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==> In this proposal, more time is being requested for SVWB.SBDSK4
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We propose to test the hypothesis that stellar angular momentum is regulated
during the pre-main sequence phase via coupling of the star to its
circumstellar disk.  Previous work has shown that classical T Tauri stars
with massive circumstellar disks (0.01 Msun) rotate more slowly than their
weak-emission counterparts which lack such disks.  These observations
found a natural explanation in models where the evolution of stellar angular
momentum is regulated through magnetic coupling with a circumstellar disk.  A
sample of 10 rapidly rotating (P < 1 day) and 10 slowly rotating (P > 1 day)
solar-mass stars has been selected in the young open cluster Alpha Per.  We will
survey these stars with the ISOPHOT instrument in order to detect the presence
of optically-thin remnant circumstellar disks. Recent models suggest that
solar-type stars with rotation periods much greater than 1 day should have
remained coupled to their disks for greater than 10 Myr. Remnant disks around
the slowest rotating (P ~ 6 days) stars in Alpha Per cluster (age 50 Myr) should
have just begun to dissipate after the termination of the disk-locking phase.
With these carefully designed ISO measurements we should be able to; i) examine
the connection between stellar rotation and the presence of disk material;
and ii) determine the overall frequency of optically-thin circumstellar
material around low-mass stars in Alpha Per. This proposal is a key component
of a two-part follow-up to the program EVOLUTION OF CIRCUMSTELLAR DISKS by
Beckwith et al. awarded GTO time in the first ISO call for proposals.