An oral poster presentation Understanding the SEDs of

An oral poster presentation: Understanding the SEDs of HAe. Be stars Joke Meijer University of Amsterdam Roy van Boekel, Michiel Min, Alex de Koter, Carsten Dominik, Kees Dullemond, Rens Waters Ringberg, April 2004

Overview of Talk • • Herbig stars Group I & II classification Aim of this study: what controls source being Group I or II Results and conclusions Ringberg, April 2004

Herbig Ae/Be stars • • More massive analogues of T Tauri stars Class II objects according to Lada classification Large IR excess due to thermal emission of CS dust Sites of on-going planet formation • IR energy distributions can be divided into two groups Ringberg, April 2004

Group I & II classification Based on ISO continua, SED may be represented by: Power-law + black body “flat” mid-IR Power-law strong decline towards far-IR Meeus et al. 2001 Ringberg, April 2004

Physical interpretation Group I & II Ringberg, April 2004

Comparison Group I & II SEDs Ringberg, April 2004

Group I & II in terms of IR colors Ringberg, April 2004 van Boekel et al. 2003

Definition of LNIR and LIR Ringberg, April 2004

Proposed mechanisms leading to (non-)flaring • Geometrically large or small disks – only way for DDN model to explain Group I & II (Dominik et al. 2002) – however, Group II cases observed to have disks much larger than required (Mannings & Sargent 1997) • Disks with puffed-up inner rim and self-shadowing – overal low disk mass, and/or concentrating mass in inner region leads to self-shadowing Group II – implying Group II sources have relatively low sub-mm emission – sub-mm flux may be increased by adding extra mass in form of midplane component of large grains, preserving Group II properties (Dullemond 2003, Dullemond & Dominik 2004) Ringberg, April 2004

Aim of this study • Extended parameter study, following Dullemond & Dominik (2004), to determine what controls Group I & II, studying – – – inclination mass distribution disk size dust composition • First quantitative comparison of models and observations, using color-color diagram Ringberg, April 2004

Passive disk model Dullemond & Dominik 2004 • 2 D axi-symmetric passive disk with prescribed surface density distribution (r) • Iterative procedure to obtain vertical hydrostatic structure, subject to 2 D radiative equilibrium • Dust consists of a homogeneous distribution of silicate & carbon grains, in different sizes, combined into a single opacity • Allows self-consistent treatment of self-shadowing effects Ringberg, April 2004

Investigated parameter space • Central star – Teff = 10, 000 K – R* = 3 Rsun – M* = 2 Msun • Disk – Mdisk = 10 -2. . 10 -4 Msun � r-p, where p = 1. . 2 – Rdisk = 200. . 600 AU Ringberg, April 2004

Effect of inclination Ringberg, April 2004

Effect of disk mass Ringberg, April 2004

Effect of surface density distribution Ringberg, April 2004

Effect of disk size Ringberg, April 2004

Full grid fails to reach Ib sources . . as no 10 micron feature implies low LIR, therefore high LNIR/LIR Ringberg, April 2004

Conclusions • Two order of magnitude change in mass of small grains can in itself explain Group I & II sources • Either (or both) Group II sources have – lower mass (sub-mm flux indicates up to factor 10) – component of large grains (> 1 mm) in which mass is “hidden” • Mass distribution, outer radius & inclination play a less important though non-negligible role • Group Ib sources (i. e. “flat” IR spectrum, no 10 m feature) are not reproduced by models • Current generation of 2 D models give fair match to observed stars in terms of IR colors, but not (yet) to detailed SED. Needed improvements include – more detailed dust composition – non-homogeneous dust distribution (growth & settling) Ringberg, April 2004

The End Ringberg, April 2004