The Search for Low-mass Companions of B Stars in the Carina Nebula Cluster Trumpler 16

Nancy Remage Evans, Kathleen DeGioia-Eastwood, Marc Gagne, Leisa Townsley, Patrick Broos, Scott Wolk, Yael Naze, Michael Corcoran, Lida Oskinova, Anthony F. J. Moffat, Junfeng Wang, Nolan R. Walborn

Smith. Astroph. Observ. and co

We have developed lists of likely B3--A0 stars (called "late B" stars) in the young cluster Trumpler 16. The following criteria were used: location within 3' of Eta Car, an appropriate V and B-V combination, and proper motion (where available). Color and magnitude cuts have been made assuming an E(B-V) =0.55 mag +/- 0.1, which is a good approximation close to the center of Trumpler 16. These lists have been cross-correlated with X-ray sources found in the Chandra Carina Complex Project (CCCP). Previous studies have shown that only very rarely (if at all) do late main sequence B stars produce X-rays. We present evidence that the X-ray detected sources are binaries with low-mass companions, since stars less massive than 1.4 Msun are strong X-ray sources at the age of the cluster. Both the median X-ray energies and X-ray luminosities of these sources are in good agreement with values for typical low-mass coronal X-ray sources. We find that 39% of the late B stars based on a list with proper motions have low-mass companions. Similarly, 32% of a sample without proper motions have low-mass companions. We discuss the X-ray detection completeness. These results on low-mass companions of intermediate mass stars are complementary to spectroscopic and interferometric results, and probe new parameter space of low mass companions at all separations. They do not support a steeply rising distribution of mass ratios to low masses for intermediate-mass (5 Msun) primaries, such as would be found by random pairing from the Initial Mass Function.

Reference: Accepted for the ApJS Special Issue on the Chandra Carina Complex Project (CCCP)
Status: Manuscript has been accepted


Comments: ArXiV:1103.1344 ; 24 pages, 5 figures. All 16 CCCP Special Issue papers are available at the above http URL through 2011 at least