SIMBAD references

Several dozen stars are identified as probable previously unrecognized members of the association Vel OB1, including the Vela X-1 binary pulsar system. Based on a variable extinction analysis of 70 stars, the distance and ratio of total to selective absorption of the association are determined to be 1750 pc and 3.70, respectively. Vel OB1 may be significantly larger than previously appreciated, perhaps up to 600 by 300 pc in the sense of longitude by latitude. This physical extent, and the fact that the H-R diagram includes both low-mass evolved yellow supergiants and massive, early-type supergiants, indicates that Vel OB1 is probably not coeval.