Fossil sequential star formation in the CMa R1 regionquestionMark

The CMa R1 region includes the arcshaped ionized nebula S2296, suggested to bean old supernova remnant, as well as several very young (less than 5 Myr)clusters. Based on archival ROSAT observations covering nearly 5 sq. deg. wehave discovered a new, 10Myr old cluster that may be a fossil from a distinct,past starformation episode, suggesting sequential star formation betweensupernova cavities. We propose a mosaic of 5 x 30ks EPIC fields to reveal amixed population from both older and young clusters corresponding respectivelyto a fossil, and to an onging, star formation episode. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]