Query : 2010A&A...521A..24J

2010A&A...521A..24J - Astronomy and Astrophysics, volume 521, A24-24 (2010/10-1)

Improved radial velocity orbit of the young binary brown dwarf candidate Cha Hα 8.


Abstract (from CDS):

The very young brown dwarf candidate ChaHα8 was recently discovered to have a close (∼1AU) companion by means of radial velocity monitoring. We present additional radial velocity data obtained with UVES/VLT between 2007 and 2010, which significantly improve the orbit determination of the system. The combined data set spans ten years of radial velocity monitoring for ChaHα8. A Kepler fit to the data yields an orbital period of 5.2 years, an eccentricity of e=0.59, and a radial velocity semi-amplitude of 2.4km/s. A companion mass M2sini (which is a lower limit due to the unknown orbital inclination i) of 25±7MJup and of 31±8MJup is derived when using model-dependent mass estimates for the primary of 0.07M and 0.10M, respectively. Assuming random orientation of orbits in space, we find a very high probability that the companion of ChaHα8 is of substellar nature: With a greater than 50% probability (i≥60°), the companion mass is between 30 and 35MJup and the mass ratio M2/M1 smaller than 0.4; with a greater than 87% probability (i≥30°) the companion mass is between 30 and 69MJup and the mass ratio smaller than 0.7. The absence of any evidence of the companion in the cross-correlation function together with the size of the radial velocity amplitude also indicate a mass ratio of at most 0.7, and likely smaller. Furthermore, the new data exclude the possibility that the companion has a mass in the planetary regime (≤13MJup). We show that the companion contributes significantly to the total luminosity of the system: model-dependent estimates provide a minimum for the luminosity ratio L2/L1 of 0.2. ChaHα8 is the fourth known spectroscopic brown dwarf or very low-mass stellar binary with determined orbital parameters, and the second known very young one. With an age of only about 3Myr, it is of particular interest to very low-mass formation and evolution theories. In contrast to most other spectroscopic binaries, it has a relatively long orbital period and it might be possible to determine the astrometric orbit of the primary and, thus, the orbital inclination.

Abstract Copyright:

Journal keyword(s): techniques: radial velocities - binaries: spectroscopic - stars: individual: Cha Hα 8 - stars: pre-main sequence - stars: low-mass - planets and satellites: detection

Simbad objects: 8

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Number of rows : 8
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 2MASS J03202839-0446358 LM* 03 20 28.3630482681 -04 46 36.396685568           M8.5+T5 44 0
2 Cl Melotte 22 OpC 03 46 24.2 +24 06 50           ~ 3354 0
3 V* UZ Tau B TT* 04 32 42.8118779016 +25 52 31.198173600   14.07 12.72 13.35   M1/3Ve 149 0
4 V* V2384 Ori EB* 05 35 21.8473218600 -05 46 08.571352260       19.21 17.28 M7 97 1
5 LSPM J0746+2000 BD* 07 46 42.50553 +20 00 31.9757       17.9 15.034 L0+L1.5 183 1
6 NAME Cha 1 MoC 11 06 48 -77 18.0           ~ 1132 1
7 [NC98] Cha HA 8 SB* 11 07 46.0912894776 -77 40 08.918309388   22.2 20.1   15.61 ~ 43 1
8 BD+16 2708B SB* 14 54 29.4185719182 +16 06 08.616294953           M8.5 136 0

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