Mid-IR spectroscopy of T Tauri stars in Chamealeon I evidence for processed dust at the ear.pdf

a r X i v : a s t r o - p h / 0 3 0 9 6 9 7 v 1 2 5 S e p 2 0 0 3 Astronomy Astrophysics manuscript no. cha˙arxiv February 5, 2008 (DOI: will be inserted by hand later) Mid-IR spectroscopy of T Tauri stars in Chamealeon I: evidence for processed dust at the earliest stages G. Meeus1, M. Sterzik2, J. Bouwman3, and A. Natta4,? 1 Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam e-mail: gwendolyn@aip.de 2 European Southern Observatory, Casilla 19001, Santiago 19, Chile e-mail: msterzik@ 3 CEA, DSM, DAPNIA, Service d’Astrophysique, CE Saclay, 91191 Gif-sur-Yvette Cedex, France e-mail: bjeroen@discovery.saclay.cea.fr 4 Osservatorio Astrofisico di Arcetri, INAF, Largo E. Fermi 5, 50125 Firenze, Italy e-mail: natta@arcetri.astro.it Received ...; accepted ... Abstract. We present mid-IR spectroscopy of three T Tauri stars in the young Chamealeon I dark cloud obtained with TIMMI2 on the ESO 3.6m telescope. In these three stars, the silicate emission band at 9.7 μm is prominent. We model it with a mixture of amorphous olivine grains of different size, crystalline silicates and silica. The fractional mass of these various components change widely from star to star. While the spectrum of CR Cha is dominated by small amorphous silicates, in VW Cha (and in a lesser degree in Glass I), there is clear evidence of a large amount of processed dust in the form of crystalline silicates and large amorphous grains. This is the first time that processed dust has been detetected in very young T Tauri stars (～ 1 Myr). Key words. circumstellar matter - stars: pre-main sequence; planetary systems: protoplanetary discs; individual: CR Cha, Glass I, VW Cha - infrared: stars 1. Introduction Most studies of the dust composition in young stellar ob- jects have concentrated on Herbig Ae/Be stars (HAEBEs), as they are brighter than solar-mass T Tauri stars (TTS). Silicate emission at 10 μm has been detected in several TTS (Cohen Witteborn 1985; Hanner et al. 1998), b