The Planetary Mass Companion 2MASS 1207−3932B: Temperature, Mass, and Evidence for an Edge‐on Disk

We present J-band imaging and H+K-band low-resolution spectroscopy of2MASS1207-3932 AB, obtained with VLT NACO. For the putative planetary masssecondary, we find J = 20.0+/-0.2 mag. The HK spectra of both components implylow gravity, and a dusty atmosphere for the secondary. Comparisons to syntheticspectra yield Teff_A ~ 2550+/-150K, and Teff_B ~ 1600+/-100K, consistent withtheir late-M and mid-to-late L types. For these Teff, and an age of 5-10 Myrs,evolutionary models imply M_A ~ 24+/-6 M_Jup and M_B ~ 8+/-2 M_Jup. Independentcomparisons of these models to the observed colors, spanning ~I to L', alsoyield the same masses and temperatures. Our primary mass agrees with otherrecent analyses; however, our secondary mass, while still in the planetaryregime, is 2-3 times larger than claimed previously. This discrepancy can betraced to the luminosities: while the absolute photometry and Mbol of theprimary agree with theoretical predictions, the secondary is ~ 2.5+/-0.5 magfainter than expected in all bands from I to L' and in Mbol. This accounts forthe much lower secondary mass (and temperature) derived earlier. We argue thatthis effect is highly unlikely to result from a variety of model-relatedproblems, and is instead real. This conclusion is bolstered by the absence ofany luminosity problems in either the primary, or in AB Pic B which we alsoanalyse. We therefore suggest grey extinction in 2M1207B, due to occlusion byan edge-on circum-secondary disk. This is consistent with the observedproperties of edge-on disks around T Tauri stars, and with the known presenceof a high-inclination evolved disk around the primary. Finally, the system'simplied mass ratio of ~0.3 suggests a binary-like formation scenario.(abridged)Comment: Accepted by The Astrophysical Journal, 43 pages text + 16 figs + 1 tabl