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Dwarf novae in outburst : simultaneous ultraolet and optical observations of UZ Serpentis, RX Andromedae and AH Herculis.
Verbunt, F.; Schwarzenberg-Czerny, A.; Jones, D. H. P. +6 more
The authors present spectroscopic and photometric observations in the optical and ultraviolet wavelength regions made during outbursts of the three dwarf novae UZ Serpentis, RX Andromedae and AH Herculis. The observations do not cover the rapid initial rise to outburst, but rather the peak and the subsequent decline. The overall changes of the con…
The abundance of interstellar chlorine in the galaxy.
Bromage, G. E.; Harris, A. W.
The results of a large-scale survey of chlorine abundance in interstellar H I gas are presented. The abundances are derived from measurements of 40 interstellar-absorption-line equivalent widths in far-ultraviolet stellar spectra from the Copernicus and International Ultraviolet Explorer (IUE) satellites. It is found that the relative chlorine abu…
EXOSAT observations of GH 2215^-086 : detection of the X-ray pulse period
Watson, M. G.; McHardy, I. M.; Cook, M. C.
A 2.8 hr observation of the intermediate polar H2215 - 086 using the Exosat Medium Energy experiment has revealed a strong, quasi-sinusoidal modulation of the hard X-ray flux with a period (20.65 + or - 0.32 min) consistent with, and in phase with, that of the large amplitude optical variations. The detection of this hard X-ray modulation confirms…
Spectral and temporal features in bursts from 2S 1636-536 observed with EXOSAT.
Turner, M. J. L.; Breedon, L. M.
The well-known X-ray burster 2S 1636-536 (Nor X-1) was observed for 7 hr by the ME instrument on EXOSAT. During this time 7 bursts of unusual shape were detected. The bursts have similar profiles. The results suggest that each burst has two components with an initial helium thermonuclear flash triggering a stronger hydrogen flash; the ratio of con…
Optical photometry and ultraviolet spectroscopy of the flare/BY DRA star GL 182(V 1005 Ori).
Doyle, J. G.; Butler, C. J.; Byrne, P. B.
G1 182 was previously reported to be a rapidly rotating BY Dra star which flares at an anomalously high rate. The present observations confirm its BY Dra nature but revise the rotation period, such that it is shown to rotate much more slowly. The time-averaged energy output in flares is shown to be normal for a flare star of its spectral type, and…
Ultraviolet spectra of planetary nebulae - X. Physical conditions in the compact planetary nebula SW ST 1.
Cohen, M.; Flower, D. R.; Goharji, A.
The authors analyse photoelectric visual and ultraviolet observations of the compact planetary nebula Sw St 1. The electron density, determined from the C III λλ1907/1909 line ratio, is Ne = (1.1±0.1)×105cm-3, consistent with the high emission measure and high critical frequency determined from observations of the …
IUE observations of high velocity interstellar gas toward stars within the OB association CYG OB1.
Pettini, M.; Phillips, A. P.; Welsh, B. Y.
High-velocity interstellar gas has been detected in IUE spectra of the stars HD 192639, 193514 and 193443 which are members of the OB association Cyg OB1. In all cases where blending between different absorption components is not severe, the authors have derived ion column densities appropriate to the high-velocity gas by fitting theoretical profi…
Observations of narrow absorption components in the ultraviolet spectrum of zeta Ophiuchi.
Howarth, I. D.; Willis, A. J.; Prinja, R. K.
Narrow absorption components due to the resonance transitions of C IV and N V are noted to be present in all 33 high resolution IUE spectra of Zeta Ophiuchi obtained between 1978 and 1981, though Doppler shifted by -1385 km/sec. An examination of previous observations shows these features to have been present for at least 12 years, and it is deter…
IUE observations of the X-ray binary A0538-66 : spectroscopic study of a strange stellar system.
Howarth, I. D.; Willis, A. J.; Prinja, R. K. +1 more
The results of extensive IUE monitoring of the optical counterpart of the recurrent periodic LMC X-ray transient A0538-66 are presented. Even when the system is not in outburst dramatic spectral variations occur, accompanied by changes in the temperature and surface area of the continuum emitting region. It is shown that, in spite of these variati…
SI III emission line strengths in low density plasmas.
Dufton, P. L.; Keenan, F. P.; Kingston, A. E.
Theoretical emissivity ratios appropriate to homogeneous optically thin plasmas are presented for the Si III lines at 1883 and 1892 Å. These lines are a useful density diagnostic for Ne ≥ 104cm-3, their use being illustrated for the planetary nebulae NGC 7662 and V1016 Cygni.