Astronomy and Astrophysics – Astronomy
Scientific paper
May 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010dda....41.1003h&link_type=abstract
American Astronomical Society, DDA meeting #41, #10.03; Bulletin of the American Astronomical Society, Vol. 41, p.938
Astronomy and Astrophysics
Astronomy
Scientific paper
Debris disks are circumstellar dust disks seen orbiting young stars. Because these dust grains have short collisional lifetimes, there must also be a source for this dust, with collisions among unseen planetesimals being the likely culprit. One key question is the rate at which the planetesimal disk produces and ultimately sheds dust, and whether this mass loss due to planetesimal grinding is of cosmogonic significance. To address this, a model of a circumstellar debris disk is developed. Note that small circumstellar dust grains are susceptible to radiation pressure, which launches the smaller dust into wide orbits about the star (eg Strubbe and Chiang 2006). The resulting orbits are simple functions of grain size, so the calculation of dust-dust collision rates is straightforward. When the planetesimal disk's dust production rate is also accounted for, the result is a system of equations that governs over time the dust abundance versus grain size. Those equations are solved numerically, which yields a model debris disk whose principal parameters are the planetesimal disk's dust production rate and planetesimal disk radius. The model is then applied to Hubble Space Telescope observations of the debris disk orbiting beta Pictoris. Fitting the model to the observations allows one to infer that (1) the unseen planetesimal disk at beta Pic is broad and extends out to about r=130 AU, (2) the beta Pic dust grains are very asymmetric light-scatters (like interplanetary dust), and (3) beta Pic's inferred dust production rate is heavy, keeping in mind that the inferred dust production rate also depends sensitively on the dust grains' albedo. But even if the beta Pic grains are quite reflective, which lowers the inferred dust-production rate, the inferred mass-loss is still so heavy as to suggest that beta Pic might instead be a planetesimal-destroying system, rather than a planet-forming system.
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