ar X iv : a st ro - p h / 06 05 41 5 v 1 1 7 M ay 2 00 6 revised version Dust Processing in Disks around T Tauri Stars
نویسندگان
چکیده
The 8–14 µm emission spectra of 12 T Tauri stars in the Taurus/Auriga dark clouds and in the TW Hydrae association obtained with the Infrared Spectro-graph (IRS 1) on board Spitzer are analyzed. Assuming the 10 µm features originate from silicate grains in the optically thin surface layers of T Tauri disks, the 8–14 µm dust emissivity for each object is derived from its Spitzer spectrum. The emissivities are fit with the opacities of laboratory analogs of cosmic dust. The fits include small nonspherical grains of amorphous silicates (pyroxene and olivine), crystalline silicates (forsterite and pyroxene), and quartz, together with large fluffy amorphous silicate grains. A wide range in the fraction of crystalline silicate grains as well as large silicate grains among these stars are found. The dust in the transitional-disk objects CoKu Tau/4, GM Aur, and DM Tau has the simplest form of silicates, with almost no hint of crystalline components and modest amounts of large grains. This indicates that the dust grains in these objects have been modified little from their origin in the interstellar medium. Other – 2 – stars show various amounts of crystalline silicates, similar to the wide dispersion of the degree of crystallinity reported for Herbig Ae/Be stars of mass < 2.5 M ⊙. Late spectral type, low-mass stars can have significant fractions of crystalline silicate grains. Higher quartz mass fractions often accompany low amorphous olivine-to-amorphous pyroxene ratios. It is also found that lower contrast of the 10 µm feature accompanies greater crystallinity.
منابع مشابه
ar X iv : a st ro - p h / 03 05 19 5 v 1 1 2 M ay 2 00 3 The First Detailed Look at a Brown Dwarf Disk
The combination of mid-infrared and recent submm/mm measurements allows us to set up the first comprehensive spectral energy distribution (SED) of the circumstellar material around a young Brown Dwarf. Simple arguments suggest that the dust is distributed in the form of a disk. We compare basic models to explore the disk parameters. The modeling shows that a flat disk geometry fits well the obs...
متن کاملar X iv : a st ro - p h / 06 05 46 4 v 1 1 8 M ay 2 00 6 Mid - Infrared Spectroscopy of Disks around Classical T Tauri Stars
We present the first Spitzer Infrared Spectrograph 11 observations of the disks around classical T Tauri stars: spectra in the 5.2-30 µm range of six stars. The spectra are dominated by emission features from amorphous silicate dust, and a continuous component from 5 to 8 µm that in most cases comprises an excess above the photosphere throughout our spectral range. There is considerable variati...
متن کاملar X iv : a st ro - p h / 06 05 29 4 v 1 1 1 M ay 2 00 6 Why Do T Tauri Disks Accrete ?
Observations of T Tauri stars and young brown dwarfs suggest that the accretion rates of their disks scale strongly with the central stellar mass, approximately Ṁ ∝ M ∗ . No dependence of accretion rate on stellar mass is predicted by the simplest version of the layered disk model of Gammie (1996), in which non-thermal ionization of upper disk layers allows accretion to occur via the magnetorot...
متن کاملar X iv : a st ro - p h / 05 03 46 6 v 1 2 2 M ar 2 00 5 The Differential Lifetimes of Protostellar Gas and Dust Disks 1
We construct a protostellar disk model that takes into account the combined effect of viscous evolution, photoevaporation and the differential radial motion of dust grains and gas. For T Tauri disks, the lifetimes of dust disks that are mainly composed of millimeter sized grains are always shorter than the gas disks’ lifetimes, and become similar only when the grains are fluffy (density . 0.1 g...
متن کامل