Search Publications
Multi-site continuous spectroscopy. II. Spectrophotometry and energy budget of exceptional white-light flares on HR1099 from the MUSICOS 89 campaign.
Zhang, X.; de La Reza, R.; Keskin, V. +48 more
We report results from the December 89 multi-site continuous observing campaign (MUSICOS 89) dedicated to the study of surface active structures and flares on the RS CVn-type system HR1099 (=V711 Tau). This system has been observed by up to 17 telescopes around the globe during this campaign. We obtained complete phase coverage for Doppler imaging…
The IMF and the extinction law in M 101: HST FOS spectra of extragalactic HII regions.
Benvenuti, P.; Rosa, M. R.
We present medium resolution HST FOS spectra of the ionizing star clusters in four giant HII regions in the spiral galaxy M101, spanning a range in [O/H] from 8.2 to 8.9. The observed energy distributions in the wavelength range 1150A to 8200A are compared to population synthesis models of extremely young star clusters, taking into account the att…
Interplanetary type III radio bursts that approach the plasma frequency: ULYSSES observations.
Hoang, S.; Leblanc, Y.; Dulk, G. A.
We study a set of solar type III radio bursts where the emission is visible from the high-frequency limit of the radio astronomy receiver of the Ulysses Unified Radio and Plasma wave (URAP) experiment down to low frequencies, sometimes near the plasma frequency, and where Langmuir wave spikes are recorded by the radio and/or plasma receivers. For …
HST observations of globular clusters in M 31 I. Surface photometry of 13 objects.
Cacciari, C.; Federici, L.; Ferraro, F. R. +8 more
We present the initial results of a study of globular clusters in M 31, using the Faint Object Camera (FOC) on the Hubble Space Telescope (HST). The sample of objects consists of 13 clusters spanning a range of properties. Three independent image deconvolution techniques were used in order to compensate for the optical problems of the HST, leading…
Lower chromospheric activity in low activity M dwarfs
Doyle, J. G.; Mathioudakis, M.; Houdebine, E. R. +1 more
Four low activity dM(e) stars Gl 105B, Gl 643, Gl 813 and Gl 821 were observed spectroscopically in the optical and ultraviolet regions. Despite relatively long integrations, only one of the four had detectable Ca II K&H emission, Gl 821, which had an observed flux of 9 10^-15^ erg/cm2/s, giving a surface flux of only 0.8 10^4^ erg/cm2/s. Simi…
Analysis of ROSAT pointed observations of 15 hot DA white dwarfs.
Wolff, B.; Jordan, S.; Koester, D. +1 more
We present the results of pointed observations of hot white dwarfs with the ROSAT PSPC detector, and through the P1 filter of the Wide Field Camera. Model atmospheres containing hydrogen and helium, either homogeneously mixed or chemically stratified, are used to analyze the new data together with observations of the same objects by EXOSAT and the…
Rotational modulation and flares on RS Canum Venaticorum and BY Draconis stars. XVIII. Coordinated VLA, ROSAT, and IUE observations of RS CVn binaries .
Schmitt, J. H. M. M.; Bromage, G. E.; Pagano, I. +8 more
As part of a coordinated program of multi-wavelength observations of RS CVn close binary systems, we observed 15 systems with the VLA and 10 systems with IUE, simultaneously or nearly simultaneously with the ROSAT All Sky Survey observations of these stars. Of the 22 systems observed with ROSAT, three were observed both by IUE and the VLA. The pri…
The EUV spectrum of AU Microscopii: temperature and density diagnostic from EUVE Spectrometers observations.
Landini, M.; Monsignori Fossi, B. C.
EXOSAT and IUE observations of the active star AU Mic are used to develop a model of the differential emission measure distribution (DEM) versus temperature. The signals detectable by the Extreme UltraViolet Explorer Spectrometers are predicted. The computation indicates the presence of several highly ionized iron lines in the EUV spectral region.…
Identification of the 1600A feature in Lambda Bootis stars
Koester, D.; Allard, N. F.; Holweger, H.
The nature of the absoprtion feature near 1600A in λ Bootis stars, which is one of the strongest features in these objects, is a longstanding puzzle. In this study we demonstrate that it is caused by quasimolecular absorption leading to a satellite in the Lyman α profile due to perturbations by neutral hydrogen. This feature has also been observed…
Non-LTE spectral analyses of Wolf-Rayer stars : the nitrogen spectrum of the WN6 prototype HD 192163 (WR 136).
Hamann, W. -R.; Koesterke, L.; Wessolowski, U.
Non-Local Thermodynamic Equilibrium (LTE) model calculations for Wolf-Rayet spectra of the nitrogen sequence (WN) are presented, accounting for a complex nitrogen model atom. A detailed fit to the observed spectrum of WR 136 alias HD 192163 (subtype WN6) is performed, providing an observational test of the 'standard model' which implies the ideali…