Identification of the TW Hya Association Member 2M1235 −39: a Tertiary Component of the HR 4796 System

Joel H. Kastner, Rochester Institute of Technology
B. Zuckerman, University of California, Los Angeles
M. Bessell, The Australian National University

This is the pre-print of an article published by EDP Sciences. The final, published version is available here:

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.