An Amazingly Dusty Sun-like Star: Cosmic Collisions at 1 AU

Details An Amazingly Dusty Sun-like Star: Cosmic Collisions at 1 AU An Amazingly Dusty Sun-like Star: Cosmic Collisions at 1 AU

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004aas...20512707z&link_type=abstract

American Astronomical Society Meeting 205, #127.07; Bulletin of the American Astronomical Society, Vol. 36, p.1554

Biology

Scientific paper

We report extraordinary mid-infrared excess emission around a solar-type star of estimated age a few hundred million years. Ground-based mid-IR observations confirm that a strong IRAS 12 and 25 micron source is in fact located on the star and that the 12 micron emission appears point-like down to the diffraction limit of the Keck telescope ( ˜ 0."2). A simple blackbody fit to the excess indicates a ˜ 420 K dusty disk located ≲ 1 AU from the central star with a huge infrared fractional luminosity (tau) of ˜5%. This is to be compared to tau (= L[IR]/L[star]) of main sequence Vega-like stars which are < 0.1%. In addition, at Vega-like stars, dust temperatures are typically < 100 K.
A Keck LWS 8-13 micron low resolution spectrum shows strong silicate emission at ˜ 11.3 microns, confirmed by an R = 1,000 Gemini Michelle spectrum. The strength of the feature implies the typical grain size should not be much bigger than ˜ 1 micron. Constraints imposed by the broadband spectrum from 3.5 to 60 microns support the small grain sizes deduced from the silicate feature. In addition, the IRAS 60 micron upper limit places a strong upper limit on the quantity of cold dust grains.
At only 1 AU from the central star, small grains cannot survive long. The collisional grinding timescale is ˜ 100 yrs and grains fractured to smaller than a few tenths of a micron will be quickly blown away by radiation pressure. The Poynting-Roberton drag timescale for 1 micron dust is only a few thousand years. Therefore, all grains in the system should be second generation.
What can generate such a unique -- high temperature and high tau -- dusty disk? Perhaps the most plausible explanation is recent and frequent collisions between numerous planetesimals (asteroids?) near 1 AU.
This research was supported in part by NASA's Astrobiology Institute.

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