500 – 3200 Å observations of the interacting binary stars V356 Sgr and β Lyr

In this paper we present new results from the Voyager ultraviolet spectrometers and the IUE spacecraft on V356 Sgr and β Lyr. The V356 Sgr observations cover, in detail, two eclipses and include one IUE high dispersion SWP image. During both eclipses the total strength of the UV emission lines were found to be invariant. Also, an uneclipsed UV continuum was detected at wavelengths shorter than 1600 Å. The IUE high dispersion SWP spectrum revealed that the emission lines are extremely broad, almost symmetrical lines with weak, slightly blue shifted absorption components. No evidence of carbon is seen in the emission or absorption spectrum of V356 Sgr in eclipse. A model for the origin of the circumstellar matter in this binary system is presented. The Voyager ultraviolet observations of β Lyr show a strong far-UV continuum that is detectable down to 912 Å The far-UV continuum flux level was variable on time scales shorter than the orbital period and displayed no obvious orbital modulation or eclipses. The spectral shape of the far-UV continuum closely resembles that of a UX UMa type cataclysmic variable. On 16 August 1985 an rapid brightening of the far-UV continuum was observed which was also reminiscent of cataclysmic variables. Analysis of the β Lyr data suggest that the central object must be small, with a radius on the order of 1 R_⊙ or less.     

X-ray variability of the bright BL Lac object PKS 2155-304

We have observed the BL Lac object PKS 2155-304 with the EXOSAT observatory and with IUE on 1983 October 31 and November 29. At the same time, optical photometry has been obtained. Variability has been observed both on a time scale of hours during the October 31 observation and on the time scale of one month. During the November 29 observation the source was 2 times brighter than in the previous observation, but no spectral modification is found between the two observations. The source has been also detected in the ME instrument and an energy spectrum has been fitted with a power law. A marginal detection in the ME Xenon counters suggests a flattening of the spectrum in the high energy band. These X-ray data extending over three decades in energy are compared with the simultaneous UV and optical observations.     

EXOSAT observations of the contact binary VW Cephei

EXOSAT observations of the contact binary VW Cephei on 19th March 1984 are presented. The L1-telescope with CMA+thick Lexan filter was used. The observations cover one orbital revolution showing an asymmetrical X-ray light curve. This can be modelled by an active neck, connecting the two stars, and with enhanced coronal regions on the primary star. Nearly simultaneous IUE observations are also presented. The observations form a part of the program to observe contact binaries with EXOSAT.     

EXOSAT observations of late-type stars: The application of coronal loop models

We apply solar-type coronal loop models to X-ray and UV observations of late-type stars. We derive from EXOSAT and IUE observations constraints on the temperature, pressure and size of the emitting structures.     

Matter streams in Algol-like systems

Simulations of the Algol-like binary CX Draconis, combined with IUE observations of the stream of material escaping the system can place limits on the inclination of the system and give estimates, via line profile synthesis, of the mass-loss rate at the L1 point.     

Matter streams in Algol-like systems

Simulations of the Algol-like binary CX Draconis, combined with IUE observations of the stream of material escaping the system can place limits on the inclination of the system and give estimates, via line profile synthesis, of the mass-loss rate at the L1 point.     

An optical outburst from the periodic recurrent X-ray transient A0538-66

We present optical spectroscopy and photometry and IUE spectroscopy of the counterpart of the LMC recurrent X-ray transient A0538-66 during an outburst at the end of December 1980 which was consistent with the 16.6 day X-ray period (Skinner, 1980). The optical spectra show steadily increasing Balmer and HeI emission (indicative of a shell phase) superposed on a B2 IV spectrum with a substantial brightness increase of 2^m and the sharp turn-on of HeII 686 at the peak. Significant radial velocity changes have been detected but they show no correlation with the 16.6 day period. IUE spectra during a subsequent outburst show very strong and broad (5000 km s^–1) emission from C IV 1550 and HeII 1640. This behaviour is compared with other galactic transients and shell/Be stars.     

O-star winds in the Magellanic Clouds and the Milky Way

UV P-Cygni profiles of OB-stars in the Magellanic Clouds (observed with HST), and the galaxy (observed with IUE) are analyzed empirically using a line formation procedure similar to the one described by Lamers et al. (1987). The assumption of a constant microturbulencev _turb throughout the wind is dropped and replaced by a radially increasing turbulence parameterv _turb(v), thus improving the fit for the emission peaks substantially, and at the same time avoiding the need for a justification of extremely supersonic turbulence in the vicinity of the wind's sonic point. The Sobolev optical depth is determined interatively at fixed velocities in the wind, which removes the bias introduced by the choice of a specific parameterization function. Where it was possible and necessary a full photospheric spectrum was used to illuminate the wind line. The terminal velocitiesv are are found to be largest in the Galaxy, smallest in the Small Magellanic Cloud, and intermediate or similar to galactic in the Large Cloud.     

An optical and ultraviolet survey of Algols

We present a-table of results from our survey of Algols, conducted with the Lick Observatory ITS scanners and the IUE spectrometer.We have determined the continuous flux distributions for a number of the Algol systems. Optical scans were made with the ITS scanners of Lick Observatory, while for the ultraviolet flux distributions, we used the IUE satellite spectrometer in the low-dispersion mode. The following table summarizes the results: {ie340-01}     

The atmospheric composition,extinction and luminosity of the LBV R71

ESO 3.6m Caspec spectra of the LMC luminous blue variable (LBV) taken at minimum have been analysed using NLTE model atmospheres and line formation calculations to derive atmospheric parameters and chemical composition. Using the silicon ionization balance and the hydrogen Balmer lines we deriveT _eff =17250, log g=1.80 and a microturbulent velocity of 15–20 km/s. The analysis yields abundance ratios by number of approximately 0.43 for He/H, 0.03 for C/N and 0.14 for O/N, implying that enrichment of the atmosphere by processed material has taken place. We have re-evaluated the reddening of R71 using IUE low resolution data and published UBVRIJHKL photometry and derive a value for A _V of 0.63. We also construct an extinction curve using archive IUE data for mid-B LMC supergiants and show that the extinction is anomalous; the 2175A bump being almost absent and the far UV rise very pronounced. A comparison of our model flux in theV-band with the observed (dereddened)V magnitude and the D.M. of the LMC (18.45), implies that the bolometric magnitude or R71 is –9.9. This is significantly higher than the value of –9.0 usually adopted for R71 and suggests that this object may not in fact be a subluminous LBV.     

An optical and ultraviolet survey of Algols

We present a-table of results from our survey of Algols, conducted with the Lick Observatory ITS scanners and the IUE spectrometer. We have determined the continuous flux distributions for a number of the Algol systems. Optical scans were made with the ITS scanners of Lick Observatory, while for the ultraviolet flux distributions, we used the IUE satellite spectrometer in the low-dispersion mode. The following table summarizes the results: {ie340-01}     

A catalogue of low-resolution IUE spectra of dwarf novae and nova-like stars

A catalogue is presented of all the low-resolution IUE spectra of dwarf novae and nova-like stars that were recorded until the end of 1987. All spectra have been reduced, and are displayed, in a homogeneous way. In addition to details about these data, to the extent available, their position in the outburst light curves is given, physical information about each system, and a comprehensive list of references for published observations in all wavelength ranges.     

A catalogue of low-resolution IUE spectra of dwarf novae and nova-like stars

A catalogue is presented of all the low-resolution IUE spectra of dwarf novae and nova-like stars that were recorded until the end of 1987. All spectra have been reduced, and are displayed, in a homogeneous way. In addition to details about these data, to the extent available, their position in the outburst light curves is given, physical information about each system, and a comprehensive list of references for published observations in all wavelength ranges.In collaboration with Janet A. Mattei, American Association of Variable Star Observers, 25 Birch Street, Cambridge, MA 02138-1205, U.S.A.     

A catalogue of low-resolution IUE spectra of dwarf novae and nova-like stars

A catalogue is presented of all the low-resolution IUE spectra of dwarf novae and nova-like stars that were recorded until the end of 1987. All spectra have been reduced, and are displayed, in a homogeneous way. In addition to details about these data, to the extent available, their position in the outburst light curves is given, physical information about each system, and a comprehensive list of references for published observations in all wavelength ranges.In collaboration with Janet A. Mattei, American Association of Variable Star Observers, 25 Birch Street, Cambridge, MA 02138-1205, U.S.A.     

Ultraviolet observations of the X-ray sources in the ETA garinae Nebula

Car is surrounded by a dense nebula ejected during the last 150 years. The Einstein satellite recently detected intense X-ray emission from Car and its nebula indicating the existence of efficient gas heating processes. Ultraviolet observations with IUE confirmed the presence of hot gas in the condensation S of the nebula and in Car. Possible interpretations of the results are discussed.Based on observations by the International Ultraviolet Explorer made at the Villafranca Satellite Tracking Station of the European Space Agency.     

Doppler tomography of O-type binaries: The physical properties of seven systems

We have analyzed UV photospheric lines of seven O-type binaries, by means of crosscorrelation and Doppler tomographic methods, with the goal of estimating the physical properties of the individual stars. These systems are HD 1337 (AO Cas), HD 47129 (Plaskett's star), HD 57060 (29 UW CMa), HD 37043 (Iota Ori), HD 215835 (DH Cep), HD 152218, and HD 152248. Mass ratios have been obtained primarily from a cross-correlation technique, but also by several other techniques. The tomographic techniques allow us to separate the spectra of the components. We then can estimate the individual spectral types and luminosity classes of the stars (and henceT _eff and logg, respectively), the luminosity ratio, and projected rotational velocities. We discuss the physical properties of these O-type binaries. These are some of the early results of a large scale project involving 36 O-type double-lined binary systems (from the catalog of Battenet al. 1989) which we will study using IUE and complementary ground-based data.     

Deuterium Observations in the Galaxy

An accurate measurement of the primordial value of D/H would provide one of the best tests of nucleosynthesis models for the early Universe and the baryon density. Such evaluations have been traditionally made using present estimations of the deuterium abundance in the interstellar medium, extrapolated backwards in time with the use of galactic evolution models. Direct estimations of the primordial deuterium abundance have been carried out only recently in QSOs absorbers at high redshift.We will summarize galactic observations of deuterium and suggest that, perhaps, a single D/H value for the interstellar medium is not representative. These evaluations mainly came from observations completed in the far UV with first the Copernicus satellite over the Lyman lines series followed then by H and D Lyman-alpha lines observations with both the IUE and the GHRS on the Hubble Space Telescope. We discuss different known systematics and show that the situation is not yet clear. It is not possible today to claim that we know "the" D/H value in the interstellar medium, if any.Overall and in the context of additional D observations made in the solar system, we conclude that the actual evolution of deuterium from Big-Bang nucleosynthesis to now is not yet understood. More observations, recently made with IMAPS (the Interstellar Medium Absorption Profile Spectrograph) and hopefully to be made with FUSE (the Far Ultraviolet Spectroscopic Explorer to be launched in the fall of 1998), at higher spectral resolution or in many different galactic sites are certainly needed to help us reach a better global view of the evolution of that key element, and thus better constrain any evaluation of its primordial abundance.     

Hubble Space Telescope spectroscopy of massive hot stars in the Magellanic Clouds and M31

Using the Hubble Space Telescope (HST) and the Faint Object Spectrograph (FOS) high signal to noise spectrograms were obtained for 15 OB stars in the Magellanic Clouds^***, three of which are of spectral type O3. The data cover the spectral region from 1150 A – 2300 A with a resolution of /1 A. One O8.5 supergiant, OB78#231, in M31is also included in this work. These data are a substantial improvement on previous high resolution IUE observations in the Magellanic Clouds (Walborn et al. 1985 and references therein) because of the smaller aperture and the much better signal to noise ratio, while no high resolution UV spectra of O stars in M31 have been obtained before. In this paper we discuss various morphological aspects of the spectra, concerning metallicity and the stellar winds, compared to galactic analogues.     

Joint Ulysses and ACE observations of a magnetic cloud and the associated solar energetic particle event

On day 49 of 1999 a strong interplanetary shock was observed by the ACE spacecraft located at 1 AU from the Sun. This shock was followed 10 hours later by a magnetic cloud (MC). A large solar energetic particle (SEP) event was observed in association with the arrival of the shock and the MC at ACE. The Ulysses spacecraft, located at 22° S heliolatitude and nearly the same ecliptic longitude as ACE, observed a large SEP event beginning on day 54 that peaked with the arrival of a solar wind and magnetic field disturbance on day 61. A magnetic cloud was observed by Ulysses on days 63–64. We suggest a scenario in which both spacecraft intercepted the same MC, although sampling different regions of it. We describe the effects that the MC produced on the streaming of energetic particles at both spacecraft. This revised version was published online in August 2006 with corrections to the Cover Date.