Absolute gamma-ray intensity measurements of a SNAP-15A heat source
SNAP 15A heat source gamma ray intensity measurements and identification of gamma ray producing isotopes, describing measurement apparatus
Reier, M.↗
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Spectra of type I supernovae. I - Generalities. II - Interpretation of the spectra of Sn 1960 in NGC 4496 from 8 to 20 days after the maximum of luminosity.
In the late stages of type I supernovae evolution (t greater than 50 days) the spectrum is without doubt an emission line spectrum, but in the early stages it is difficult to tell if an emission line spectrum is observed, or a continuum spectrum modified by the overlaying absorption formed in the outer layers. The mechanism of formation of the observed spectra, the physical conditions in the shell, different possible sources of heating of the shell, identification of the lines, and theoretical computations of the line intensities are discussed. An attempt is made to interpret the set of spectra assuming that a spectrum of widely broadened emission lines truncated by an overlaying absorption is seen. The absorption spectrum is first studied. An identification for the emission lines is proposed, and their intensity on the observed spectra is tentatively estimated. These identifications have to be justified by the theoretical computations of a model of the shell.
Gordon, C.↗
The peculiar star He 2-177 - A slow nova and a possible X-ray source
The remarkable detail resemblence of the spectrum of the peculiar emission-line star He 2-177 to that of the slow nova RR Telescopii is illustrated by tabulated data and discussed. The evolution of the spectrum since 1965 closely resembles the evolution of RR Tel between 1951 and 1954. A newly determined position of X-ray source 2U 1639-62 makes its identification with He 2-177 less probable than before.
Carlson, E. D.↗
Optical and X-ray observations of 3U 0614+09
Based on positional agreement, ultraviolet excess, and spectroscopic peculiarity, the identification of the X-ray source 3U 0614+09 with a faint blue star, previously suggested by Murdin et al. (1974) as a candidate, is established. Four days of X-ray observations at 1-3 A failed to show evidence for significant variability or eclipses. The possibility that this object may be very similar to Sco X-1, but at a distance of 4-8 kpc, is discussed.
Davidsen, A.↗
Feige 24 - A very hot white dwarf
OAO-2 ultraviolet photometry of the composite spectrum white dwarf Feige 24 is compared with model atmospheres to derive an effective temperature of 70,000 (+20,000, -15,000) K. The distance to this star is estimated to be 90 (+55, -31) pc if the cool component is assumed to be a main-sequence star with a red and near-infrared energy distribution that is normal for its spectral type. The derived characteristics of Feige 24 are compatible with its identification as the extreme-ultraviolet source observed by Margon et al.
Holm, A. V.↗
The X-ray light curve of AM Herculis
Observations by SAS 3 during 1976 show that the soft X-ray flux of 3U 1809+50 is modulated with the same period as the optical phenomena of AM Her. The identification of the X-ray source with AM Her is thus confirmed. It is found that the X-ray source undergoes a total eclipse with a duration of approximately 0.15 period. The heliocentric epoch of the eclipse center is JD 2,442,919.636, which is at phase 0.5 relative to the primary optical minimum and coincides with a secondary optical minimum.
Hearn, D. R.↗
X-ray observations of BL Lac objects
The BL Lac objects MK501 and MK421 have been observed by the HEAO-1 experiment A-2 in the 2-60-keV band. Their spectra are similar with best-fitting power laws having an energy index between -0.2 and 0.2. There was no detectable X-ray absorption with implied column densities of less than 1.5 x 10 to the 22nd H atoms/sq cm. MK421 was a factor 6 weaker in November 1977 then in May 1977. A new identification of PKS0548-322 with a source near 4U 0543-31 is suggested.
Mushotzky, R. F.↗
Discovery of a soft X-ray flux from AN Ursae Majoris
During November 1975, the soft X-ray detectors on the SAS 3 satellite scanned across AN Ursae Majoris, a star very similar to AM Herculis in its unusual optical properties. A soft (0.1-0.4 keV) X-ray flux averaging 2.8 x 10 to the -11th erg/sq cm-sec was detected from AN UMa, as had been anticipated by analogy with AM Her. Folding the X-ray flux measurement with the known binary period reveals an X-ray light curve with approximately 100% modulation, and thereby secures the identification of the X-ray source as AN UMa. Unlike the case in AM Her, the X-ray minimum in AN UMa occurs midway between optical linear-polarization peaks.
Hearn, D. R.↗
Discovery of low-redshift X-ray selected quasars - New clues to the QSO phenomenon
The identification of six X-ray sources discovered by the Einstein Observatory with X-ray quasars is reported, and the properties of these X-ray selected quasars are discussed. The four high-latitude fields of 1 sq deg each in which the Einstein imaging proportional counter detected serendipitous X-ray sources at intermediate exposures of 10,000 sec were observed by 4-m and 1.5-m telescopes, and optical sources with uv excesses and emission line spectra typical of many low-redshift quasars and Seyfert 1 galaxies were found within the 1-arcsec error boxes of the X-ray sources. All six quasars identified were found to be radio quiet, with low redshift and relatively faint optical magnitudes, and to be similar in space density, colors and magnitude versus redshift relation to an optically selected sample at the same mean magnitude. X-ray luminosity was found to be well correlated with both continuum and broad-line emission luminosities for the known radio-quiet quasars and Seyfert 1 galaxies, and it was observed that the five objects with the lowest redshifts have very similar X-ray/optical luminosity ratios despite tenfold variations in X-ray luminosity. It is concluded that photoionization by a continuum extending to X-ray energies is the dominant excitation mechanism in radio-quiet quasars.
Grindlay, J. E.↗
Goldstone radio spectrum signal identification, March 1980 - March 1982
The signal identification process is described. The Goldstone radio spectrum environment contains signals that are a potential source of electromagnetic interference to the Goldstone tracking receivers. The identification of these signals is accomplished by the use of signal parameters and environment parameters. Statistical data on the Goldstone radio spectrum environment from 2285 to 2305 MHz are provided.
Gaudian, B. A.↗
Discovery of a 50 minute binary period and a likely 22 magnitude optical counterpart for the X-ray burster 4U 1915-05
Absorption dips which recur with a period of 2985 s have been observed from the X-ray burst source 4U 1915-05. It is suggested that the dips are caused by obscuration of the X-ray source by material at the point where the gas stream from the companion meets the accretion disk, and that the 2985 s periodicity is the orbital period of the binary system. These observations represent the first direct evidence of the binary nature of X-ray burst sources. In addition, a new optical identification of 4U 1915-05 is suggested: a 22 magnitude candidate observed in a CCD image of the optical field at the arcsec-accurate HRI X-ray position.
Walter, F. M.↗
Studies of BL Lacertae objects with the Einstein X-ray observatory - The absolute volume density
It is estimated that the local volume density of BL Lac objects which emit greater than 10 to the 44th ergs/s in the 0.5-4.5 keV band is about 10 to the -7th/cu Mpc. This is based on identifications of bright X-ray sources, and the fact that Einstein X-ray observations detect BL Lac objects over a wide, continuous range of flux up to the thresholds of the all-sky X-ray surveys. Since this density is of the same order of magnitude as the local density of Seyfert galaxies, or local density of optically selected quasars, emitting X-rays at the same luminosity, we argue that the difference between these particular astronomical classifications is not solely due to the orientation of a relativistic beam.
Schwartz, D. A.↗
1E 0104.2 + 3153 - A broad absorption-line QSO viewed through a giant elliptical galaxy
The optical identification of the X-ray source 1E 0104.2 + 3153 is complicated by the close projection of a broad absorption-line (BAL) QSO (z = 2.027) 10 arcsec from a giant elliptical galaxy (z = 0.111) at the center of a compact group of galaxies. At only 1.2 de Vaucouleur radii (16 kpc for H sub 0 = 100 km/s Mpc) this QSO-galaxy projection is the closest yet discovered. Based upon current observations, the source of the X-ray emission cannot be conclusively determined. Present in the BAL QSO spectrum are extremely strong Ca II H and K absorption lines due to the intervening galaxy, the first optical detection of the cold interstellar medium in an elliptical galaxy. The strength of these lines (EW = 2 and 1 A) requires observation through several interstellar clouds in the line of sight to the QSO. By its proximity to the central regions of the elliptical galaxy and the relative distances of the galaxy and QSO, this QSO is a particularly good candidate for observing dramatic transient gravitational lensing phenomena due to halo stars in the foreground galaxy.
Stocke, J. T.↗
Nitrogen on Triton
The tentative identification of liquid nitrogen as the source of the 2.16-micron absorption band in the spectrum of Triton has suggested a surface model in which nitrogen, together with the previously identified methane, occur in some kind of chemical association. Water frost may be another surface chemistry component, and dark, photochemically-produced particles occur as a minor contaminant of the ices or liquid. Temperature is noted to be a critical factor in the surface model, because the calculated subsolar surface temperature of Triton lies near nitrogen's melting-freezing temperature. The present modeling of Triton suggests nitrogen's occurrence in the form of fine grains.
Clark, R. N.↗
Identification of the SiCC radical toward IC +10216 - The first molecular ring in an astronomical source
In the radio spectrum of the envelope of the evolved carbon star IRC +10216, the fraction of lines from exotic molecules seldom or never observed in the terrestrial laboratory is exceptionally high. At least 20 lines have not been identified, and it is not known whether one, two, or a number of new molecules are involved. It is shown in the present investigation that nine of the previously unidentified lines in IRC +10216 are produced by SiCC, a radical long known to exist in stellar atmospheres. The true ground-state geometry of this radical has only been obtained recently on the basis of an elegant two-photon ionization experiment in a supersonic molecular beam. Information regarding the molecular geometry and lower rotational levels of SiCC is presented in a graph. The intensities of the SiCC lines confirm the assignments, yield new data on the temperature and density in the envelope of IRC +10216, and indicate that the amount of SiCC there is substantial.
Thaddeus, P.↗
Operating characteristics of a prototype high energy gamma-ray telescope
The field of gamma-ray astronomy in the energy range from ten to several hundred MeV is severely limited by the angular resolution that can be achieved by present instruments. The identification of some of the point sources found by the COS-B mission and the resolution of detailed structure existing in those sources may depend on the development of a new class of instrument. The coded aperture mask telescope, used successfully at X-ray energies hold the promise of being such an instrument. A prototype coded aperture telescope was operated in a tagged photon beam ranging in energy from 23 to 123 MeV. The purpose of the experiment was to demonstrate the feasibility of operating a coded aperture mask telescope in this energy region. Some preliminary results and conclusions drawn from some of the data resulting from this experiment are presented.
Jenkins, T. L.↗
X-ray variability of BL Lac objects - H2155-304 and PKS 0548-322
X-ray emission from two BL Lacertae objects (H2155-304 and PKS 0548-322) has been studied with the High-Resolution Imager and Monitor Proportional Counter (MPC) on the Einstein Observatory. The high-spatial-resolution observations confirm the identification of these X-ray sources with the BL Lac objects and give a source size less than about 2 arcsec. Variations in the X-ray intensity and spectrum of these sources were detected over time scales of a few hours from analysis of the MPC observations.
Agrawal, P. C.↗
IRAS observations of matter around nearby stars
A systematic search of the IRAS point-source catalog has led to the identification of eight new nearby stars that are Vega-like in terms of their large 60-micron excess. These stars are distinguished by the predominance of spectral type A and the absence of double stars in the Vega-like group. Both effects are intuitively consistent with the interpretation that the 60-micron excess radiation is due to a disk of protoplanetary material, suggesting an early phase in the evolution of a planetary system; however, this distribution can also be due to luminosity and brightness selection effects.
Aumann, H. H.↗