Search Publications
The Exotic Helium Variable PG 1346+082
Winget, D. E.; Wesemael, F.; Liebert, James +5 more
The results of an extensive study of the blue object PG 1346 + 082, which is both a photometric and a spectroscopic variable, are presented. The system spans the B magnitude range 13.6-17.2, is brighter than m(pg) of about 14.0 roughly 74 percent of the time, and has a photometric quasi-period of four to five days. The rapid photometric flickering…
CAL 83: A Puzzling X-Ray Source in the Large Magellanic Cloud
Thompson, I. B.; Crampton, David; Hutchings, J. B. +3 more
Spectroscopic observations of the X-ray point source no. 83 in the Columbia Astrophysics Laboratory Einstein survey of the Large Magellanic Cloud have been accumulated over 4 yr. The optical spectrum shows no stellar absorption features, but only emission lines typical of an accretion disk. Radial velocity measurements reveal a small (K = 30 km/s)…
Periodic Photospheric and Chromospheric Modulation in Alpha Orionis (Betelgeuse)
Sonneborn, G.; Dupree, A. K.; Guinan, E. F. +3 more
The bright cool supergiant Alpha Orionis has been monitored spectroscopically and photometrically over the past three years (1984-1986) in the optical and the ultraviolet wavelength regions. A 420-day periodic modulation of the flux is observed in the optical and ultaviolet continua, and in the Mg II line emission cores. Periodic photospheric puls…
X-Ray Sources in Regions of Star Formation. II. The Pre--Main-Sequence G Star HDE 283572
Roth, M.; Linsky, J. L.; Walter, F. M. +7 more
This paper reports the detection of HDE 283572, a ninth-magnitude G star 8 arcmin south of RY Tau, as a bright X-ray source. The observations reveal this object to be a fairly massive (about 2 solar masses) pre-main-sequence star associated with the Taurus-Auriga star formation complex. It exhibits few of the characteristics of the classical T Tau…
EXOSAT Observations of 4U 1705-44: Type I Bursts and Persistent Emission
Hasinger, G.; Gottwald, M.; Sztajno, M. +2 more
During four Exosat observations, the bright galactic X-ray source 4U 1705-44 exhibited persistent emission variations from 1.3 to 10.7 x 10 to the -9th ergs/sq cm per sec in the 1-20 keV band. Type I X-ray bursts have been detected from this source whose properties correlate with source intensity. The burst shape changed with increasing intensity …
Spectroscopy of the Rapidly Rotating K Star HD 36705
Gustafsson, B.; Edvardsson, B.; Vilhu, O.
Spectroscopic observations of HD 36705 are reported. Values of 100 + or - 5 km/s and 29 + or - 2 km/s are derived for the v sin i and radial velocity, respectively. The central wavelength of the broad H-alpha emission varies as a function of rotation phase with an amplitude of 16 km/s and with the maximum redshift at the photometric minimum. Using…
Simultaneous Multifrequency Observations of the BL Lacertae Object Markarian 421
Koyama, K.; Matsuoka, M.; Kondo, Y. +26 more
Simultaneous multifrequency observations of the BL Lac object Mrk 421 covering radio through X-ray wavelengths were performed on two occasions separated by 5 weeks in January and March 1984, and each observation was coordinated for about 1 week. Composite multifrequency spectra of the central nonthermal component were obtained at the two epochs af…
Correlation between Spectral State and Quasi-periodic Oscillation Parameters in GX 5-1
van Paradijs, J.; van der Klis, M.; Lewin, W. H. G. +3 more
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 pres…
IUE Observations of Hydrogen and Deuterium in the Local Interstellar Medium
Moos, H. W.; Murthy, J.; Linsky, J. L. +4 more
The authors present and analyze high-dispersion IUE observations of the interstellar hydrogen and deuterium Lyα absorption profiles toward the late-type stars ɛ Eri (3.3 pc), Procyon (3.5 pc), Altair (5.1 pc), Capella (13.2 pc), and HR 1099 (33 pc). They derive values for the density nH I, the velocity dispersion bH I, the bu…
Broad, Variable Absorption Lines in the Seyfert Galaxy NGC 3516: Probing the Structure of the Emssion-Line Regions
Voit, G. Mark; Shull, J. Michael; Begelman, Mitchell C.
Nineteen short-wavelength IUE archive images were analyzed in order to probe the structure of the active nucleus in NGC 3516, an SB0 Seyfert I galaxy. The measurements of these features are presented, and the strength, variability, and morphology of the emission and absorption lines and their relation to the continuum are analyzed. It is shown tha…