Collinder 121

In the paper Burningham et al (2003) we describe our use of XMM-Newton (Table 2) and ROSAT (Table 3) data, along with SuperCosmos proper motions to identify the pre-main sequence (Table 4) in a VI catalogue of Cr 121 produced using these algorithms (Table 1). Those stars that were de-selected on the basis of proper motions are given in Table 5. By fitting isochrones of D'Antona and Mazzitelli (1997) to the PMS, and considering the density of PMS stars, their age spread and the higher mass members of groups along this sightline, we confirm the results of Eggen (1981) and Kaltcheva (2000) that Cr 121 is a compact, young cluster at a distance of about 1 kpc. We argue that the group identified by de Zeeuw et al (1999) as Cr 121 at a distance of 592 pc should be called CMa OB2 (after Eggen (1981)). Note that Table 2 and Table 3 are not in cluster format. See the headers of the tables for a description. This paper also formed part of Ben's thesis.