Search Publications
The solar neighbourhood HR diagram as a quantitative test for evolutionary time scales
Schroeder, K. -P.
The HIPPARCOS parallaxes have provided us with a precise HR diagram (HRD) of the solar neighbourhood, complete within certain limits. The scope of this work is a study of the stellar population densities in characteristic regions of the HRD to test stellar evolutionary time scales. We examine two HRDs (M_v <= 4.0), both based on the single-star…
Discovery of a new 170 S X-ray pulsar 1SAX J1324.4-6200
Parmar, A. N.; Mineo, T.; Angelini, L. +2 more
We report the discovery with BeppoSAX of a new 170.84 +/- 0.04 s X-ray pulsar, XB 1323-619b, found serendipitously in the field of the X-ray binary XB 1323-619 in 1997 August. The source and periodicity are also detected in archival ASCA data taken in 1994. The X-ray spectrum is modeled by a power-law with a photon index of 1.0 +/- 0.4 and absorpt…
Analyzing short-term X-ray variability of Cygnus X-1 with Linear State Space Models
Pottschmidt, Katja; Wilms, Joern; Koenig, Michael +1 more
Cyg X-1 exhibits irregular X-ray variability on all measured timescales. The usually applied shot noise models describe the typical short-term behavior of this source by superposition of randomly occuring shots with a distribution of shot durations. We have reanalyzed EXOSAT ME observations of Cyg X-1\ using the more general Linear State Space Mod…
A comparison of the fast timing behaviour of 4U 1705-44 to that of 4U 1608-52 and Cygnus X-1
van der Klis, M.; Berger, M.
We studied the fast timing behaviour of the atoll source \leavevmode4U 1705-44 using the entire \mboxEXOSAT dataset, four observations covering a total of 230 000 seconds of 1-20 keV spectral and timing data. In one of the observations, \leavevmode4U 1705-44 was in a low intensity ``island'' state and had an unusually hard spectrum. The fast timin…
The acoustic cut-off frequency of roAp stars
Provost, J.; Morel, P.; Weiss, W. W. +2 more
Some of the rapidly oscillating (roAp) stars, have frequencies which are larger than the acoustic cut-off frequency determined from published stellar models which usually assume a grey atmosphere. As the cut-off frequency depends on the T(tau ) relation, we have computed models and adiabatic frequencies for pulsating Ap stars with more realistic a…
The symbiotic system AG Dra: an unexpected photometric period
Bastian, U.
A photometric period of about 380 days is found in 6810 visual magnitude estimates of AG Dra. This is unexpected, since the orbital period of the system is about 552 days. The period is confirmed by Hipparcos photometry. The new periodicity provides an additional constraint on physical models for AG Dra. Detailed observations before the end of the…
ISO Detection of CO(+) toward the protostar IRAS 16293-2422
White, G. J.; Ceccarelli, C.; Caux, E. +4 more
In this letter we report the detection of eight high-N rotational transitions of CO(+) towards a low mass protostar, IRAS 16293-2422. The source was observed with the Long Wavelength Spectrometer on board the Infrared Space Observatory. This is the first time that CO(+) has been detected in a low luminosity source and the first time that high-N li…
Kinematics of the local universe. VI. B-band Tully-Fisher relation and mean surface brightness
Theureau, G.
Continuing our study of the type dependence of the TF relation, we present a new attempt to reduce the scatter of that relation by using the observed mean surface brightness Sigma of galaxies. It is shown that the zero-point of the relation is a continuous function of Sigma , well described by a third or fourth degree polynome. Taking this effect …
A test of B-type star Hβ photometric distances via the HIPPARCOS parallaxes
Knude, J.; Kaltcheva, N.
We test the photometric uvbybeta distances for B III, IV and V type stars, with an emphasis on the effect of rotation on the M_V determination. From the M_V(uvbybeta ) calibration of Balona & Shobbrook (1984), we have derived the absolute visual magnitudes for 176 stars with v sin (i) measurements and have compared them to M_V values derived v…
Mid-IR mapping of the region of N 4 in the Large Magellanic Cloud with ISOCAM
Boulanger, F.; Heydari-Malayeri, M.; Sauvage, M. +9 more
We present images of the N 4 region in the Large Magellanic Cloud obtained with ISOCAM on board ISO through broad band filters centered at 6.75 and 15 mu m. Far from the three H i I regions contained in the map, the emission at both wavelengths is due to the Unidentified Infrared Bands and associated continuum and originates in the external layers…