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Photometric Variability of the Gravitational Lens 0142-100 (UM 673)
We present the results of a photometric CCD monitoring of thegravitational lens system UM 673 that took place from 1995 to 2000. Intotal, the doubly imaged quasar (QSO) was observed in the R band during29 photometric nights, using optical telescopes with dimensions in therange 0.6-1.3 m. We detected a significant variability in the totallight of the UM 673 system, that is, in the light of the two QSO imagesplus the lensing galaxy. With respect to the magnitude of thegravitational lens system at its discovery, in 1986, UM 673 was 0.3 magbrighter. Furthermore, our 1996 December measurements show that between1995 November and 1997 October the system became even brighter, reachinga magnitude difference of 0.5 mag with respect to its discovery value.We also present R magnitudes and V-R colors of seven field starssituated in the vicinity of the lens, based on a 3.5 month monitoringduring the year 2000. Based on observations made with (1) the 60 cmBochum and the ESO 90 cm Dutch telescopes, at La Silla, Chile, (2) the1.2 m telescope at Kryonerion Observatory, Greece, (3) the 1.3 mtelescope at Skinakas Observatory, Crete, Greece, and (4) the EuropeanSpace Agency OGS telescope operated on the island of Tenerife by theInstituto de Astrofísica de Canarias in the Spanish Observatoriodel Teide of the Instituto de Astrofísica de Canarias.
| A homogeneous catalog of new UBV and H-beta photometry of B- and A-type stars in and around the Scorpius-Centaurus OB association
B- and A-type stars in and near the Sco-Cen OB association areinvestigated with UBV and H-beta photometry to acquire data relevant tothe luminosity function of Sco-Cen. The measurements generally consistof two 10-s integrations of U, B, V, (W, N) filters, and theobservations are corrected iteratively for atmospheric extinction andinstrumental response. The data presented give the mean V magnitude,mean B-V, mean U-B, and the estimated uncertainties for these values.The catalog provides a homogeneous catalog of data for a large fieldwith stellar objects delineating membership to the association Sco-Cenand that affect the luminosity function of the aggregate.
| The distance and structure of the Coalsack. I - Photometric data
The results of UBV and H-beta photometry for 284 stars of spectral typesB to F located in the area of the dark cloud Coalsack are presented.Most of the present stars are brighter than 10.0 mag and are classifiedin the MK system of Houk and Cowley (1975). For each star, the bestvalues for the extinction and distance modulus are provided, withtypical estimated errors of + or - 0.08 mag for the extinction and + or- 0.32 mag for the distance modulus. Possible misclassifications andspectral peculiarities are noted for several of the stars.
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