Massive young disks around Herbig Ae stars

摘要

Herbig Ae stars (HAe) are the precursors of Vega-type systems, hence crucial objects in planet formation studies. Thus far, only a few disks associated with HAe stars have been studied using millimetre interferometers. Aims. Our aim is to determine the dust evolution and the lifetime of the disks associated with Herbig Ae stars. Methods. We imaged the continuum emission at ～ 3 mm and ～ 1.3 mm of the Herbig Ae/Be stars BD+61154, RR Tau, VY Mon, and LkHα 198 using the Plateau de Bure Interferometer (PdBI). These stars are in the upper end of the stellar mass range of the Herbig Ae stars (M· ≥ 3 M⊙). Our measurements were used to complete the spectral energy distribution (SED). The modelling of the SED, in particular the FIR-mm part, allows us to determine the masses and dust properties of these disks. Results. We detected the disks associated with BD+61154, RR Tau, and VYMon with disk masses of 0.35 M⊙, 0.05 M⊙, and 0.40 M⊙, respectively. The disk around LkHα 198 was not detected with an upper limit to the disk mass of 0.004 M⊙. We detected, however, the disks associated with the younger stellar objects LkHα 198-IR and LkHα 198-mm that are located in the vicinity of LkHα 198. The fitting of the mm part of the SED reveal that the grains in the mid-plane of the disks around BD+61154, RR Tau, and VY Mon have sizes of ～1-C1000 μm. Therefore, grains have not grown to centimetre sizes in these disks yet. Conclusions. These massive (M· ≥ 3 M⊙) and young (～ 1 Myr) HAe stars are surrounded by massive (?0.04 M⊙) disks with grains of micron-millimetre sizes. Although grain growth is proceeding in these disks, their evolutionary stage is prior to the formation of planetesimals. These disks are less evolved than those detected around T Tauri and Herbig Be stars.