Study on Eps Indi Ba and Bb

Epsilon Indi Ba, Bb: a detailed study of the nearest known brown dwarfs
http://arxiv.org/abs/0911.3143

Abstract wrote:

The discovery of epsilon Indi Ba, Bb, a binary brown dwarf system very close to the Sun, makes possible a concerted campaign to characterise the physical parameters of two T dwarfs. Recent observations suggest substellar atmospheric and evolutionary models may be inconsistent with observations, but there have been few conclusive tests to date. We therefore aim to characterise these benchmark brown dwarfs to place constraints on such models. We have obtained high angular resolution optical, near-infrared, and thermal-infrared imaging and medium-resolution (up to R~5000) spectroscopy of epsilon Indi Ba, Bb with the ESO VLT and present VRIzJHKL'M' broad-band photometry and 0.63--5.1 micron spectroscopy of the individual components. Furthermore, we use deep AO-imaging to place upper limits on the (model-dependent) mass of any further system members. We derive luminosities of log L/L_sun = -4.699+/-0.017 and -5.232+/-0.020 for epsilon Indi Ba, Bb, respectively, and using the dynamical system mass and COND03 evolutionary models predict a system age of 3.7--4.3 Gyr, in excess of previous estimates and recent predictions from observations of these brown dwarfs. Moreover, the effective temperatures of 1352--1385 K and 976--1011 K predicted from the COND03 evolutionary models, for epsilon Indi Ba and Bb respectively, are in disagreement with those derived from the comparison of our data with the BT-Settl atmospheric models where we find effective temperatures of 1300--1340 K and 880--940 K, for epsilon Indi Ba and Bb respectively, with surface gravities of log g=5.25 and 5.50. Finally, we show that spectroscopically determined effective temperatures and surface gravities for ultra-cool dwarfs can lead to underestimated masses even where precise luminosity constraints are available.

Very nice work going on there. Also it seems that an update on the orbit and dynamical masses of the system is in preparation. Have to wonder if there are any planets in orbit around either of these brown dwarfs... no massive gas giants down to about 0.8 AU around either.

Update for Epsilon Indi system: dynamical masses measured.

Precise Dynamical Masses of Epsilon Indi Ba and Bb: Evidence of Slowed Cooling at the L/T Transition

Quote :

We report individual dynamical masses of 66.92±0.36MJup and 53.25±0.29MJup for the binary brown dwarfs ε Indi Ba and Bb, measured from long term (≈10 yr) relative orbit monitoring and absolute astrometry monitoring data on the VLT. Relative astrometry with NACO fully constrains the Keplerian orbit of the binary pair, while absolute astrometry with FORS2 measures the system's parallax and mass ratio. We find a parallax consistent with the Hipparcos and Gaia values for ε Indi A, and a mass ratio for ε Indi Ba to Bb precise to better than 0.2%. ε Indi Ba and Bb have spectral types T1-1.5 and T6, respectively. With an age of 3.5+0.8−1.0 Gyr from ε Indi A's activity, these brown dwarfs provide some of the most precise benchmarks for substellar cooling models. Assuming coevality, the very different luminosities of the two brown dwarfs and our moderate mass ratio imply a steep mass-luminosity relationship L∝M5.37±0.08 that can be explained by a slowed cooling rate in the L/T transition, as previously observed for other L/T binaries. Finally, we present a periodogram analysis of the near-infrared photometric data, but find no definitive evidence of periodic signals with a coherent phase.

Now, should these too be included in Extrasolar Planet Encyclopaedia? I think they should but the "binary planet" category should be considered as well, especially after the possible detection of a similar system around DH Tauri, where individual masses are well within Jovian planet domain.