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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

The locations of Alpha-2 Herculis and Alpha-2 Scorpii along the line of sight

The theory of line formation along the line of sight to the visual companions of M stars undergoing spherically symmetric mass loss is developed. The theory is then used to determine the position of the companions relative to the primary. It is found that Alpha-2 Her is 1470 AU further along the line of sight than Alpha-1 Her for an adopted distance of 150 pc; Alpha-2 Sco is 420 AU closer than Alpha-1 Sco for an adopted distance of 185 pc.

Bernat, A. P.↗
NASA NTRS1978

Extreme-ultraviolet observations of nearby B stars - Constraints on hot circumstellar plasma

The extreme-ultraviolet telescope on the Apollo-Soyuz Test Project Mission observed several nearby stars of spectral type earlier than B3 in search of thermal emission from possible hot circumstellar plasma. The stars studied in the 45-185 and 114-185 A passbands of the instrument included Lambda Sco, Nu Sco, Beta CMa, Beta Cen, Sigma Sgr, and Alpha Pav. Diffuse emission around these stars in excess of about 1 billionth erg/sq cm/sec per sr/eV in the 45-185 A band and about 1 hundred-millionth erg/sq cm/sec per sr/eV in the 114-185 A band was not detected. The experimental data have been used to place upper limits on the emission measure of the plasma and the stellar-wind luminosity, using standard models. The data rule out the existence of sizable bubbles of hot plasma around any of the stars surveyed. In all cases the electron density in these regions, if they exist, may not exceed about 0.2 electron/cu cm.

Paresce, F.↗
NASA NTRS1979

Interstellar extinction and ultraviolet flux distribution of Scorpius X-1

Measurements of absorption at 2200 A for Sco X-1 indicate an E(B-V) of approximately 0.28. The distance to Sco X-1 is estimated to be 350 pc while the X-ray luminosity is thought to be 5 times 10 to the 36th ergs/sec. It is found that the de-reddened ultraviolet flux distribution closely resembles a blackbody at 26,000 K. Brightness variations and their relation to flickering phenomena are considered.

Wu, C.-C.↗
NASA NTRS1979

X-ray polarimetry

The method by which the Bragg-crystal X-ray polarimeters aboard Ariel 5 and OSO 8 operate is briefly described, and some results obtained with these instruments for six Galactic X-ray sources are summarized. A precision measurement of the linear polarization in the Crab Nebula at energies of 2.6 and 5.2 keV is presented. Evidence is given for polarization in Sco X-1, Cyg X-2, Cen X-3, and the X-ray transient A0620-00. The determined or estimated polarizations are approximately 19.2% at 2.6 keV and 19.5% at 5.2 keV for the Crab Nebula, 1.1% at 2.6 keV and 2.4% at 5.2 keV for Sco X-1, 2.5% at 2.6 keV and 9.8% at 5.2 keV for Cyg X-1, an upper limit of 13.5% for A0620-00, an upper limit of 13.5% to the time-averaged polarization of Cen X-3, and an apparent value of about 5% for Cyg X-2.

Long, K. S.↗
NASA NTRS1979

Bragg crystal spectroscopy on the OSO 8 satellite

Results are reported for high-resolution OSO 8 Bragg-crystal spectroscopy of a variety of cosmic X-ray sources in the energy range from 2 to 10 keV. A continuous spectrum of Sco X-1 is examined, and results of a search for narrow line emission due to iron near 6.7 keV are presented for 32 galactic X-ray sources, including Sco X-1, Cyg X-3, and Cen X-3. It is noted that the strongest evidence for iron line emission has been obtained for Cyg X-3 and that evidence for an iron line feature has also been found in the spectrum of Cen X-3.

Long, K. S.↗
NASA NTRS1979

Interstellar lines in the spectra of four stars

Observations of optical interstellar absorption lines arising from Na I, K I, and/or Ca II are reported in the spectra of HD 72127, Iota(1) Sco, 102 Her, and 6 Cas. Line components showing strikingly large Ca II/Na I ratios are found toward HD 72127 and are verified for 102 Her. The absorption toward Iota(1) Sco and 6 Cas illustrates features of the local galactic distribution of interstellar gas.

Hobbs, L. M.↗
NASA NTRS1981

The detection of interstellar fluorine in the line of sight toward Delta Scorpii

The resonance line of F I at 954.825 A is detected in the interstellar spectra of Delta Sco, and possibly Delta Ori, and upper limits are obtained toward five other stars. It is noted that the equivalent width for Delta Sco of 10.9(+4.5, -3.1) in milliangstroms corresponds to a column density of 1.52(+0.60, -0.43) x 10 to the 13th/sq cm and a depletion of -0.53(+0.15, -0.14) dex. For the other lines of sight, depletions of at least 0.1-0.5 dex are inferred. The results are discussed in the context of current theories of the depletion process.

Snow, T. P., Jr.↗
NASA NTRS1981

Evolution of X-ray astronomy

The development of X-ray astronomy, stopping short of recent observations by grazing incidence telescope, is surveyed. The discovery in 1962 of an extrasolar X-ray source, Sco X-1, with orders of magnitude stronger than astronomers believed might exist is recounted. It turned out to belong to a class of previously unknown galactic objects, the X-ray stars. The identification of a strong X-ray source with the Crab Nebula and the identification of Sco X-1 with a faint, peculiar optical object soon followed. The demonstration that X-ray stars are binary systems, each consisting of a collapsed object (a neutron star, occasionally a black hole) accreting matter from an ordinary star, and the discovery of X-ray bursts are further milestones. The discovery of exceedingly strong X-ray emission from active galaxies, quasars and clusters of galaxies and the demonstration that in these the principal X-ray source is a hot gas filling the space between galaxies sum up results.

Rossi, B.↗
NASA NTRS1981

Evolution of X-ray astronomy

The evolution of X-ray astronomy up to the launching of the Einstein observatory is presented. The evaluation proceeded through the following major steps: (1) discovery of an extrasolar X-ray source, Sco X-1, orders of magnitude stronger than astronomers believed might exist; (2) identification of a strong X-ray source with the Crab Nebula; (3) identification of Sco X-1 with a faint, peculiar optical object; (4) demonstration that X-ray stars are binary systems, each consisting of a collapsed object accreting matter from an ordinary star; (5) discovery of X-ray bursts; (6) discovery of exceedingly strong X-ray emission from active galaxies, quasars and clusters of galaxies; (7) demonstration that the principal X-ray source is a hot gas filling the space between galaxies.

Rossj, B.↗
NASA NTRS1981

Ultraviolet spectroscopy of the recurrent nova U Scorpii during outburst

Observations of the recurrent nova U Sco during the 1979 outburst are presented, and the spectral evolution is found to differ from that of other recurrent novas. Spectra are dominated by emission lines, and the strong forbidden-line emission characteristic is conspicuously absent. A method to determine masses of nova shells is outlined, and an analysis of the emission lines shows an enrichment in N relative to C and O, and that the nova ejecta are rich in He relative to H. Optical spectra of U Sco obtained following its return to quiescence show predominantly He II emission lines, which suggests an enrichment of the preoutburst gas in He, and thus the presence of a highly evolved companion.

Williams, R. E.↗
NASA NTRS1983

Long-term, hard X-ray observations of Scorpius X-1 from HEAO 1

The results of observations of Sco X-1 from three separate scanning epochs during 1977 and 1978 by the UCSD/MIT instruments aboard HEAO 1 in the 15-200 keV range are reported. Intensity and spectral variations have been studied on three time scales: 33-minute scans, daily averages, and weekly averages. No relationship was found between intensity and temperature over the very narrow range of temperatures observed, but comparison of the variability of the intensity, emission measure, and temperature implies at least two different emission mechanisms are at work. It is found that the spectral data are best fitted by either a thin-thermal-bremsstrahlung model of about 5 keV or a Comptonized thermal model of temperature about 3 keV. At higher energies (50-200 keV), no flux is found in excess of the thermal (as claimed by previous observers), and a 2-sigma upper limit from scanning data of 10 to the -5th photons/sq cm sec keV is set. This is an order of magnitude lower than reported detections. Using the distance derived from optical and UV measurements, X-ray luminosities from Sco X-1 incompatible with predictions for spherical accretion onto a white dwarf and emission volumes inconsistent with polar caps of white dwarfs are found.

Soong, Y.↗
NASA NTRS1984

Infrared observations of galactic bulge X-ray sources

Nine unidentified galactic bulge X-ray sources, the recently identified X-ray burster MXB 1728-34, and two optically identified sources (Sco X-1 and MXB 1735-44) were observed with the NASA 3 m Infrared Telescope Facility. The data constrain both the presence of diffuse infrared sources near the X-ray positions and the flux of possible infrared counterparts. None of the nine unidentified sources lies within obscured globular clusters, although there is marginal evidence for diffuse infrared emission near 4U 1822-00 and 4U 1916-05. This implies that at most two additional luminous galactic bulge X-ray sources lie within undiscovered, obscured globular clusters. No infrared counterparts were detected for unidentified sources; the limits derived are consistent with all of the sources observed being similar to the low mass X-ray binary Sco X-1.

Hertz, P.↗
NASA NTRS1984

Deuterium Abundance in the Local Interstellar Medium

The present situation of deuterium abundance evaluation in interstellar space is discussed, and it is shown that it should be or = .00001 by studying in more detail lambda the Sco line of sight and by observing two NaI interstellar components toward that star, it can be shown that the D/H evaluation made toward lambda Sco is in fact related to the local interstellar medium (less than 10 pc from the Sun). Because this evaluation is also or = .00001 it is in striking contrast with the one made toward alpha Aur (D/H or = .000018 confirming the fact that the deuterium abundance in the local interstellar medium varies by at least a factor of two over few parsecs.

Ferlet, R.↗
NASA NTRS1986

Bimodal quasi-oscillatory and spectral behavior in Scorpius X-1

Exosat observations of Sco X-1 obtained using the Xe and/or Ar detectors for a total of about 80,000 s during four runs on August 24-27, 1985 are reported and analyzed. Two modes of quasi-periodic oscillations (QPOs) corresponding to the quiescent and active states of Sco X-1 and to two modes of spectral behavior are identified and characterized, confirming the findings of Priedhorsky (1985) and Middleditch and Priedhorsky (1986). In the quiescent state, the QPO frequency is about 6 Hz and is anticorrelated with intensity, and the spectral hardness ratio (14-21 vs 2-7 keV) varies steeply with intensity; in the active state, QPO frequency is correlated with intensity and varies from 10 to 20 Hz, and the spectral-hardness-ratio/intensity curve is flatter. Previous observations of bimodal behavior in other bands are summarized, and theoretical models proposed to explain them are discussed.

Priedhorsky, W.↗
NASA NTRS1987

Search for orbital X-ray variation in Scorpius X-1

All 5 yr of 3-6 keV monitoring of Sco X-1 by the Ariel 5 all-sky monitor have been reanalyzed to search more sensitively for variation at the 0.787313 d orbital period. The best limits on orbital variations come from data selected to exclude active episodes. Any narrow absorption dip has an average depth less than 1.0 percent (0.1/Delta Phi), where Delta Phi is the width in units of the orbital period (2 sigma confidence level). A weak (0.4 percent) sinusoidal modulation, with 3.2 sigma significance, reaching minimum at phase 0.59 + or - 0.06 with respect to superior conjunction of the optical emission-line source is observed. In any case, the upper limit to a sinusoidal orbital modulation is 0.7 percent. Sco X-1 never - at least not for more than 2 hrs - dipped below its normal quiescent level.

Priedhorsky, W. C.↗
NASA NTRS1987

Correlation between spectral state and quasi-periodic oscillation parameters in GX 5-1

In a series of seven Exosat observations, the bimodal spectral behavior and the quasi-periodic oscillation (QPO)/red noise properties of GX 5-1 show a strict correlation. In one of the two spectral states (characterized by a 'horizontal branch' in the hardness-intensity diagram), strong 20-40 Hz QPO and red noise below about 60 Hz were always present. In the other ('normal branch'), no QPO between 6 and 60 Hz or red noise above 1 Hz were detected, but there was an indication for weak QPO near 5 Hz. In both states 'very low frequency noise' (VLFN) is detected below 0.1 Hz which has a power-law shape and and which extends down to the lowest observed frequencies (0.0001 Hz). The VLFN is probably not directly related to the QPO. The results are compared to those on Sco X-1 and Cyg X-2 and it is concluded that, although all three sources show bimodal spectral and QPO/red noise behavior, there is a qualitative difference between GX 5-1 and Cyg X-2 on one hand and Sco X-1 on the other.

Van Der Klis, M.↗
NASA NTRS1990

Orbital periods of recurrent novae

The class of recurrent novae (RN) with thermonuclear runaways contains only three systems (T Pyx, U Sco, and V394 CrA), for which no orbital periods are known. This paper presents a series of photometric observations where the orbital periods for all three systems are discovered. T Pyx is found to have sinusoidal modulation with an amplitude of 0.08 mag and a period of 2.3783 h (with a possible alias of 2.6403 h). U Sco is found to be an eclipsing system with an eclipse amplitude of roughly 1.5 mag and an orbital period of 1.2344 days. V394 CrA is found to have sinusoidal modulation with an amplitude of 0.5 mag and a period of 0.7577 days. Thus two out of three RN with thermonuclear runaways (or five out of six for all RN) have evolved companions.

Schaefer, Bradley E.↗
NASA NTRS1990

IUE observations of galactic and extragalactic recurrent novae

A collection of International Ultraviolet Explorer (IUE) light curves and sample spectra for the galactic recurrent novae observed in the ultraviolet are presented. These data are compared to that of the Nova LMC (Large Magellanic Cloud) 1990 number 2 which is shown to also be a recurrent novae. Based on the analysis of the outburst of N LMC 1990 number 2 it is suggested that all of the recurrent novae observed in the ultraviolet have luminosities at maximum light which exceed the Eddington limit. V745 Sco and RS Oph, the two recurrent novae with late type giant companions, show strong Mg II throughout the outburst. Those with low luminosity companions, U Sco and V394 CrA do not show Mg II but do show strong He II 1640 earlier in the outburst. Typical emission line velocities are greater than those observed in many of the classical novae. These characteristics suggest that the white dwarfs in recurrent novae systems are close to the Chandrasekhar limit.

Shore, Steven N.↗