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

Abstract

We present the results of a multiwavelength 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 μm can be used to derive robust estimates of the disc mass. The median disc mass is 0.005 M⊙ for a sample of 28 Class IIs and 0.006 M⊙ for 6 transition discs (TDs). The fraction of objects in Chamaeleon-I with at least the ‘minimum mass solar nebula’ is 2–7 per cent. This is consistent with previously published results for Taurus, IC348 and ρ 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 from 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.