Query : 2004A&A...417..159D

2004A&A...417..159D - Astronomy and Astrophysics, volume 417, 159-168 (2004/4-1)

Flaring vs. self-shadowed disks: The SEDs of Herbig Ae/Be stars.


Abstract (from CDS):

Isolated Herbig Ae stars can be divided into two groups (Meeus et al., 2001A&A...365..476M): those with an almost flat spectral energy distribution in the mid-infrared (``group I''), and those with a strong decline towards the far-infrared (``group II''). In this paper we show that the group I vs. II distinction can be understood as arising from flaring vs. self-shadowed disks. We show that these two types of disks are natural solutions of the 2D radiation-hydrostatic structure equations. Disks with high optical depth turn out to be flaring and have a strong far-IR emission, while disks with an optical depth below a certain threshold drop into the shadow of their own puffed-up inner rim and are weak in the far-IR. In spite of not having a directly irradiated surface layer, self-shadowed disks still display dust features in emission, in agreement with observations of group II sources. We propose an evolutionary scenario in which a disk starts out with a flaring shape (group I source), and then goes through the process of grain growth, causing the optical depth of the disk to drop and the disk to become self-shadowed (group II source). We show that this scenario predicts that the (sub-)millimeter slope of the disk changes from steep (small grains) to Rayleigh-Jeans-like (large grains) in the early stages of evolution, so that all group II sources are expected to have Rayleigh-Jeans-like slopes, while some group I sources may still have steep (sub-) millimeter slopes.

Abstract Copyright:

Journal keyword(s): accretion, accretion disks - stars: circumstellar matter - stars: formation - stars: pre-main-sequence - infrared: stars

Simbad objects: 2

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Number of rows : 2
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 HD 31648 Ae* 04 58 46.2655706952 +29 50 36.987625680 7.84 7.78 7.62 7.76 7.43 A5Vep 494 0
2 HD 36121 * 05 29 05.8870930440 -07 46 38.759252196   9.26 8.98     A9IV/V 20 0

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