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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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NASA NTRS1973

UHURU results on galactic X-ray sources.

Consideration of the nature of the galactic X-ray sources located with the aid of the UHURU satellite. A brief description is given of the X-ray emission of the Galaxy as a whole. The general properties of sources similar to Sco X-1 (called Sco X-1-like sources) are discussed, as well as the properties of three pulsating sources showing evidence of a binary nature. Finally, some new results concerning two objects - GX263+3 (2U0900-40) and the X-ray source in the Small Magellanic Cloud (2U0115-73) - which both show evidence of a binary nature, yet have some of the properties of the Sco X-1-like objects are presented. The links noted between the Sco X-1-like objects and the pulsating binary sources lead to the suggestion that all of the galactic X-ray sources (except supernova remnants) may in fact be binaries.

Tananbaum, H. D.↗
NASA NTRS1975

A search for stellar soft X-ray sources

A sensitive soft X-ray survey of about one-tenth of the sky, carried out as part of the Skylab program and flown on 1973 July 28, revealed no evidence for soft X-ray emission from stellar sources. We present upper limits to the soft X-ray luminosity of about 50 nearby stars. With nominal assumed values for stellar space densities, we show it unlikely that emission from giants, main sequence stars, white dwarfs, or stars in known binary systems can account for the soft X-ray diffuse background.

Vanderhill, M. J.↗
NASA NTRS1975

Combined optical and X-ray observations of variable stars

Questions concerning the optical identification of X-ray sources are considered. There are now a total of eight optically identified galactic X-ray sources. Of these eight, five are definitely established as binaries. The nature of the other three sources remains unknown. Studies of U Geminorum conducted on the basis of optical and X-ray observations are also discussed. From the upper limit to the accretion rate for U Gem obtained with the aid of soft X-ray data, it is seen that most of the mass flow in U Gem is lost from the system.

Bowyer, C. S.↗
NASA NTRS1973

Spectroscopic observations of the optical candidate for Cygnus X-1.

The spectroscopic binary BD+34 3815 (= HDE 226868) with a period of 5.6 days, which is the brightest object in the position box for the X-ray source Cyg X-1, is studied to determine whether it meets all the requirements for being a black hole. Evidence is presented that the mass of the secondary is larger than the upper limits for white dwarfs or neutron stars, but there is no conclusive evidence that the optical binary is an X-ray source, and that the secondary is a collapsed object.

Brucato, R.↗
NASA NTRS1975

What is special about Cygnus X-1 - Black holes in theory and observation: X-ray observations

Of the eight X-ray sources now known which may be associated with binary stellar systems, Cygnus X-1 is the most likely candidate for being a black hole. The X-ray evidence from several experiments is reviewed, with special emphasis on those characteristics which appear to distinguish Cygnus X-1 from other compact X-ray emitting objects. Data are examined within the context of a model in which millisecond bursts (Rothschild et al., 1974) are superposed on shot-noise fluctuations (Terrell, 1972) arising from 'events' of durations on the order of a second. Possible spectral-temporal correlations are investigated which indicate new measurements that need to be made in future experiments.

Boldt, E.↗
NASA NTRS1975

Optical and X-ray observations of the PSR 1913 + 16 field

We have obtained medium-resolution spectra in the yellow of seven stars in the error box of the binary radio pulsar PSR 1913 + 16, using the image-tube scanner at the Lick 3-m telescope. None of the objects is spectroscopically abnormal and thus a strong candidate for membership in the system. The data are used to establish the extinction in the field, which is modest for this low galactic latitude. For three of the stars, limits of the order V exceeding 23 mag on optical pulsations with the frequency of the radio pulsar are derived. X-ray observations of the field have been obtained in the 2.5-7.5 keV band, using the UCL experiment aboard OAO Copernicus. No source is detected, with a 2 sigma upper limit on the time-averaged flux of 1.0 times 10 to the -10th power ergs per sq cm per sec.

Davidsen, A.↗
NASA NTRS1972

Evidence for the binary nature of Centaurus X-3 from Uhuru X-ray observations.

Analysis of data spanning a year of observations of the pulsating X-ray source Cen X-3 from Uhuru has revealed the existence of periodic variations in intensity of the source and correlated sinusoidal variations in the period of the 4.8-sec pulsations. We interpret this effect as due to an occulting binary system. The changes in intensity are then due to occultation of the X-ray source by a large massive companion, and the sinusoidal variations in the period of the 4.8-sec pulsations are due to Doppler effect. Physical parameters for the system are derived, and evidence for the existence and nature of an extended atmosphere surrounding the massive occulting object is discussed.

Schreier, E.↗
NASA NTRS1975

New results from long-term observations of Cyg X-1

Observations of Cyg X-1 between October 1974 and July 1975 reveal a persistent 5.6 day modulation of the 3 to 6 keV X-ray intensity, having a minimum in phase with superior conjunction of the HDE 226868 binary system. The modulation is found to be most pronounced just prior to the April-May 1975 increase of Cyg X-1, after which both the modulation and intensity are at their lowest values for the entire duration of the observations. These data imply that the X-ray emission from Cyg X-1 arises from the compact member of HDE 226868, and that the increase of April-May 1975 may have represented the depletion of accreting material which was not mixed into a cylindrically symmetric accretion disk about the compact member.

Holt, S. S.↗
NASA NTRS1975

Ultraviolet observations of alpha Aurigae from Copernicus

Emission lines of L-alpha (1215.67 A) and O VI (1031.94 A) were detected in the spectroscopic binary alpha Aur (Capella) with the Princeton experiment on Copernicus. Temperatures of the emitting regions are inferred to be in excess of 300,000 K. The temperature and emission measure are consistent with a variable source of soft X-rays. If the emission is attributed to the primary star (G5 III), the atmosphere is expanding with velocities of about 20-100 km/s. Such expansion can lead to material within the binary system. The density of interstellar hydrogen inferred from absorption of stellar L-alpha appears to be approximately 0.01 hydrogen atoms per cu cm.

Dupree, A. K.↗
NASA NTRS1974

Galactic X-ray sources

Data on galactic X-ray sources from rocket and balloon experiments and the UHURU satellite are reported. The outline emphasizes general discrete source models and begins with some a priori considerations about X-ray emission mechanisms and their applicability, after which contemporary data are interpreted according to these models. Topics covered include the production of X-rays by various mechanisms, source regimes, observational parameters, stellar distributions, individual stars, flare stars, supernovae and pulsars, the Crab nebula, old and young remnants, binary systems, and others.

Holt, S. S.↗
NASA NTRS1974

Observations of Circinus X-1 from Uhuru

Analysis of Uhuru observations of the X-ray source Cir X-1 (3U 1516-56) suggests that the source may be a binary with a period longer than 15.0 days. Significant intensity variations have been observed on all time scales from 0.1 sec to days. Changes in the X-ray energy spectrum from 2 to 20 keV have also been found. A refined X-ray position, containing no obvious optical counterpart, is reported. The similarities between Cyg X-1 and Cir X-1 suggest that the X rays from Cir X-1 may be produced by accretion onto a massive, collapsed object.

Jones, C.↗
NASA NTRS1975

Triaxial degenerate dwarfs and pulsing X-ray sources

It is shown that triaxial configurations for rotating degenerate dwarfs consisting entirely of fluid are not limited to forms analogous to the Jacobi ellipsoids. Arguments are presented which rule out only the specialized class of uniformly rotating analogs of the Jacobi ellipsoid for some degenerate dwarfs. Several ways of forming triaxial degenerate dwarfs are examined along with the characteristic lifetimes of such objects. Noting that some of the alternative forms may exist in mass-transfer binary systems, consideration is given to the secondaries in Her X-1 and Cen X-3. It is suggested that the secondary in Her X-1 must be close to an analog of a Dedekind ellipsoid, and plausible triaxial white-dwarf configurations are proposed for the secondary in Cen X-3.

Durisen, R. H.↗
NASA NTRS1975

Intense soft X-ray flux from Hercules X-1

An intense flux of soft X-rays extending up to at least 1 keV has been observed from Her X-1. If the soft X-ray intensity is corrected for interstellar absorption, the luminosity in the 0.16-0.28 keV band is comparable to that from 2 to 10 keV. This confirms the conclusion of Shulman et al. (1975) but extends the detection of this flux to higher energy, a different binary phase, and to a time 19 periods later in the 35-day cycle. These observations suggest that this soft emission may be a stable feature in the spectrum of Her X-1 during its X-ray on state. It appears difficult to account for the high soft X-ray luminosity by current simple models of the X-ray source.

Catura, R. C.↗
NASA NTRS1972

Optical candidates for two X-ray sources.

Suggestion of the bright stars X Per and HD 77581 as possible candidates for the X-ray sources 2U 0352+30 and 2U 0900-40 respectively. The first is an active, rapidly rotating Be star which is losing mass. The second is similar to BD+34.3815 deg, a likely candidate for Cyg X-1, in spectral type and in the possibility that it may be a short-period binary.

Brucato, R. J.↗
NASA NTRS1973

High energy and solar astronomy, overview

A survey of our own galaxy and neighboring galaxies using X-rays, gamma rays, and cosmic rays is outlined. High energy astrophysic results suggest the presence of a new acceleration mechanism where the inflow of matter on collapsed objects seems to be one of the sources of complex time variations in binary systems.

Mcdonald, F. B.↗