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The spectrum of the planetary nebula IC 351
Feibelman, Walter A.; Hyung, Siek; Aller, Lawrence H.
International Ultraviolet Explorer (IUE) and optical region spectroscopic observations are presented for the moderately high-excitation planetary nebula IC 351. Most of the atoms are distributed over a narrow range of ionization. Thus [NII] and [SII] are weak; [NeIV] is prominent, but [NeV] is missing. It appears that the metal/hydrogen ratio is s…
The ultraviolet polarization of the Crab pulsar
Lyne, A. G.; Dolan, J. F.; Boyd, P. T. +3 more
The linear polarization of the Crab pulsar has been observed in the ultraviolet using the High Speed Photometer on the Hubble Space Telescope. The polarization as a function of pulse phase is strikingly similar to that observed in the visible, with the same values of fractional polarization and the same swing of position angle occurring through th…
The extreme-ultraviolet spectrum of the central star of the planetary nebula NGC 1360
Dreizler, Stefan; Drake, Jeremy J.; Werner, Klaus +1 more
We have used the Extreme Ultraviolet Explorer (EUVE) to obtain the first EUV spectrum of the central star of a planetary nebula, that of NGC 1360. The photospheric spectrum shows continuum absorption edges due to O^4+ as well as absorption-line features. NLTE model atmospheres including line blanketing by iron-group elements can match the general …
The variable mass loss of the peculiar supergiant P Cygni.
Sterken, C.; Israelian, G.; Parker, J. W. +1 more
The study of iron lines from 49 high-resolution IUE spectra observed in the period of 1985-1991 allowed us to find a repetition time between two successive shells of the order of six months. We found that absorption lines of Fe III often have two components while Fe II lines can have three. P Cygni is the only luminous blue variable that does not …
Non-LTE model chromospheres of zeta Aurigae stars
Marshall, K. P.
Plane-parallel, one-component, non-local thermodynamic equilibrium (LTE), semi-empirical model chromospheres have been constructed for the primary stars in the zeta Aurigae systems HR 6902 and 22 Vul. This has been accomplished by means of radiative transfer calculations undertaken with a non-LTE multilevel radiative transfer code, MULTI, and curv…
HD 159176: photospheric and wind-dominated light-curve analyses coupled to wind modelling
Pachoulakis, Ioannis
HD 159176 is a hot, massive, non-eclipsing binary with a small-amplitude ellipsoidal variability. The existing velocity solution determines the ratio of the stellar masses. In the present article these radial velocities, coupled with one optical and two UV light curves derived from IUE images in bandpasses devoid of stellar wind lines, are solved …
The binary Cepheid W Sgr.
Cottrell, P. L.; Albrow, M. D.
High-resolution spectra have been obtained over a seven-year period for the 7.6 d binary Cepheid W Sgr. Radial velocities measured from these spectra have been combined with those measured with the CORAVEL radial velocity spectrometer and a new orbital solution obtained with the parameters P = 1603 d, K = 1.90 km s-1, e = 0.42. Velociti…
The origin of the correlation between the UV and X-rays in NGC 4151
Zdziarski, Andrzej A.; Magdziarz, Pawel
We propose that the UV/X-ray correlation observed in NGC 4151 by EXOSAT and IUE is due to re-emission of the X-ray flux absorbed by cold clouds in the line of sight. This transmission model satisfies the energy balance, provides a good fit to the X-ray and UV data, and predicts no Compton reflection of X-rays (as observed). Alternatively, the corr…
The narrow variable components of CIV in NGC 4151 from 1981 to 1987
Ulrich, M. -H.
The nucleus of the Seyfert 1 galaxy NGC 4151 undergoes large-amplitude variations and occasionally passes through deep minimum states lasting up to a few months. Two narrow emission lines, L_1 and L_2, variable in intensity on a time-scale of a few days were discovered during International Ultra-violet Explorer (IUE) campaigns at low states in 198…
Further optical and UV spectroscopy of stars in the direction of the Riegel & Crutcher cold cloud
Hambly, N. C.; Bates, B.; Kemp, S. N.
Further optical and UV spectral data are presented for four stars in the direction of the Riegel & Crutcher cold cloud. Two of the stars lie close in position to the area covered by our previous optical, UV and radio studies near l=10 deg, while the other two stars lie near l=15 deg. The stars range in distance from about 140 pc to 1.5 kpc. Th…