Debris disks

Class I obj ects also have bipolar outflows, but they are less powerful and less well collimated than those of Class 0 objects. This stage lasts 100 000 to 200 000 years. Class //objects, also known as classical T Tauri stars, are pre-main-sequence stars with optically thick proto-planetary disks. They are no longer embedded in their parent cloud, and they are observed in optical and infrared wavelengths. They still exhibit bipolar outflows and strong stellar winds. This stage lasts from 1-10 million years. Class ///objects are the so-called weak line or naked T-Tauri stars. They have optically thin disks, perhaps debris disks in some cases, and there are no outflows or other evidence of accretion. They are observed in the visible and near infrared and have strong X-ray emission. These stars may have planets around them, although they cannot be observed. 

Debris disks (Meyer etal. 2007, Wyatt etal. 2008) Beta Pic Group (11 Myr, dyn de la Reza etal. 2006)... 

The collapse of rotating molecular cloud cores leads to the formation of massive accretion disks that evolve to more tenuous protoplanetary disks. Disk evolution is driven by a combination of viscous evolution, grain coagulation, photoevaporation, and accretion to the star. The pace of disk evolution can vary substantially, but massive accretion disks are thought to be typical for stars with ages < 1 Myr and lower-mass protoplanetary disks with reduced or no accretion rates are usually 1-8 Myr old. Disks older than 10 Myr are almost exclusively non-accreting debris disks (see Figs. 1.3 and 1.5). 

Figure 1.5 Left panel the young, accreting star-disk system HH30 seen edge-on at visible wavelengths. The optically thick disk occults the star and the scattered light image shows the flaring disk surface. The system also drives a powerful jet (NASA/Space Telescope Science Institute, Burrows et al. 1996). Right panel debris disk around the 12 Myr-old low-mass star AU Mic. The disk is geometrically flat, optically thin and depleted in gas (NASA/ESA/STScI).

Transition from protoplanetary disks to debris disks... 

Figure 9.1 Examples of spectral energy distributions from young Sun-like stars with circumstellar dust disks. Optically thick dust disks (solid line) have excess emission relative to the stellar photosphere over a broad wavelength range, from near-infrared to millimeter wavelengths. Transition disks (dashed line) lack near-infrared excess emission, but have large mid- and far-infrared emission. Debris disks (dotted line) have small excess emission starting at wavelengths typically longer than 10 pm. Primordial and transition disks often show a prominent 10 pm silicate emission feature from warm dust grains in the disk atmosphere.

There is no observational evidence yet for the presence of CAIs in protoplanetary or more evolved debris disks. In the following we attempt to constrain their time of formation by comparing their formation environment to that of disks in different evolutionary stages. With this approach we are implicitly assuming that CAIs are a common outcome of the disk-evolution and planet-formation process, which may not be the case. 

The daughter nuclide may be stable or unstable (radioactive), debris disk a circumstellar disk in which the majority of the dust is not derived from the collapsing molecular cloud, but from the collisions of minor bodies in the disk. The typical masses and optical depths of these disks are several orders of magnitudes lower than those typical to accretion disks, desorption changing from an adsorbed state on a surface to a gaseous or liquid state. 

Manoj and Bhatt, 2005 [215] investigated Vega like stars and their relation with dust disks. As parameter for the size and mass of the dust disks the fraction f dust/.f star was estimated. They found that debris disks seem to survive longer... 

Currie, T, Plavchan, R, Kenyon, S.J. A Spitzer study of debris disks in the young nearby cluster NGC 2232 icy planets are common around 1.5-3 MsoIm stars. Astrophys. J. 688,... 

Jura, M. Are there debris disks and Kuiper belt systems around first ascent red giants In Bulletin of the American Astronomical Society, vol. 37, p. 469 (2005)... 

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