The massive eclipsing system ALS 1135 and variable stars in the field of the distant OB association Bochum 7

Abstract

Using photometric and spectroscopic observations of the double-lined early-type eclipsingbinary system ALS 1135, a member of the distant OB association Bochum 7, we derived thenew physical and orbital parameters of its components. The masses of both components werederived with an accuracy better than 1 per cent, and their radii, with an accuracy better than3 per cent. Since the primary’s mass is equal to about 25M, its radius was subsequentlyused to derive the age of the system which is equal to 4.3 ± 0.5Myr. The result shows thatthis method represents a viable alternative to isochrone fitting.A photometric search of the field of ALS 1135 resulted in the discovery of 17 variable stars,including 7 pulsating ones. One of them is a slowly-pulsating B (SPB) star belonging to VelOB1, the other six are d Scuti stars. Of the six d Scuti stars three might belong to Vel OB1, theother two are likely members of Bochum 7. Given the age of Bochum 7, these two stars areprobably pre-main-sequence pulsators. In addition, we provide UBVIC photometry for about600 stars in the observed field.