Search Publications
Activity in F Stars
Simon, Theodore; Boesgaard, Ann Merchant; Wolff, Sidney C.
Measurements of He I 5876 A and IUE measurements of chromospheric and transition region lines in a large sample of F-type stars are presented. The data show that activity is detectable in nearly all early F-type stars and differs in several of its characteristics from that typically seen in cooler stars with slow rotation and fully developed conve…
Coordinated Exosat and spectroscopic observations of flare stars and coronal heating
Foing, B. H.; Rodono, M.; Butler, C. J. +1 more
The X-ray flux of dMe stars is thought to arise from two distinct mechanisms, one involving a continuous `quiescent' emission from a high-temperature plasma and the other involving the dramatic flare events which have long been known to occur on these stars. We present here some results of simultaneous monitoring of the two flare stars, UV Ceti an…
The discovery of X-ray bursts from CIR X-1.
Fabian, A. C.; Tennant, A. F.; Shafer, R. A.
A sequence of eight X-ray flares was detected during an EXOSAT observation of the low-state Circinus X-1 (= BR Cir). The authors identify these flares with X-ray bursts from Cir X-1. The recurrence time, ratio of persistent flux to the time-averaged flux and indications of cooling during the bursts are all consistent with these bursts being type I…
The chemical composition of NGC 2363.
Pena, M.; Torres-Peimbert, S.; Peimbert, M.
Photoelectric spectrophotometry in the 3400 - 7400 Å is presented for the metal-poor extragalactic H II region NGC 2363. Based on these data, on IUE observations and on ionization structure models the authors have obtained the chemical abundances. The C/O ratio is a factor of two smaller than in the solar vicinity and under reasonable assumptions …
The soft X-ray spectrum of NGC 4151.
Culhane, J. L.; Warwick, R. S.; Pounds, K. A. +1 more
EXOSAT observations of the Seyfert galaxy NGC 4151 over the period 1983 July - 1984 April have revealed a steeply decreasing flux in the 2 - 10 keV band. Other observations have shown that this coincided with a fall in the whole infrared-to-ultraviolet continuum and a marked weakening of the broad emission lines. The X-ray spectral shape, however,…
The Discovery of 3.9 Hour Periodic Dips in the X-Ray Intensity of XB 1254-690
Parmar, A. N.; Pakull, M.; Courvoisier, T. J. -L. +1 more
The low-mass X-ray binary XB 1254 - 690 has been discovered to show irregular dips in X-ray intensity that recur with a period of 3.9 hr consistent with the optical period derived independently. The spectral changes observed during dipping are complex and can be successfully described using a two-component model. One of these components may be X-r…
The empirical BC versus T EFF scale for non-supergiant O9-G5 stars.
Morossi, C.; Malagnini, M. L.; Rossi, L. +1 more
By the analysis of observed energy distributions extending from the UV to the IR, the effective temperature, the gravity and the bolometric correction for a representative sample of nonsupergiant and not chemically peculiar O9-G5 stars are derived in a self-consistent way. The new, improved relationship between the bolometric correction and the ef…
Post-perihelion observations of water in comet Halley
Weaver, H. A.; Davis, D. S.; Mumma, M. J. +1 more
Our previous pre-perihelion observations1 of comet Halley from the NASA Kuiper Airborne Observatory (KAO) resulted in the first definite detection of water vapour in a comet. This success allowed us to carry out an ambitious post-perihelion KAO observing programme which significantly extended the scope of our Halley water investigation.…
Chromospherically active stars. II. HD 82558, a young single BY Draconis variable.
Fekel, F. C.; Simon, T.; Bopp, B. W. +4 more
It is presently noted that the HD 82558 chromospherically active star is a young and rapidly rotating K2 V single BY Draconis variable with very strong far-UV emission features and an H-alpha line filled to the continuum level by emission. HD 82558 has constant velocity and is not a member of the Hyades Supercluster. Its light curve behavior, whic…
Spectral similarities in the visible and UV spectrum of Herbig Ae/Be stars.
Catala, C.; Czarny, J.; Felenbok, P. +1 more
High resolution spectroscopic observations of pre-main sequence Herbig Ae/Be stars in the P Cygni subclass are reported. The observations were carried out in order to determine whether the envelopes of the stars belonging to the same spectral subclass are similar. The specific stars observed were: HD 250550; BD 46 deg 3471, and HD 150193. The H-al…