Identification of the TW Hya Association Member 2M1235 −39: a Tertiary Component of the HR 4796 System
This is the pre-print of an article published by EDP Sciences. The final, published version is available here: https://doi.org/10.1051/0004-6361:200810580
Reproduced with permission from Astronomy & Astrophyics, © 2008 ESO
Also archived in: arXiv:0808.2630v1 [astro-ph]
Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works in February 2014.
We seek to determine whether the late-type star 2MASS J12354893−3950245 (2M1235−39) is a member of the TW Hya Association (TWA), a hypothesis suggested by its association with a bright X-ray source detected serendipitously by ROSAT and XMM-Newton and its (∼ 3′) proximity to the well-studied (A+M binary) system HR 4796. Methods. We used optical spectroscopy to establish the Li and H line strengths of 2M1235−39, and determined its proper motion via optical imaging. We also considered its X-ray and near-IR fluxes relative to the M star HR 4796B. Results. The optical spectrum of 2M1235−39 displays strong Li absorption and H emission (equivalent widths of 630 mÅ and −6.7 Å, respectively). Comparison of the spectrum with that of a nearby field star, along with the DENIS catalog IJK magnitudes, indicates the spectral type of 2M1235−39 is M4.5. We measure a proper motion for 2M1235−39 that agrees, within the errors, with that of HR 4796. Conclusions. The Li absorption and H emission line strengths of 2M1235−39, its near-IR and X-ray fluxes, and its proper motion all indicate that 2M1235−39 is a TWA member. Most likely this star is a wide (13,500 AU) separation, low-mass, tertiary component of the HR 4796 system.