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
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.
Fetch Pdf-File (apjs_194_1_13.pdf, 505kB)