New members of the Galactic OB association Bochum 7

CORTI MARIELA,; BOSCH GUILLERMO,; NIEMELA VIRPI

Ouro Preto, Brasil

Workshop; Open Issues in Local Star Formation and Early Stellar Evolution; 2003

The existence of the young stellar group Bochum7 (l = 265deg, b = -2deg)was indicated by Moffat & Vogt (1975, A&AS 20, 85). They suggested that several OB stars from the LSS catalog around the WR 12 may be an OB association at 5.8kpc. Young open clusters and OB associations are very important objects for understanding the underlying star formation processes as well as studying the spiral structure of the Galaxy.In this way, Bochum7 could give some information on the spiralstructure of the outer region. Lundstrom & Stenholm (1984,A&AS 58, 163) proposed that Bo7 is an OB association of ~30 pc of size. Sung et al. (1999, JKAS 32, 109) suggested that the stars associated with Bo7 are only a local concentration in the density of young stars belonging to the VelOB3 association.We analyzed UBVR and Halpha CCD photometric data searchingother probable members of the ``Association´´ and selected more than 100 stars brighter than V = 15 with colours belonging to the early stars.The spectra of these stars were obtained at CASLEO, Argentina,with the 2.15m telescope and the REOSC and Boller & Chivens spectrographs.For the determination of spectral types of each probable memberof the association, we employed the Walborn & Fitzpatrick criteria(1990, PASP, 102, 379) and found 27 OB stars with 0.1 < E(B-V) < 0.5 magand distance d = 3 +/- 1 kpc and 42 OB stars with E(B-V) > 0.5 magand distance d = 6 +/- kpc.Working with the stars of the LSS catalog, proposed members ofthe association, we find that LSS1144, LSS1147, LSS1131, LSS1146 andLSS1135 have variable radial velocity being LSS1135 a single-lined O-type binary, which we classify as an O6.5V((f)) system with baricentral velocity of 70 km/s. From these data we derive a spectroscopic and kinematical distance of 5.0kpc for Bo7 (Corti et al., in prep.). The existence of the young stellar group Bochum7 (l = 265°, b = --2°) was indicated by Moffat & Vogt (1975, A&AS 20, 85).They suggested that several OB stars from the LSS cataloge around the WR 12 may be an OB association at 5.8kpc.Young open clusters and OB associations are very important objects for understanding the underlying star formation processes  as well as studying the spiral structure of the Galaxy. In this way, Bochum7 could give some information on the spiral structure of the outer region. Lundstrom & Stenholm (1984, A&AS 58, 163) proposed that Bo7 is an OB association of 30 pc of size. Sung et al. (1999, JKAS 32, 109)  suggested that the stars associated with Bo7 are only a localare only a local concentration  in the density of young stars belonging to the VelOB3 association. We analyzed UBVR and Há CCD photometric data searching other probable members of the “Association´´ and selected more than 100 stars brighter than V = 15 with colours belonging to the early stars. The spectra of these stars were obtained at CASLEO, Argentina, with the 2.15m telescope and the REOSC and Boller & Chivens spectrographs. For the determination of spectral types of each probable member of the association, we employed the Walborn & Fitzpatrick criteria (1990, PASP, 102, 379) and found 27 OB stars with 0.1 < E(B-V) < 0.5 mag and distance d = 3 ± 1 kpc and 42 OB stars with E(B-V) > 0.5 mag and distance d = 6 ± 2 kpc. Working with the stars of the LSS catalog, proposed members of the association, we find that LS1144, LS1147, LS1131, LS1146 and LS1135 have variable radial velocity being LS1135 a single-lined O-type binary,  which we classify as an O6.5V((f)) system with baricentral velocity of 70km/seg. From these data we derive a spectroscopic and kinematical distance of 5.0kpc for Bo7 (Corti et al., 2003, A&A  405, 571) )