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Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| Search for GRB X-ray afterglows in the ROSAT all-sky survey
We describe a search for X-ray afterglows from gamma-ray bursts usingthe ROSAT all-sky survey (RASS) data. If the emission in the soft X-rayband is significantly less beamed than in the gamma-ray band, we expectto detect many afterglows in the RASS. Our search procedure generated 23afterglow candidates, where about 4 detections are predicted. However,follow-up spectroscopy of several counterpart candidates stronglysuggests a flare star origin of the RASS events in many, if not all,cases. Given the small number of events we conclude that the ROSATsurvey data are consistent with comparable beaming angles in the X-rayand gamma-ray bands. This result is perhaps not surprising, given thatthe data constrain the relative beaming fraction only within a few hoursof the burst. However, models predicting a large amount of energyemerging as a nearly isotropic X-ray component of the early aftergloware severely constrained by the ROSAT data. In particular, a so farundetected class of ``dirty fireballs'' and delayed ``rebursts'' areconstrained.
| Photographic light curves and orbits of seven southern eclipsing binaries
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