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uvby - β Photoelectric Photometry of the Open Cluster α Per
Absolute photoelectric photometry of stars in the direction of the OpenCluster α Per has been secured and is presented along with ananalysis reinforced with all the available data in Strömgrenuvby-β photometry compiled from the literature. Cluster membershipis analyzed and the physical characteristics of the stars have beendeduced. The membership determined in this paper is compared with thatof proper motion studies and Hipparcos.
| I. UBV photometry of selected members of the Pleiades and Alpha Persei clusters in 1999
The rotational brightness variations in magnetically active stars aredue to the combined light contribution of cool spots and bright faculaeon the stellar photosphere. The amplitude of the rotational brightnessvariations can be used to probe the dependence of the amount ofphotospheric magnetic fields associated to such inhomogeneities onglobal stellar parameters such as the rotation rate. However, the upperenvelope of the amplitude values must be considered, since therotational modulation amplitude represents a lower limit of the spotsand faculae coverage, being their visibility modulation reduced byseveral factors. In order to determine accurately the maximum amplitudeupper envelope and its dependence on global stellar parameters a programof photometric monitoring of ultra fast rotating active members of thePleiades and Alpha Persei star clusters was undertaken in the fall of1999. Light curves and period determinations of 21 target stars arepresented as result from the first observing season. The newlydetermined values of amplitudes of the brightness variations versusrotation period have values as expected based on previous results.
| Radial velocity measurements. II - Ground-based observations of the program stars for the HIPPARCOS satellite
New radial velocities for 446 stars of magnitude 9.0 or brighter in 1616-sq-deg fields of the Northern Hemisphere are determined by automaticPDS measurement of 80-A/mm-dispersion spectra obtained at theObservatoire de Haute Provence using a 17-cm-diameter objective prism.The fields were selected to provide data for the input catalog of theESA Hipparcos astrometric satellite. The measurement techniques andprecision are discussed, and the results are presented in extensivetables and graphs.
| Eigenbewegungen in der Umgebung von α Persei
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