Dust disks

P/Hartley 2 observed with the Infrared Space Observatory. In Thermal Emission Spectroscopy and Analysis of Dust, Disks, and Regoliths, ASP Conference 196, eds. Sitko, M. L., Sprague, A. L. and Lynch, D. K., San Francisco Astronomical Society of the Pacific, pp. 109-117. 

IC 348 and Chamaeleon I star-forming regions 2 Myr, warm dust disks around -50-65% of stars (Luhman 2008)... 

Observations of near-infrared excess emission from hundreds of disks with ages covering the first 10 Myr demonstrate fundamental structural evolution and the eventual loss of the fine dust from the inner disk (< 1AU). The declining fraction of stars with dust disks suggests a disk half-life of 3 to 5 Myr (see Chapter 9, e.g. Hernandez et al. 2007). Longer-wavelength infrared observations, primarily from the Spitzer Space Telescope, show a similar picture for the intermediate disk radii (1-5 AU). The combination of these lines of evidence is interpreted as a rapid (< 1-3 Myr) dispersal of the fine dust in most systems, probably progressing inside-out. 

Although the disk mass is dominated by hydrogen, much less is known about its dispersal. Tracers of hot gas in the innermost disk regions show a one-to-one correspondence to the presence of hot dust (Harfigan et al. 1995) and gas accretion to the stars declines at the same rate as hot dust disperses. Spitzer studies of mid-infrared ro-vibrational lines probe warm gas on orbits similar to Jupiter s and demonstrate the loss of gas in few tens of millions of years (Pascucci et al. 2007). Gas in the coldest disk regions can be traced through CO rotational lines such studies also suggest a gas depletion by 10 Myr. The combined astronomical evidence shows that (1) dust disks dissipate in 3—8 Myr via rapid inside-out dispersal (2) gas dissipates in a similar, or perhaps even shorter timescale. 

Turbulent mixing and dust disk evolution models for a range of stellar and disk masses correlations are much easier to observe and more difficult to fit than simulations restricted to the minimum-mass solar nebula... 

The above discussion provides the basis for using the infrared excess relative to the photospheric flux as a tool to detect primordial dust disks and determine the timescale over which they disperse. We should note that emission at infrared... 

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.

Backman D. E., Fajardo-Acosta S. B., Stencel R. E., and Stauffer J. R. (1997) Dust disks around main sequence stars. Astrophys. Space Sci. 255, 91-101. 

Gases and grains in interstellar clouds probably experienced many shock events during the formation of planetesimals and meteorites. These events are as follows 1) coagulation of dust into clumps, which settle to the equatorial plane of the nebula 2) breakup of the gravitationally unstable dust disk into clusters of dust clumps 3) coalescence of the clusters into 1 km planetesimals ... 

Kalas, P. and Jewitt, R, 1995. Assymetries in the Beta Pictoris dust disk. Astron. J., 110, 794-804. 

K. Wood, Infrared signatures and models of circumstellar dust disks. New Astron. Rev. 52(2), 145-153(2008)... 

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... 

Manoj, R, Bhatt, H.C. Kinematics of Vega-like stars lifetimes and temporal evolution of circumstellar dust disks. Astron. Astrophys. 429, 525-530 (2005)... 

Key wordsi Dust disks - Instrumentation 10 /cm array imaging - Main-sequence stars individual (fi Pictoris, 51 Ophiuchi). 

---