Poster Abstracts

Name/Affiliation:  Jonathan Tottle (Imperial College London)

Title:  SED analysis of class II M-type objects in Cha I

The class II stage of a T Tauri star is characterised by the disappearance of the gaseous envelope and the presence of a primordial circumstellar disk. The shape of the SED from observations has strong implications for the geometry, structural evolution and physical conditions within the disk. We model the IR SEDs (using photometry over 2 - 24 microns) of 67 class II M-type objects in Cha I using an MCMC evaluation coupled to the radiative transfer code of Whitney et al. (2003). We find that just over half of the objects appear to host 'standard' accretion disks. These cases explain the majority of class II SEDs, in which we observe both the unobscured star and the strong IR signature of its surrounding disk. Roughly a quarter of the objects appear edge-on, in which the short wavelength emission is suppressed by outer disk occlusion of the central object and inner disk; the outer disk often also occludes accretion signatures arising close to the star in these sources, leading to spuriously low accretion rate estimates. A few objects in our sample show evidence for transition disks with either large inner holes or gradual disk clearing, due to either photo-evaporation from the central star and/or planet formation within the disk. The remaining objects are categorised as 'odd'-looking objects with highly unusual SEDs. A few of these may be explained by errors in the data, but for the majority it is most likely due to either variability or exotic disk geometry. We finish by exploring the relation between estimated accretion rates and disk properties; one expects reduced accretion rates at the end of the class II stage to be accompanied by the gradual flattening of the dusty disk.