Poster Abstract

P.8 Per-Gunnar Valegård (Anton Pannekoek Institute for Astronomy, Amsterdam)

What happened before -- The disks around the precursors of young Herbig Ae/Be stars

The view of the formation of planetary systems in intermediate mass stars is incomplete since most studies focus on the fairly old Herbig Ae/Be stars (5-10 Myr). By identifying the progenitors to the Herbig stars, the Intermediate Mass T-Tauri (IMTT) stars, in literature we seek to bridge the gap between the embedded and Herbig phase of planetary formation.
Using optical photometry in literature and distances determined from Gaia DR2 parallax measurements together with Kurucz stellar model spectra to place the stars in a HR-diagram, together with Siess evolutionary tracks, we identify 1.5-5.0 Msun IMTT stars in literature by deriving their masses and ages. Using Spitzer spectra we classify their disks into Meeus Group I and Group II disks based on their F30/F13.5 spectral index. We examine the 10 μm silicate dust grain emission and identify emission from Polycyclic Aromatic Hydrocarbons. Building a qualitative picture of IMTT star disks and compare this with available spatially resolved images at infrared and at sub-millimeter wavelengths we confirm our classification. Compared to the Herbig stars, IMTT star disks are similar in disk geometries and silicate dust grain population. The spatially resolved data suggest that disk features (gaps, spirals and rings) are already present in the younger IMTT stars. Comparing the timescale of stellar evolution towards the main sequence and current models of protoplanetary disk evolution the similarity between Herbig Ae/Be stars and the IMTT stars points towards that Group I and Group II disks represents two different evolutionary paths for protoplanetary disks.