MOA-2007-BLG-197: Exploring the brown dwarf desert
Abstract
We present the analysis of MOA-2007-BLG-197Lb, the first brown dwarf companion to a Sun-like star detected through gravitational microlensing. The event was alerted and followed-up photometrically by a network of telescopes from the PLANET, MOA, and uFUN collaborations, and observed at high angular resolution using the NaCo instrument at the VLT. From the modelling of the microlensing light curve, we derived the binary lens separation in Einstein radius units (s~1.13) and a mass ratio of (4.732+/-0.020)x10^{-2}. Annual parallax, lens orbital motion and finite source effects were included in the models. To recover the lens system's physical parameters, we combined the resulting light curve best-fit parameters with (J,H,Ks) magnitudes obtained with VLT NaCo and calibrated using IRSF and 2MASS data. We derived a lens total mass of 0.86+/-0.04 Msun and a lens distance of 4.2+/-0.3 kpc. We find that the companion of MOA-2007-BLG-197L is a brown dwarf of 41+/-2 Mjup observed at a projected separation of 4.3+/-0.1 AU, and orbits a 0.82+/-0.04 Msun G-K dwarf star. We study the statistical properties of this population of brown dwarfs detected by microlensing, transit, radial velocity, and direct imaging (most of these objects orbit solar-type stars), and we performed a two-dimensional, non-parametric probability density distribution fit to the data, which draws a structured brown dwarf landscape. We confirm the existence of a region that is strongly depleted in objects at short periods and intermediate masses (P<30 d, M~30-60 Mjup), but also find an accumulation of objects around P~500 d and M~20 Mjup, as well as another depletion region at long orbital periods (P>500 d) and high masses (M>50 Mjup). While these data provide important clues on mechanisms of brown dwarfs formation, more data are needed to establish their relative importance, in particular as a function of host star mass.
Cite
@article{arxiv.1505.06037,
title = {MOA-2007-BLG-197: Exploring the brown dwarf desert},
author = {C. Ranc and A. Cassan and M. D. Albrow and D. Kubas and I. A. Bond and V. Batista and J. -P. Beaulieu and D. P. Bennett and M. Dominik and Subo Dong and P. Fouqué and A. Gould and J. Greenhill and U. G. Jørgensen and N. Kains and J. Menzies and T. Sumi and E. Bachelet and C. Coutures and S. Dieters and D. Dominis Prester and J. Donatowicz and B. S. Gaudi and C. Han and M. Hundertmark and K. Horne and S. R. Kane and C. -U. Lee and J. -B. Marquette and B. -G. Park and K. R. Pollard and K. C. Sahu and R. Street and Y. Tsapras and J. Wambsganss and A. Williams and M. Zub and F. Abe and A. Fukui and Y. Itow and K. Masuda and Y. Matsubara and Y. Muraki and K. Ohnishi and N. Rattenbury and To. Saito and D. J. Sullivan and W. L. Sweatman and P. J. Tristram and P. C. M. Yock and A. Yonehara},
journal= {arXiv preprint arXiv:1505.06037},
year = {2015}
}
Comments
16 pages, 12 figures