Evolutionary timescales for circumstellar disks associated with solar-type pre-main sequence stars

Details Evolutionary timescales for circumstellar disks associated with solar-type pre-main sequence stars Evolutionary timescales for circumstellar disks associated with solar-type pre-main sequence stars

Jul 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990aipc..207...71s&link_type=abstract

Astrophysics from the Moon. AIP Conference Proceedings, Volume 207, pp. 71-86 (1990).

Astronomy and Astrophysics

Astrophysics

1

Circumstellar Shells, Clouds, And Expanding Envelopes, Circumstellar Masers, Infrared

Scientific paper

Excess infrared radiation above photospheric levels provides the basis for diagnosing the presence of circumstellar disks surrounding solar-type pre-main sequence (PMS) stars, and for determining the evolutionary timescales for these disks. Analysis of a large and representative sample of currently known solar-type PMS stars in Taurus-Auriga shows that for those stars with ages t<3 Myr, ~1/2 exhibit excess 2.2 μm and 10 μm emission consistent with that expected from optically thick disks extending inward to the stellar surface. By an age t~10 Myr, fewer than 10% of our sample show evidence of dust emission from optically thick disks, and hence must have accreted or destroyed their disks, or may have begun to assemble distributed gas and dust into larger bodies. Hence, the timescale over which disks survive as infrared-luminous, optically thick structures is t<=10 Myr. Out of a sample which contains 33 solar-type PMS stars surrounded by optically thick disks (typical age, t~3 Myr), 3 show evidence of inner holes. These holes are signified by small near-infrared (λ<=25 μm) excesses arising in optically thin regions located at r<1 AU, and large far-infrared excesses produced in regions r>~1 AU. Disks with inner holes may be ``transition structures'' which have begun to assemble material into larger bodies in the terrestrial planet region. The frequency of occurrence of transition structures in our sample suggests that a given disk evolves from an optically thick disk to an optically thin structure on a timescale, t~0.3 Myr. Those stars whose disks have become optically thin in their inner regions show no evidence of either 1) excess optical and ultraviolet radiation believed to be produced in a boundary layer, or 2) strong Hα and broad forbidden line emission thought to arise in energetic winds.

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