2006/10/18 by Subhanjoy Mohanty, Ray Jayawardhana, N. Huélamo +3 · 6 citations
Chemistry · Physics and Astronomy · #Astrophysics and Star Formation Studies #Spectroscopy and Laser Applications #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/510877
published as Astrophys.J.657:1064-1091,2007 · Accepted by The Astrophysical Journal, 43 pages text + 16 figs + 1 table
arxiv created 2006/10/18 · openalex publication_date 2007/03/06 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
We present J-band imaging and H+K-band low-resolution spectroscopy of 2MASS1207-3932 AB, obtained with VLT NACO. For the putative planetary mass secondary, we find J = 20.0+/-0.2 mag. The HK spectra of both components imply low gravity, and a dusty atmosphere for the secondary. Comparisons to synthetic spectra yield TeffA ~ 2550+/-150K, and TeffB ~ 1600+/-100K, consistent with their late-M and mid-to-late L types. For these Teff, and an age of 5-10 Myrs, evolutionary models imply MA ~ 24+/-6 MJup and MB ~ 8+/-2 MJup. Independent comparisons of these models to the observed colors, spanning ~I to L', also yield the same masses and temperatures. Our primary mass agrees with other recent analyses; however, our secondary mass, while still in the planetary regime, is 2-3 times larger than claimed previously. This discrepancy can be traced to the luminosities: while the absolute photometry and Mbol of the primary agree with theoretical predictions, the secondary is ~ 2.5+/-0.5 mag fainter than expected in all bands from I to L' and in Mbol. This accounts for the much lower secondary mass (and temperature) derived earlier. We argue that this effect is highly unlikely to result from a variety of model-related problems, and is instead real. This conclusion is bolstered by the absence of any luminosity problems in either the primary, or in AB Pic B which we also analyse. We therefore suggest grey extinction in 2M1207B, due to occlusion by an edge-on circum-secondary disk. This is consistent with the observed properties of edge-on disks around T Tauri stars, and with the known presence of a high-inclination evolved disk around the primary. Finally, the system's implied mass ratio of ~0.3 suggests a binary-like formation scenario. (abridged)