Search Publications
The comptonized X-ray source X 1724-308 in the globular cluster Terzan 2
Stella, L.; Parmar, A. N.; Guainazzi, M. +3 more
We report on the BeppoSAX observation of the X-ray source X 1724-308 in the globular cluster Terzan 2. The broadband spectrum can be described as the superposition of a power-law with photon spectral index Gamma =~ 1.6-1.9 and a thermal component with typical temperature kT ~ 1 keV. X 1724-308 is detected in the PDS up to 150 keV with a S/N ratio …
The blue-bump of 3C 273
Paltani, S.; Walter, R.; Courvoisier, T. J. -L.
We present optical and ultraviolet observations of 3C 273 covering the whole life of the IUE satellite. We analyze the variability properties of the light curves, and find that two variable components, written V_\nuAA\ and S_\nuBB\ respectively, must contribute to the S_\nuB\ emission in this object. The V_\nuAA\ component produces most of the var…
Spectral analysis of O(He)-type post-AGB stars
Rauch, T.; Dreizler, S.; Wolff, B.
We present an analysis of two recently discovered, very hot hydrogen-deficient post-AGB stars of spectral type O(He), namely HS 1522+6615 and HS 2209+8229, by means of state-of-the-art NLTE model atmospheres based on new optical, UV, and X-ray observations. In the spectra of HS 1522+6615 we discovered a variability of the \Ionw{O}{6}{5290} line co…
ISOPHOT boosts dust masses in spiral galaxies
Siebenmorgen, R.; Chini, R.; Zota, V. +1 more
We report photometry with ISO between 60 and 200 -um of six galaxies. Three of them are active and the extension of their spectra beyond the IRAS bands up to 200 -um confirms our previous conception that most of the dust there is warm and has a fairly uniform temperature of phantom {0}im30K. In the other three galaxies which are inactive, we detec…
The LMC distance modulus from HIPPARCOS RR Lyrae and classical Cepheid data
Luri, X.; Figueras, F.; Torra, J. +2 more
The LM method \cite{luri96}, designed to exploit the Hipparcos data to obtain luminosity calibrations, is applied to derive luminosity calibrations for RR Lyrae and classical Cepheids. From these calibrations the distance to the Large Magellanic Cloud (LMC) is estimated. The distance moduli provided by the two calibrations are in good agreement, g…
The fine structure of the Pleiades luminosity function and pre-main sequence evolution
Meusinger, H.; Piskunov, A. E.; Schilbach, E. +2 more
The luminosity function (LF) of the Pleiades cluster stars was constructed for the study of the LF fine structure related to pre-MS stellar evolution. Theoretical luminosity functions based on present-day pre-MS and MS stellar models were constructed and compared with observations. We tested both power- and log-normal laws describing the cluster s…
Alfven wave transmission and particle acceleration in parallel shock waves
Vainio, R.; Schlickeiser, R.
We study Alfven wave transmission through parallel shocks. First, the paper corrects for mistakes made in a previous study by Campeanu & Schlickeiser on the same subject. It is shown, contrary to CS, that first-order Fermi acceleration by multiple shock crossings is generally more effective than stochastic acceleration in the downstream region…
The interstellar extinction in the solar neighbourhood. I. Statistical approach
Egret, D.; Vergely, J. -L.; Koeppen, J. +1 more
Assuming some specific distribution of the interstellar clouds, we interpret the projected stellar extinction in terms of mean extinction by cloud as well as cloud density on the line of sight. Individual stellar extinctions are derived from Stroemgren photometry and from accurate distances based on Hipparcos parallaxes. Extinction profiles as a f…
The discovery of new gamma Doradus stars from the HIPPARCOS mission
Eyer, L.; Aerts, C.; Kestens, E.
We present a classification of 39 new variable stars with spectral type between A2 and F8 discovered by Hipparcos with the aim to find new gamma Doradus stars. We have used a multivariate classification scheme and report the discovery of 14 new gamma Doradus variables among this unbiased sample. Our results point out the biased nature towards hot …
Intraday variability in X-ray selected BL Lacertae objects
Wagner, S. J.; Heidt, J.
We present a study of the intraday variability behaviour of two samples of X-ray selected BL Lac objects, the EMSS and EXOSAT samples consisting of 22 and 11 sources, respectively. In both samples we were able to detect intraday variability in less than 40% of the sources only. The duty cycle (the fraction of time, when a BL Lac object is variable…