Volume 491, Number 3, December I 2008
|Page(s)||829 - 831|
|Section||Stellar structure and evolution|
|Published online||18 August 2008|
Identification of the TW Hydrae association member 2M1235-39: a tertiary component of the HR 4796 system
Laboratoire d'Astrophysique de Grenoble, Université Joseph Fourier – CNRS, BP 53, 38041 Grenoble Cedex, France e-mail: email@example.com
2 Chester F. Carlson Center for Imaging Science, Rochester Institute of Technology, 54 Lomb Memorial Dr., Rochester, NY 14623, USA
3 Dept. of Physics & Astronomy, University of California, Los Angeles 90095, USA
4 UCLA Center for Astrobiology, University of California, Los Angeles 90095, USA
5 Research School of Astronomy and Astrophysics, The Australian National University, Weston, ACT 2611, Australia
Accepted: 7 August 2008
Aims. 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 Hα 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 Hα 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 Hα 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.
Key words: stars: individual: 2M1235-39 / stars: pre-main sequence / stars: individual: HR 4796
© ESO, 2008
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