Zoekopdracht:
journal id: "astronomyxandxastrophysics"
| Auteurs | C.P. Dullemond, C. Dominik | | Titel | Flaring vs. self-shadowed disks: The SEDs of Herbig Ae/Be stars |
| Tijdschrift | Astronomy and Astrophysics |
| Jaargang | 417 |
| Jaar | 2004 |
| Pagina's | 159-168 |
| ISSN | 00046361 |
| Faculteit | Faculteit der Natuurwetenschappen, Wiskunde en Informatica |
| Instituut/afd. | FNWI: Astronomical Institute Anton Pannekoek (IAP) |
| Trefwoorden | accretion, accretion disks; stars: circumstellar matter; stars: formation; stars: pre-main-sequence; infrared: stars |
| Samenvatting | Isolated Herbig Ae stars can be divided into two groups (Meeus et al. \citeyear{meeuswatersbouw:2001}): 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. |
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