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Observational constraints on dust disk lifetimes : implications for planet formation

Hillenbrand, L.A. (2008) Observational constraints on dust disk lifetimes : implications for planet formation. In: A Decade of extrasolar planets around normal stars : proceedings of the Space Telescope Science Institute Symposium, held in Baltimore, Maryland May 2-5, 2005. Space Telescope Science Institute Symposium Series. No.19. Cambridge University Press , New York, pp. 84-105. ISBN 9780521897846.

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Thus far our impressions regarding the evolutionary time scales for young circumstellar disks have been based on small number statistics. Over the past decade, however, in addition to preci- sion study of individual star/disk systems, substantial observational effort has been invested in obtaining less detailed data on large numbers of objects in young star clusters. This has resulted in a plethora of information now enabling statistical studies of disk evolutionary diagnostics. Along an ordinate one can measure disk presence or strength through indicators such as ul- traviolet/blue excess or spectroscopic emission lines tracing accretion, infrared excess tracing dust, or millimeter flux measuring mass. Along an abscissa one can track stellar age. While bulk trends in disk indicators versus age are evident, observational errors affecting both axes, combined with systematic errors in our understanding of stellar ages, both cloud and bias any such trends. Thus detailed understanding of the physical processes involved in disk dissipation and of the relevant time scales remains elusive. Nevertheless, a clear effect in current data that is unlikely to be altered by data analysis improvements is the dispersion in disk lifetimes. Inner accretion disks are traced by near-infrared emission. Moderating a generally declining trend in near-infared continuum excess and excess frequency with age over <1 to 8±4 Myr, is the fact that a substantial fraction of rather young (<1 Myr old) stars apparently have already lost their inner accretion disks while a significant number of rather old (8-16 Myr) stars apparently still retain inner accretion disks. The age at which evidence for inner accretion disks ceases to be apparent for the vast majority (~90%) of stars is in the range 3-8 Myr. More distant, terrestrial zone dust is traced by mid-infrared emission where sufficient sensitivity and uniform data collec- tion are only now being realized with data return from the Spitzer Space Telescope. Constraints on mid-disk dissipation and disk clearing trends with radius are forthcoming.

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Additional Information:© Cambridge University Press 2008. Hardback: ISBN-13: 9780521897846 (June 2008); Adobe eBook Reader: ISBN-13: 9780511451072 (July 2008)
Subject Keywords:Extrasolar planets; Stars with planets; Normal stars
Series Name:Space Telescope Science Institute Symposium Series
Issue or Number:19
Record Number:CaltechAUTHORS:HILstsiss08
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:9577
Deposited By: Lindsay Cleary
Deposited On:06 Feb 2008
Last Modified:03 Oct 2019 00:01

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