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

Using photometric and spectroscopic observations of the double-lined early-type eclipsing binary system ALS 1135, a member of the distant OB association Bochum 7, we derived the new physical and orbital parameters of its components. The masses of both components were derived with an accuracy better than 1 per cent, and their radii, with an accuracy better than 3 per cent. Since the primary's mass is equal to about 25M, its radius was subsequently used to derive the age of the system which is equal to 4.3 ± 0.5Myr. The result shows that this 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 Vel OB1, the other six are δ Scuti stars. Of the six δ Scuti stars three might belong to Vel OB1, the other two are likely members of Bochum 7. Given the age of Bochum 7, these two stars are probably pre-main-sequence pulsators. In addition, we provide UBVIC photometry for about 600 stars in the observed field.