Spectroscopic and photometric observations in Bochum 10 and 11⋆

Abstract

Bochum 10. C1040–588, is a small loose cluster of OB stars with 21 probable members, including 15 OB stars of which 11 are classified O9.5–B2 and another B9 Iab; further members are unlikely. Bochum 11, C1045–598, is a small open cluster with 15 known members, of which seven are classified O8–B2. We present new photometry for 16 members and 18 non-members, and MK spectra for 19 members and nine non-members. The clusters have the following properties, based on statistical Zero-Age Main Sequence (ZAMS) fitting and spectroscopic parallaxes: Bochum 10 has marginally non-uniform extinction (SE = 0.047), and Bochum 11 non-uniform extinction (sE = 0.118). Both have a probable blue supergiant member, and cluster ages of about 7 million yr and less than 3 million yr respectively. Bochum 11 has probable pre-main-sequence members, one possibly on a Hayashi contraction track, whereas Bochum 10 probably has no such members.