Search Publications

The absolute magnitudes of RR Lyrae stars - III. DH Peg.

Jameson, R. F.; Fernley, J. A.; Skillen, I. +1 more

UV optical and IR photometry of the RRc Lyrae star DH Peg is presented. Using this photometry plus previously published data the IR Flux Method of Blackwell & Shallis (1977) is applied to estimate effective temperatures and angular diameters at all phases of the pulsation cycle. The angular diameters are then matched with the integrated radial…

The X-ray orbital lightcurve of TY Pyx : a 3.2-day eclipsing RS CVn system.

Parmar, A. N.; White, N. E.; Culhane, J. L. +1 more

An Exosat observation of one orbital cycle of the eclipsing 3.2-d RS CVn system TY Pyx is reported. This system contains two almost identical GV stars, which is unusual because most RS CVns contain F or G main-sequence star and a K subgiant. The X-ray light curves of the primary and secondary eclipses are different above and below 1 keV. At lower …

X-ray spectral variations in NGC 4151.

Perola, G. C.; Fiore, F.; Romano, M.

In their analysis of the EXOSAT ME data on the Seyfert NGC 4151, Yaqoob, Warwick & Pounds found that the observed tendency of the spectrum to soften as the X-ray flux increases is due to variations in the absorbing column, which are anti-correlated with the source intensity, thus favouring a 'warm absorber' model. In this paper a re-analysis o…

Coronal X-ray emission from the short-period eclipsing binary XY UMa.

Jeffries, R. D.; Bedford, D. K.; Vilhu, O. +1 more

XY UMa, a close binary showing photospheric and chromospheric activity, has been observed with Exosat through 1.26 orbital cycles, with supporting optical photometry. The G2-5 V primary star is found to be responsible for the observed soft X-ray flux, which shows a clear primary eclipse. The X-ray-emitting coronal plasma is modeled to have two com…

Photospheric absorption lines in the UV spectra of O and B type stars.

Prinja, R. K.

Measurements of the equivalent widths of ultraviolet photo spheric lines of He II λ1640, C III λ1247, N III λλ1748, 1752, O IV λ1339, Si II λ1265, Si III λ1299, Si III λ1417, Si IV λλ1394, 1403 and Fe IV λ1765 in O3 to B5 stars are presented, using high-resolution IUE spectra of 300 supergiant, giant and dwarf stars.

All the ions exhibit a we…

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…

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…

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…

Effective temperatures of RCB stars.

Evans, A.; Bode, M. F.; Albinson, J. S. +1 more

IUE observations and optical-IR photometry are reported for a number of R Coronae Borealis stars, including the LMC object W Men. Non-line-blanketed, hydrogen-deficient model atmospheres are normalized to the data in the IR to determine effective and color temperatures. By comparing stellar flux distributions with model atmosphere calculations, wa…

Self-consistent comptonized models for the spectra of low-mass X-ray binaries.

Ross, R. R.; Ponman, T. J.; Foster, A. J.

We have constructed Comptonized spectral models and fitted them to EXOSAT spectra of eleven bright low-mass X-ray binaries. The models are based on the premise that these systems contain circumstellar material which modifies the X-ray spectrum passing through it. We idealize this situation as a point source of X-rays, the neutron star, embedded in…