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NASA NTRS1972

X-ray fluorescence experiment

The preliminary results from the Sco X-1 and Cyg X-1 obtained from the Apollo 15 X-ray detector data are presented along with preliminary results of the X-ray fluorescence spectrometric data of the lunar surface composition. The production of the characteristic X-rays following the interaction of solar X-rays with the lunar surface is described along with the X-ray spectrometer. Preliminary analyses of the astronomical X-ray observation and the X-ray fluorescence data are presented.

Adler, I.↗

NASA NTRS1972

Mg II 2800 A emission in late type stars

The largest body of data on ultraviolet spectra of late-type stars now available is the series of scans made with the long wavelength spectrometer onboard OAO-2. Some features of selected scans from this series and estimates of Mg II emission fluxes were reported earlier. Since that time, the effects of sky background, scattered light and variable instrumental sensitivity have become better understood. Additional stars are used to define more clearly the transition from Mg II 2800 A absorption to emission with advancing spectral type, and additional scans of alpha Sco provide a better estimate of Mg II emission strength for this supergiant in OAO observations.

Doherty, L. R.↗

NASA NTRS1972

Ultraviolet observations of weak-helium stars

Ultraviolet filter photometry aboard OAO-2 has been carried out for the weak helium stars 3 Cen A, 3 Sco, HD 144334, HD 21699, HD 144844, alpha Scl, HR 8535, HR 8770 and HD 144661. The flux distribution is compared with that of B3 to B8 main sequence and giant stars in terms of color-color diagrams. When allowance is made for line blocking shortward of 2800 A that most of the weak helium stars have normal fluxes in good agreement with their ground-based colors. The star alpha Scl is a light and spectrum variable. The strengthening of Ti II and Sr II lines around 2400 A appears to redistribute flux longward of the Balmer discontinuity. The flux distribution indicates an effective temperature about 1500 K higher than previously determined.

Bernacca, P. L.↗

NASA NTRS1971

A Bragg spectrometer for stellar X-ray astronomy.

Poor energy resolution and the steeply varying continuum spectrum make it impossible to obtain with proportional counters an unambiguous identification of certain emission features of Sco X-1. For this reason a Bragg crystal spectrometer was constructed. The instrument, flown successfully aboard an Aerobee-170 rocket, scanned the spectral range from 2.4 to 2.9 keV. The spectrometer consists of two large reflecting crystals of synthetic graphite. The results obtained during the flight of the instrument clearly indicate that the Bragg method can yield much higher sensitivity to line emission than can proportional counter methods.

Kestenbaum, H.↗

NASA NTRS1971

A large area Thomson-scattering stellar X-ray polarimeter.

An instrument for measuring the polarization of stellar X-ray emission has been designed, constructed, and tested. The polarization dependence of incoherent Thomson scattering in lithium metal is utilized. Means for suppression of cosmic ray background effects have been provided. The apparatus has been flown in rockets to obtain data in the polarization of X-ray sources in Sco X-1 and Tau X-1.

Novick, R.↗

NASA NTRS1972

The UHURU X-ray instrument.

On Dec. 12, 1970, the UHURU X-ray observatory was launched into equatorial orbit with the prime mission of conducting an all-sky survey of astronomical X-ray sources with intensities of 0.00005 Sco-X1 or greater. The X-ray detection system contains 12 gas-filled proportional counters, 6 behind each collimator. The aspect system is discussed together with the structure, the pulse height analyzer, the command system, the calibration system, and the power distribution system. Pulse shape discrimination circuits used on UHURU use the same technique that was used on the system originally developed for large area proportional counters described by Gorenstein and Mickiewicz (1968).

Jagoda, N.↗

NASA NTRS1972

Nature of the secondary component of beta Lyrae.

Development of a hypothesis concerning the nature of the secondary component of beta Lyrae which is regarded as more plausible than the suggestion that this component is a black hole. Adopting Huang's (1962) and Woolf's (1965) basic model for beta Lyrae, it is suggested that the secondary star may be a massive 'main-sequence' star in rapid, nonuniform motion. Certain findings regarding mu Sco and V356 Sgr, which have primaries that are very cool and underluminous for their masses, are cited as evidence for such an inference, since their underluminosity is probably due to high angular momentum and they are normal enough not to be suspected of harboring a black hole.

Stothers, R.↗

NASA NTRS1972

A sealed titanium window proportional counter for the detection of .5-keV X rays.

A sealed Ti window proportional counter sensitive to X radiation in the energy range 0.35-0.45 keV and above 1.5 keV is described. Measurements of the Ti mass absorption coefficients and a graphical summary of the literature values are presented. For a proportional counter with a 930 microgram/sq cm (2.1-micron) Ti window, the peak efficiency at 0.45 keV is found to lie between 4.6% and 7.1%. An application in X-ray astronomy involving a rocket observation of Sco X-1 is discussed.

Mcclintock, J. E.↗

NASA NTRS1972

The interstellar molecular hydrogen observed in the ultraviolet spectrum of delta Scorpii

Molecular hydrogen bands of the Lyman and Werner systems were observed in the ultraviolet, interstellar spectrum of delta Sco. The average molecular column density is given, and the average temperature of the gas of which the molecules are part is 47 K. Minimum and maximum gas temperatures are 25 and 98 K respectively. The ratio of the number of hydrogen atoms in molecular form to the total number of hydrogen atoms in either atomic or molecular form is 0.044 (+0.070, -0.018).

Smith, A. M.↗

NASA NTRS1972

X-ray fluorescence experiment

The X-ray fluorescence spectrometer, carried in the scientific instrument module bay of the command and service module, was used for orbital mapping of the lunar surface composition and X-ray galactic observations during transearth coast. The lunar surface measurements involved observations of the intensity and characteristic energy distribution of the secondary or fluorescent X-rays produced by the interaction of solar X-rays with the lunar surface. The astronomical observations consisted of relatively long periods of X-ray measurement of preselected galactic sources such as Cygnus (Cyg X-1) and Scorpius (Sco X-1).

Adler, I.↗

NASA NTRS1973

Properties of optical radiation of variables and quasars

Photoelectric observations in the system UBV are considered for 42 variable stars, six quasars and Sco XR-1 with U-B and B-V colors of different type radiations. There are regressive dependences for nearly all the objects. On the Delta V/Delta B, Delta U/Delta B plane the objects were divided according to the types and situated along the bands. The directions of these bands are in agreement with values of A for different types of radiation.

Lukatskaya, F. I.↗

NASA NTRS1973

Possible explanation for nonthermal radio noise from binary stars.

Radio emission from the binary stars alpha-Sco, beta-Per, and beta-Lyr is interpreted as due to the mass exchange between the components. The electrons in the inflowing stream excite plasma waves near the surface of the receptor star, and these waves generate radio emission. Crude predictions of radio frequency, intensity, and timescales of variation seem compatible with current observations.

Jones, T. W.↗

NASA NTRS1973

Hard cosmic X-ray sources.

A review of the observational status of X-ray sources detected in the 20 to 500 keV range is presented. Of the approximately 115 sources listed in the March 1972 edition of the UHURU 2-6 keV sky survey catalog, about 15 sources have been studied in hard X rays. Most of the data have been obtained from balloons, although the OSO-3, and more recently the OSO-7, have contributed. With the exception of CEN A, the SMC, and possibly M-87, all the sources detected at higher energies are galactic and heavily concentrated in the galactic plane. The Crab Nebula has been measured to about 500 keV in continuous emission and a component at the 33-msec pulsar period comprising about 20% of the total emission has been detected to 10 MeV. Objects such as SCO-1 and CYG-2 are characterized by an exponential spectrum, which varies over a 10-min time scale about a factor of two, and a flatter spectrum extending to above 40 keV which exhibits independent variability.

Peterson, L. E.↗

NASA NTRS1973

Long-term X-ray observations of Scorpius X-1 by OSO-III.

Review of the observations of Scorpius X-1 in the energy range 7.7-22 keV provided by the X-ray telescope on the OSO-III satellite over the period from May 19 to June 13, 1967. Optical observations representative of the full range of temporal behavior of the source are available on 10 nights during this period. Sco X-1, in spite of being the most extensively observed X-ray source, remains one of the least understood. Coordinated observations in various wavelength bands, although inconclusive so far, represent potentially the most fruitful approach.

Pelling, R. M.↗

NASA NTRS1973

Study of optical properties of X-ray sources

A report is presented of R and D of the optical properties of X-ray sources. The topics discussed include: (1) simultaneous optical and X-ray observations; (2) coronal line search in cygnus loop; (3) Her X-1=HZ Her observations; (4) Cyg X-1 observations; and (5) Sco X-1 radio companion observations.

Vandenbout, P. A.↗

NASA NTRS1974

Investigation of ultraviolet fluxes of normal and peculiar stars

Data from Project Celescope, a program that photographed the ultraviolet sky, in order to study several problems in current astrophysics are analyzed. Two star clusters, the Pleiades and the Hyades, reveal differences between the two that we are unable to explain simply from their differences in chemical abundance, rotation, or reddening. Data for Orion show large scatter, which appears to be in the sense that the Orion stars are too faint for their ground-based photometry. Similarly, many supergiants in the association Sco OB1 are too faint in the ultraviolet, but the ultraviolet brightness appears to be only poorly correlated with spectral type. Ultraviolet Celescope data for several groups of peculiar stars have also been analyzed. The strong He I stars are too faint in the ultraviolet, possibly owing to enhancement of O II continuous opacity due to oxygen overabundance. The Be stars appear to have ultraviolet colors normal for their MK spectral types. The P Cygni stars are considerably fainter than main-sequence stars of comparable spectral type, probably owing, at least in part, to line blocking by resonance lines of multiply ionized light metals. The Wolf-Rayet stars have ultraviolet color temperatures of O stars.

Deutschman, W. A.↗

NASA NTRS1974

The spectral types of the members of VV Cephei systems from photometric analysis

The photometric data for ten binary systems that have a highly luminous red primary with a less luminous blue companion have been analyzed, and the spectral types of the member stars have been determined. Eight of these systems are VV Cephei-type systems; one, alpha Sco, has a more distant blue companion, while XX Per has a blue companion that is probably too distant to induce emission. It has been determined that the blue companion of WY Gem is an intrinsic variable.

Wawrukiewicz, A. S.↗

NASA NTRS1974

The nature of Cygnus X-3 - A prototype for old population binary X-ray sources

Description of a model for Cyg X-3 based on a short-lived phase in the evolution of a U Geminorum-type binary where rapid mass transfer and mass loss occurs. X rays are generated by accretion on the white dwarf component, while both stars are enveloped in a thick stellar wind emanating from the red dwarf. Electron scattering in the cloud is responsible for the modulation of the X rays with the orbital period of 4.8 hours. Ultraviolet radiation and low-energy X rays absorbed in the cloud are reradiated in the optical and infrared, which, it is predicted, will display a 4.8-hr modulation in phase with the X-ray light curve. The X-ray absorption cutoff should also vary with phase, appearing at minimum energy when the source is at maximum light. The model also provides a framework in which certain aspects of the associated nonthermal radio source may be understood. Finally, it is suggested that the model may be applicable to Sco X-1 as well.

Davidsen, A.↗