Herschel/PACS view of disks around low-mass stars and brown dwarfs in the TW Hya association

TL;DR

This study uses Herschel/PACS observations combined with radiative transfer modeling to analyze disks around low-mass stars and brown dwarfs in the TW Hya association, revealing their flatter structure and potential mass scaling with host stars.

Contribution

First detailed analysis of disk properties around low-mass stars and brown dwarfs using Herschel data and advanced modeling techniques.

Findings

Disks are generally flatter than those around higher-mass stars.

Disk mass extends below values typical for T Tauri stars.

Strong correlation between far-IR fluxes and stellar effective temperatures.

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 $70\,\mu{\rm{m}}$ and $100\,\mu{\rm{m}}$ and three targets at $160\,\mu{\rm{m}}$. Our observations, combined with previous photometry from 2MASS, WISE, and SCUBA-2, enabled us to construct 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 modelling 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., $M_{\rm{disk}} \propto M_{\star}$) observed mainly in low-mass stars may extend down to the brown dwarf regime.