The stellar composition of the star formation region CMa R1 -- I. Results from new photometric and spectroscopic classifications

Abstract

A new photometric and spectroscopic survey of the star formation region (SFR) CMa R1 is described. In a sample of 165 stars brighter than 13th mag, 88 stars were found to be probable members of the SFR. They are defined as early‐type stars with E(B−V)0.16 mag, which corresponds to a distance of about 1 kpc. 74 of the probable members are B stars. 19 stars are possibly associated with an IRAS point source. We derive a most probable distance of 1050±150 pc to the association. It appears that about 80 candidate members are pre‐main‐sequence stars with ages lower than 6 million years, while the main sequence extends over 6.0–7.6 mag, which is consistent with star formation starting about 8 million years ago and continuing until at least half a million years ago. Two bright B stars in the association (GU CMa and FZ CMa) seem to be much older and probably do not originate from the same star formation episode. The star formation efficiency appears to increase roughly monotonically with time up to half a million years ago. From our data, we conclude that only a minor fraction of the stars has been created through the scenario suggested by Herbst & Assousa, in which the members of CMa R1 form by compression of ambient material by a supernova shock wave. An extensive search for candidate members with Hα emission did not reveal new Herbig Ae/Be candidates, so that the number of stars in this class seems to be limited to four: Z CMa, LkHα 218, LkHα 220 and possibly HD 53367.

Star formation history of Canis Major R1

“…rectangular area that overlaps the Sh2-296 arc, revealing 88 members of the CMa R1 association (74 B stars, no O star) with ages between 8 and 0.5 Myr, apparently suggesting an extended period of star formation activity that is still ongoing. Shevchenko et al (1999) also point out that two other bright B stars, GU CMa and FZ CMa, seem to be older than the association and may not have been formed in the same star formation episode. Other early B stars associated with Sh2-296 include Z CMa, a double system (Koresko et al 1991;Haas et al 1992) containing a FU Orionis object (Hartmann et al 1989) and a Herbig Be star, with a common age of about 0.3 Myr (van den Ancker et al 2004).…”

“…CMa R1 is an association of bright stars and clusters distributed around and in the vicinity of the long (200 ) arc-shaped ionized reflection nebula Sh2-296 (Sharpless 1959: l = 224.6 • , b = −2 • ), located at a distance d ∼ 1 kpc (Shevchenko et al 1999;Kaltcheva & Hilditch 2000). In the absence of conspicuous exciting early-type stars inside the arc, the source of ionization is still being debated.…”

“…The field-of-view of X-ray observations are indicated for: ROSAT (white lines); XMM-Newton (blue) and Chandra (yellow). The large rectangular white box shows the area covered by the optical survey of OB stars by Shevchenko et al (1999), while the small square box including GU CMa corresponds to the area where Gemini observations of unresolved X-ray sources were carried out. Objects discussed in the text are labelled by their names.…”

“…These clusters were studied by Soares & Bica (2002, 2003, who used JHK data from 2MASS ("The Two Micron All Sky Survey", Skrutskie et al 2006). Based on colour-magnitude diagrams, they estimated ages of 1.5 Myr (NGC2327 and BRC27) and 5-7 Myr (VdB-RN92), spanning the same age range as the sample of Shevchenko et al (1999).…”

Evolution of Emission‐Line Activity in Intermediate‐Mass Young Stars

“…In x 2 of the paper we describe our sample. Spectroscopic observations obtained are presented in Baines et al 2004;(18) Malfait et al 1998;(19) Acke et al 2005;(20) Testi et al 1998;(21) van den Ancker et al 2004;(22) Corcoran & Ray 1998;(23) Miroshnichenko et al 2001b;(24) Alencar et al 2003;(25) Hamaguchi et al 2005;(26) Terranegra et al 1994;(27) van den Ancker et al 1998;(28) Berrilli et al 1992;(29) Perryman et al 1997;(30) Calvet et al 2004;(31) Leinert et al 1997;(32) Kawamura et al 1998;(33) Hernández et al 2005;(34) Herbst & Racine 1976;(35) Herbst et al 1982;(36) Shevchenko et al 1999;(37) Leinert et al 2004;(38) Eisner et al 2004;(39) Shevchenko & Yakubov 1989. x 3. Main results of our study are presented in x 4 and discussed in detail in x 5.…”