The Herschel view of circumstellar discs: a multi-wavelength study of Chamaeleon I

TL;DR

This study uses Herschel multi-wavelength data to analyze circumstellar discs in Chamaeleon I, revealing disc masses, evolutionary trends, and the independence of inner dust clearing from other disc evolution processes.

Contribution

It provides the first robust disc mass estimates from Herschel fluxes and explores the evolutionary relationship between Class II and transition discs in a young star-forming region.

Findings

Median disc mass is around 0.005-0.006 solar masses.

2-7% of objects have discs with at least the minimum mass solar nebula.

No significant difference between Class II and transition discs in far-infrared luminosity or disc mass.

Abstract

We present the results of a multi-wavelength study of circumstellar discs around 44 young stellar objects in the 3 Myr old nearby Chamaeleon I star-forming region. In particular, we explore the far-infrared/submm regime using Herschel fluxes. We show that Herschel fluxes at 160-500$\,\mu$m can be used to derive robust estimates of the disc mass. The median disc mass is 0.005$M_{\odot}$ for a sample of 28 Class IIs and 0.006$M_{\odot}$ for 6 transition disks (TDs). The fraction of objects in Chamaeleon-I with at least the `minimum mass solar nebula' is 2-7%. This is consistent with previously published results for Taurus, IC348, $\rho$ Oph. Diagrams of spectral slopes show the effect of specific evolutionary processes in circumstellar discs. Class II objects show a wide scatter that can be explained by dust settling. We identify a continuous trend from Class II to TDs. Including Herschel fluxes in this type of analysis highlights the diversity of TDs. We find that TDs are not significantly different to Class II discs in terms of far-infrared luminosity, disc mass or degree of dust settling. This indicates that inner dust clearing occurs independently from other evolutionary processes in the discs.