Disks Around Intermediate Mass Stars in IC 1805
First Author:
Sidney Wolff
Email: swolff AT noao.edu
NOAO
P.O. Box 26732
Tucson, AZ 95726 USA
Coauthors:
L.M. Rebull, IPAC
S.E. Strom, NOAO
Abstract
We present the results of a study aimed at establishing the frequency and characteristics of circumstellar accretion disks surrounding intermediate mass (~2-6 solar masses) stars in the rich, young cluster (t ~1-2 Myr) IC 1805. Our dataset comprises optical (UBV), near-IR (2MASS), IRAC, and MIPS photometry and optical spectroscopy, which together enable identifying 218 cluster members, placing them in an HR diagram, determining their spectral energy distributions, and characterizing disk properties from the magnitude and shape of the excess infrared emission above photospheric levels. Our analysis suggests (a) that analogs of Herbig Ae/Be stars (stars surrounded by accretion disks whose dust component extends inward to the dust destruction radius) are rare (~3% of our sample); and (b) there are a significant (~$10% of the sample) number of stars (of spectral types ranging from B through early F) that exhibit infrared excesses, especially in the two longer IRAC bands, that seem best explained by assuming that they arise either from gaseous inner disks analogous to those that surround rapidly rotating Be stars, and similar to the Class III Herbig Ae/Be stars discussed by Hillenbrand et al. (1992) or from disks with inner holes. We discuss alternative explanations for these latter objects and conclude that they may be analogs of the so-called transition objects found among solar-type PMS stars (objects surrounded by accretion disks that are nearly dust-free in their inner regions, but dust rich outward of the dust-free zone).
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