UBV-IR photometry and optical spectroscopy of the galactic OB association Bochum 7

CORTI MARIELA; BOSCH GUILLERMO; NIEMELA VIRPI

Carilo, Buenos Aires, Argentina.

Workshop; Massive Stars: Fundamental Parameters and Circumstellar Interactions; 2006

The lack of tightly bound and easily identifiable young openclusters leads to the quest for OB associations as tracers ofspiral arms. Massive stars are usually found in groups, and thepresence of a Wolf-Rayet star, WR12 in the catalogue of galacticWR stars (van der Hucht 2001), at alpha = 8:44:47.2,delta = - 45:58:55.5 (J2000.0), triggered the searchfor an surrounding OB association, now knownas Bochum7 (Moffat & Vogt 1975). From UBV imaging of a 30 arcmin field surrounding WR12, obtained atCTIO, Chile, aperture photometry was obtained to select candidatesand optical spectroscopic observations were obtained in CASLEO,Argentina, for over one hundred stars. 63 stars were classified asOB type, including the stars LS1131, 1132, 1135, 1137, 1140, 1144,1146, 1147 already present in the LSS catalogue. The OB stars were used to test the properties of the interstellardust in the line of sight and the relation between the diffuseinterstellar band at 4428A which grows linearly withE(B-V) until 1 mag. Combining our data with 2MASS IRphotometry we could estimate the value of E(V-K) whichenabled us to derive a more accurate value for the totalabsorption in the line of sight and derive spectroscopic distancesfor the stars, the value of mean distance is 4.2kpc and 4.0kpcwith E(B-V) and E(V-K), respectively. With the aid of the CHORIZOS code, the combined spectrophotometricinformation was also used to analyse fundamental stellar parameters(such as Teff) and probe changes in the interstellar mediumbehaviour.