Herschel/PACS view of disks around low-mass stars and brown dwarfs in the TW Hydrae association^⋆,⋆⋆

¹ Purple Mountain Observatory, Chinese Academy of Sciences, 2 West Beijing Road, 210008 Nanjing, PR China
e-mail: yliu@pmo.ac.cn
² Key Laboratory for Radio Astronomy, Chinese Academy of Sciences, 2 West Beijing Road, 210008 Nanjing, PR China
³ Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Haidian Qu, 100871 Beijing, PR China
⁴ Tsinghua University, Shuang Qing Lu 30, Haidian Qu, 100084 Beijing, PR China
⁵ Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Peyton Hall, Princeton, NJ 08544, USA
⁶ Department of Physics and Astronomy, Bucknell University, Lewisburg, PA 17837, USA
⁷ Harvard-Smithsonian Center for Astrophysics, 60 Garden St., MS 78, Cambridge, MA 02138, USA
⁸ Department of Astronomy, The University of Texas at Austin, Austin, TX 78712, USA
⁹ Institute for Astronomy, University of Hawaii at Manoa, 2680 Woodlawn Dr., Honolulu, HI 96822, USA
¹⁰ Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ, 86001, USA
¹¹ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
¹² Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany

Received: 31 July 2014
Accepted: 17 October 2014

Abstract

We conducted Herschel/PACS observations of five very low-mass stars or brown dwarfs located in the TW Hya association with the goal of characterizing the properties of disks in the low stellar mass regime. We detected all five targets at 70 μm and 100 μm and three targets at 160 μm. Our observations, combined with previous photometry from 2MASS, WISE, and SCUBA-2, enabled us to construct spectral energy distributions (SEDs) with extended wavelength coverage. Using sophisticated radiative transfer models, we analyzed the observed SEDs of the five detected objects with a hybrid fitting strategy that combines the model grids and the simulated annealing algorithm and evaluated the constraints on the disk properties via the Bayesian inference method. The modeling suggests that disks around low-mass stars and brown dwarfs are generally flatter than their higher mass counterparts, but the range of disk mass extends to well below the value found in T Tauri stars, and the disk scale heights are comparable in both groups. The inferred disk properties (i.e., disk mass, flaring, and scale height) in the low stellar mass regime are consistent with previous findings from large samples of brown dwarfs and very low-mass stars. We discuss the dependence of disk properties on their host stellar parameters and find a significant correlation between the Herschel far-IR fluxes and the stellar effective temperatures, probably indicating that the scaling between the stellar and disk masses (i.e., M_disk ∝ M_⋆) observed mainly in low-mass stars may extend down to the brown dwarf regime.