Substellar companion to CT Cha

http://arxiv.org/abs/0809.2812
Direct evidence of a sub-stellar companion around CT Cha

Abstrat wrote:

In our ongoing search for close and faint companions around T Tauri stars, we found a very faint (Ks=14.9mag, Ks_0=14.4mag) object, just ~2.67" northwest of the Chamaeleon star-forming region member CT Cha corresponding to a projected separation of ~440AU at 165+/-30 pc. We show that CT Cha A and this faint object form a common proper motion pair from data of the VLT Adaptive Optics (AO) instrument NACO taken in February 2006 and March 2007 and that the companion is by >=4 sigma significance not a stationary background object. Our AO integral field spectroscopy with SINFONI in J, and H+K bands yields a temperature of 2600+/-250K for the companion and an optical extinction of A_V=5.2+/-0.8mag, when compared to spectra calculated from Drift-Phoenix model atmospheres. We demonstrate the validity of the model fits by comparison to several other well-known young sub-stellar objects. Relative flux calibration of the bands was achieved using photometry from the NACO imaging data. We conclude that the CT Cha companion is a very low-mass member of Chamaeleon and very likely a physical companion to CT Cha, as the probability for a by chance alignment is <=0.01. Due to a prominent Pa-Beta emission in the J-band, accretion is probably still ongoing onto the CT Cha companion. From temperature and luminosity (log(Lbol/Lsun)= -2.68+/-0.21), we derive a radius of R=2.20+0.81-0.60 R_Jup. We find a consistent mass of M=17+/-6 MJup for the CT Cha companion from both its luminosity and temperature when placed on evolutionary tracks. Hence, the CT Cha companion is most likely a wide brown dwarf companion or possibly even a planetary mass object.

Sounds interesting, but I'm a bit confused about parameters.
Companion's temperature seems close to 2700 K (close to an M2-M5 dwarf) and radius of 0.22 Solar radii (=2.2 Jupiter radii). But mass ranging 17-23 times that of Jupiter...

Edasich: it hasn't cooled down yet - CT Chamaeleontis is a T Tauri star, it hasn't even joined the main sequence yet.

The paper gives a temperature of 2600 K. M2-M5 dwarf is roughly 3000-3500 K. The paper states the spectral type is about M8-L0, which fits quite well with the graphs on this page

This one's on EPE's unconfirmed list because association with CT Tau is not yet confirmed.

(Still, it's doing better than CHXR 73B and DH Tau B which aren't on there at all, despite having masses less than 13 Jupiter masses - I guess the brown dwarf verdict has been passed on these two)

New Extinction and Mass Estimates from Optical Photometry of the Very Low Mass Brown Dwarf Companion CT Chamaeleontis B with the Magellan AO System
http://arxiv.org/abs/1501.01396

Quote :

We used the Magellan adaptive optics (MagAO) system and its VisAO CCD camera to image the young low mass brown dwarf companion CT Chamaeleontis B for the first time at visible wavelengths. We detect it at r′, i′, z′, and YS. With our new photometry and Teff  2500 K derived from the shape its K−band spectrum, we find that CT Cha B has AV = 3.4±1.1 mag, and a mass of 14−24 MJ according to the DUSTY evolutionary tracks and its 1 − 5 Myr age. The overluminosity of our r′ detection indicates that the companion has significant H emission and a mass accretion rate  6×10−10M⊙/yr, similar to some substellar companions. Proper motion analysis shows that another point source within 2′′ of CT Cha A is not physical. This paper demonstrates how visible wavelength AO photometry (r′, i′, z′, YS) allows for a better estimate of extinction, luminosity, and mass accretion rate of young substellar companions.