties, we confirm that the system is indeed young. Columba is the most probable moving group, to which the GJ1108A system belongs, although its membership to the group has not been established. If the age of Columba is assumed for GJ1108A, the dynamical masses of both GJ1108Aa and GJ1108Ab (M(sub dynamical,GJ1108Aa) = 0.72 ± 0.04 Solar Mass and M(sub dynamical,GJ1108Ab) = 0.30 ± 0.03 Solar Mass) are more massive than what an evolutionary model predicts based on the age and luminosities. We consider that the discrepancy in mass comparison can be attributed to an age uncertainty; the system is likely older than stars in Columba, and effects that are not implemented in classical models such as accretion history and magnetic activity are not preferred to explain the mass discrepancy. We also discuss the performance of the evolutionary model by compiling similar low-mass objects in the evolutionary state based on the literature. Consequently, it is suggested that the current model on average reproduces the mass of resolved low-mass binaries without any significant offsets.

Mizuki, T.↗
NASA NTRS2017

Synergies of Subaru and CGI

Given the limited observing time and demanding scenarios of the WFIRST coronagraph instrument (CGI), it is critical to consider how Subaru observations can benefit its observing program. Subaru telescope has a suite of instruments with their adaptive optics (AO) and extreme adaptive optics modules (SCExAO). With SCExAO, the Subaru telescope is capable of detection and spectral characterization of binaries and bright (greater than 5(exp -6) contrast) companions in the near-infrared. This will enable the vetting of targets, disk detection and characterization, and potentially some additional science should CGI identify interesting targets during its technology demonstration and potential guest observer program. Additionally, large companions that are within the inner working angle of the coronagraph can be identified using the VAMPIRES aperture masking interferometer. With highly complementary target brightness and significantly overlapping fields of view, there is a great deal of potential for combined observations with Subaru and CGI. This will represent the first time single observations spanning the visible to near-infrared will be possible for high contrast imaging. We will discuss the overlap of instrumentation over time, the implication of instrument evolution as TMT comes online, and how this can be used to improve both science and technology demonstrations for CGI.

adaptive optics (AO↗
NASA NTRS1977

OSO-8 X-ray observations of AM Herculis

Hard X-ray observations of the binary system AM Her were coincident with soft X-ray and ground-based optical measurements. In the 2-60 KeV band, variability was detected with an eclipse during phases 0.5 to 0.7 with respect to the 0. d 12892 period optical minima, synchronous with the known soft X-ray eclipse. The 2-60 KeV uneclipsed flux was 9.5 x 10 to the minus 10th power erg sq cm/sec, of which 86% lies above 10 keV. Thus AM Her contains a hard source located near the similarly eclipsed soft X-ray source. The X-ray data are interpreted in terms of thermal bremsstrahlung from accretion onto a white dwarf.

Swank, J. H.↗
NASA NTRS1980

Simultaneous X-ray and optical observations of rapid variability in Scorpius X-1

Copernicus and SAS-3 observations of Sco X-1 during very active states show strong and rapid X-ray flickering with time scales as short as 20 sec. Simultaneous optical photometry reveals similar and remarkably well correlated flickering of lower amplitude. The level of correlation decreases when the X-ray source becomes fainter, but optical and X-ray fluxes, averaged over 1 min, are usually well correlated for B magnitudes less than 12.9. Cross-correlation analysis of the data during periods of high activity shows no really significant time delay between X-ray and optical features, although the cross-correlation function peaks systematically for positive lag values (optical following X-rays). The amplitude of the X-ray flickering exhibits a strong energy-dependence consistent with the well-known intensity versus spectral-hardness relation derived from previous observations. The highly correlated optical activity is interpreted as due to reprocessing of X-ray photons in the binary system.

Ilovaisky, S. A.↗
NASA NTRS1979

Soft X-ray observations of degenerate dwarfs and cataclysmic variables

Observations in outburst of two dwarf novae, SS Cyg and U Gem, reveal soft, pulsed X-ray emission greatly enhanced over the emission present during the quiescent periods. In order to characterize the nature of the X-ray pulsations a random phase analysis was carried out, which indicated the phase of SS Cyg behaved like a random variable with zero mean and an r.m.s. value that increased with the square root of the time. Attention is also given to the properties of the detected dwarf novae during optical quiescences, to isolated white dwarfs, and to optical observations of AM Her. It is concluded that the dwarf novae, which occur in binary systems, appear to be controlled by the varying accretion of matter generated by the main sequence companion, and that the X-ray emission during outburst appears to consist of two separate components: a periodically varying (on about a 10 s timescale) soft component, together with a more slowly randomly varying hard component.

Garmire, G.↗
NASA NTRS1980

The optical identification of H2252-035 with a cataclysmic variable

An improved position is presented for the X-ray source H2252-033 using the Ariel V Sky Survey Instrument, and precise positioning using the Scanning Modulation Collimator on HEAO-1. The source is identified optically with a 13th magnitude emission-line object, which is probably a white dwarf binary with a well formed accretion disk, with similarities to the dwarf novae (e.g., SS Cyg) at minimum.

Griffiths, R. E.↗
NASA NTRS1985

Low-mass X-ray binaries

A review is given of current understanding of low-mass X-ray binaries (LMXBs), which are luminous X-ray sources composed of a late-type optical companion (mass less than about 1 solar mass) and a neutron star (or possibly a black hole). Thirty-two LMXBs have been identified with optical counterparts in the Galaxy and one in the Large Magellanic Cloud (Brad and McClintock, 1983). It is unlikely that there are more than about 100 active LMXBs in the Galaxy, compared with about 200,000 cataclysmic variables. Topics covered in the review are: typical X-ray and optical properties; orbital periods; the nature of the compact source; accretion disks; formation; mass transfer mechanisms; and globular clusters and bright bulge X-ray sources.

Mcclintock, J. E.↗
NASA NTRS1989

The orbital inclination of Cygnus XR-1 measured polarimetrically

The X-ray binary Cyg XR-1/HDE 226868 was observed polarimetrically over one orbit at three different optical wavelengths. The standard theory of Brown, et al. (1978) is used to derive an orbital inclination i = 62 deg (+5 deg, -37 deg), where the error is the 90-percent-confidence interval derived by the method of Simmons, et al. (1980). The value of the orbital inclination is significantly lower than values based on polarimetric observations. The difference is a result of the observational protocols used. A bias toward larger values of the inclination caused by the tidal distortion of the primary is still found in the present result. The inclination derived corresponds to a mass of the compact component of 6.3 solar masses, above the maximum mass of any degenerate configuration consistent with general relativity except a black hole.

Dolan, Joseph F.↗
NASA NTRS1990

The spectra of relativistic accretion disks - Application to A0620-00

The X-ray flux emitted from a geometrically thin, relativistic accretion disk in the steady state approximation is investigated in order to place limits on the quiescent state mass flow rate in the soft X-ray transient black hole candidate source A0620-00. Specific attention is focused on the effects associated with gravitational redshifts, Doppler shifts, and on the enhancement of the apparent accretion disk area due to gravitational light bending on the continuum spectrum. It is found that the upper limit to the mass flow rate within the inner regions of the disk, constrained by the lack of soft X-rays in the quiescent state, is about 2.8 x 10 to the -11th solar mass/yr for black hole masses greater than about 5.4 solar mass. The optical data are consistent with these upper limits provided that the inclination angle of the binary system is less than about 65 deg. The upper limits and the lack of a hard X-ray flux, together, suggest that the soft X-ray transient model based upon a mass transfer instability situated in the stellar envelope of the companion is inapplicable to A0620-00.

Fu, Albert↗
NASA NTRS1990

Symmetrical jet action in the R Aquarii binary system

Collimated mass flow in opposite directions is detected in the R Aqr binary-system jet by means of high-resolution long-slit spectroscopy of several optical emission lines. Also presented are images of the jet structure in the forbidden line of O III, which clearly show bipolar symmetry extending to distances of about 2750 AU on either side of the central Mira variable. The Mira light was greatly reduced by utilization of a vignetting disk on the window of the imaging CCD. This result confirms the recent report of morphological evidence for an R Aqr jet from the detection of bipolar radio continuum emission at 6 cm, and provides the necessary kinematical evidence to show that jet action is actually taking place.

Hollis, J. M.↗
NASA NTRS2009

Eta Carinae in the Context of the Most Massive Stars

Eta Car, with its historical outbursts, visible ejecta and massive, variable winds, continues to challenge both observers and modelers. In just the past five years over 100 papers have been published on this fascinating object. We now know it to be a massive binary system with a 5.54-year period. In January 2009, Car underwent one of its periodic low-states, associated with periastron passage of the two massive stars. This event was monitored by an intensive multi-wavelength campaign ranging from -rays to radio. A large amount of data was collected to test a number of evolving models including 3-D models of the massive interacting winds. August 2009 was an excellent time for observers and theorists to come together and review the accumulated studies, as have occurred in four meetings since 1998 devoted to Eta Car. Indeed, Car behaved both predictably and unpredictably during this most recent periastron, spurring timely discussions. Coincidently, WR140 also passed through periastron in early 2009. It, too, is a intensively studied massive interacting binary. Comparison of its properties, as well as the properties of other massive stars, with those of Eta Car is very instructive. These well-known examples of evolved massive binary systems provide many clues as to the fate of the most massive stars. What are the effects of the interacting winds, of individual stellar rotation, and of the circumstellar material on what we see as hypernovae/supernovae? We hope to learn. Topics discussed in this 1.5 day Joint Discussion were: Car: the 2009.0 event: Monitoring campaigns in X-rays, optical, radio, interferometry WR140 and HD5980: similarities and differences to Car LBVs and Eta Carinae: What is the relationship? Massive binary systems, wind interactions and 3-D modeling Shapes of the Homunculus & Little Homunculus: what do we learn about mass ejection? Massive stars: the connection to supernovae, hypernovae and gamma ray bursters Where do we go from here? (future directions) The Science Organizing Committee: Co-chairs: Augusto Damineli (Brazil) & Theodore R. Gull (USA). Members: D. John Hillier (USA), Gloria Koenigsberger (Mexico), Georges Meynet (Switzerland), Nidia Morrell (Chile), Atsuo T. Okazaki (Japan), Stanley P. Owocki (USA), Andy M.T. Pol- lock (Spain), Nathan Smith (USA), Christiaan L. Sterken (Belgium), Nicole St Louis (Canada), Karel A. van der Hucht (Netherlands), Roberto Viotti (Italy) and GerdWeigelt (Germany)

Gull, Theodore R.↗