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Chromospheres of Two Red Giants in NGC 6752
Smith, Graeme H.; Dupree, A. K.; Jordan, Carole +3 more
Two red giant stars, A31 and A59, in the globular cluster NGC 6752 exhibit Mg II (2800 A) emission with surface fluxes comparable to those observed among metal-deficient halo field giants, and among low-activity Population I giants. Optical echelle spectra of these cluster giants reveal emission in the core of the Ca II K (3933.7 A) line, and in t…
Period Measurements of the 50 Millisecond Pulsar PSR 0540-69 with the EXOSAT Satellite
Hasinger, Guenther; Oegelman, Hakki
The period of the 50 ms pulsar PSR 0540 - 69 in the Large Magellanic Cloud was determined using five separate X-ray observations with the Exosat satellite in the interval August 12, 1984 to June 30, 1985. Together with Einstein observations and contemporaneous optical data, the Exosat periods can be fitted well to a quadratic curve yielding a brak…
The Complex 0.4--12 keV X-Ray Spectrum of Cygnus X-1
van der Woerd, H.; Barr, P.
Simultaneous observations of the 0.4-2 keV and 2-12 low-state spectrum of Cygnus X-1, made with the low-energy transmission grating spectrometer and gas scintillation proportional counter on board EXOSAT, are presented. At least four spectral components are required to describe the data: a hard (energy spectral index alpha about 0.4) power law dom…
High-velocity gas components towards 4 Lac.
Keenan, F. P.; Bates, B.; Catney, M. G.
A comparison of IUE ultraviolet spectra of the star 4 Lac with observations of a suitable comparison star have confirmed the presence of 'high-velocity gas components' in the former which are redshifted by a velocity about 100 km/s from the low-velocity interstellar gas. In addition to providing an unambiguous identification of the species which s…
Analysis of the COS B Data for Evidence of Linear Polarization of VELA Pulsar Gamma Rays
Mattox, John R.; Mayer-Hasselwander, Hans A.; Strong, Andy W.
The COS B spark chamber telescope observations of the Vela pulsar were analyzed for gamma-ray polarization. No significant quadrupole moment is found in the azimuthal distribution of the electron-positron pair production planes. However, analysis of the sensitivity indicates that even 100-percent polarization would not be detected. Therefore, the …
Is V426 Ophiuchi really an intermediate polar ?
Hellier, Coel; O'Donoghue, Darragh; Buckley, David +1 more
The dwarf nova V426 Oph has been proposed as an intermediate polar with a report of a 60-min period in the X-ray band. Optical photometry and spectroscopy show no evidence for such a period. Additionally, reanalysis of the X-ray data shows that the 60-min period is not significant and that the variability is consistent with flickering. Overall, no…
The High-Luminosity BL Lacertae Object PKS 0823-22
Falomo, Renato
Simultaneous infrared, optical, and UV observations of the BL Lacertae object PKS 0823-22 are presented. The identification of the observed absorption doublet at λλ5341, 5355 with Mg II λλ2796, 2803 gives an absorption redshift z_abs_ = 0.910. At this redshift, the object is one of the most luminous of its class with M_V_ <~ -29.4. The spectral…
Detection of Trace Helium in G104-27, a 26,000 K DA White Dwarf
Wesemael, F.; Holberg, J. B.; Kidder, K. M.
The detection of the He I 4471 A feature in the moderately hot DA white dwarf G104 - 27 places this star within the rather sparse class of DAB white dwarfs. It does not appear possible, on the basis of the present data, to distinguish between a stratified and a homogeneously mixed atmosphere. While a stratified structure would be natural for a DA …
EXOSAT observation of the supernova remnant MSH 15-52.
Hasinger, G.; Aschenbach, B.; Brinkmann, W. +3 more
The results of an Exosat observation of the supernova remnant MSH 15-52 and of the pulsar PSR 1509-58 are presented and discussed. In the energy range 1.6-11 keV, the radiation flux of the nebula surrounding the pulsar detected by the ME instrument has been fitted with a power law spectrum with index alpha about 1.86 (photon spectrum) and column d…
IUE observations of mass-loss spectral features in B5-B9 supergiants.
Bates, B.; Gilheany, S.
A survey of IUE spectra is presented for supergiants of spectral class B5-B9 illustrating the behavior of line profiles associated with mass-loss effects. The main purpose of this survey is to better identify the spectral mass-loss features which occur in such stars in order to present a clearer observational picture of the nature and the timescal…