The low-mass stellar population in the young cluster Tr 37

Disk evolution, accretion, and environment^{⋆,⋆⋆,⋆⋆⋆,⋆⋆⋆⋆}

¹ Departamento de Física TeóricaFacultad de Ciencias, Universidad Autónoma de Madrid, 28049 Cantoblanco, Madrid, Spain
e-mail: aurora.sicilia@uam.es
² Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721-0065, USA
³ Astronomical Observatory, Ural Federal University, Lenin Avenue 51, 620000 Ekaterinburg, Russia
⁴ Department of Astronomy & Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University Park PA 16802, USA
⁵ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany

Received: 9 May 2013
Accepted: 30 July 2013

Abstract

Aims. We present a study of accretion and protoplanetary disks around M-type stars in the 4 Myr-old cluster Tr 37. With a well-studied solar-type population, Tr 37 is a benchmark for disk evolution.

Methods. We used low-resolution spectroscopy to identify and classify 141 members (78 new ones) and 64 probable members, mostly M-type stars. Hα emission provides information about accretion. Optical, 2MASS, Spitzer, and WISE data are used to trace the spectral energy distributions (SEDs) and search for disks. We construct radiative transfer models to explore the structures of full-disks, pre-transition, transition, and dust-depleted disks.

Results. Including the new members and the known solar-type stars, we confirm that a substantial fraction (~2/5) of disks show signs of evolution, either as radial dust evolution (transition/pre-transition disks) or as a more global evolution (with low small-dust masses, dust settling, and weak/absent accretion signatures). Accretion is strongly dependent on the SED type. About half of the transition objects are consistent with no accretion, and dust-depleted disks have weak (or undetectable) accretion signatures, especially among M-type stars.

Conclusions. The analysis of accretion and disk structure suggests a parallel evolution of dust and gas. We find several distinct classes of evolved disks, based on SED type and accretion status, pointing to different disk dispersal mechanisms and probably different evolutionary paths. Dust depletion and opening of inner holes appear to be independent processes: most transition disks are not dust-depleted, and most dust-depleted disks do not require inner holes. The differences in disk structure between M-type and solar-type stars in Tr 37 (4 Myr old) are not as remarkable as in the young, sparse, Coronet cluster (1−2 Myr old), suggesting that other factors, like the environment/interactions in each cluster, are likely to play an important role in the disk evolution and dispersal. Finally, we also find some evidence of clumpy star formation or mini-clusters within Tr 37.