Identification of Main Sequence Stars with Mid-Infrared Excesses Using GLIMPSE: Beta-Pictoris Analogs?

Astrophysics, abstract
astro-ph/0504447

From: Brian Uzpen [view email]

Date: Wed, 20 Apr 2005 17:08:42 GMT   (358kb)

Spitzer IRAC 3.6-8 micron photometry obtained as part of the GLIMPSE survey
has revealed mid-infrared excesses for 33 field stars with known spectral types
in a 1.2 sq. degree field centered on the southern Galactic HII region RCW49.
These stars comprise a subset of 184 stars with known spectral classification,
most of which were pre-selected to have unusually red IR colors. We propose
that the mid-IR excesses are caused by circumstellar dust disks that are either
very late remnants of stellar formation or debris disks generated by planet
formation. Of these 33 stars, 29 appear to be main-sequence stars based on
optical spectral classifications. Five of the 29 main-sequence stars are O or B
stars with excesses that can be plausibly explained by thermal bremsstrahlung
emission, and four are post main-sequence stars. The lone O star is an O4V((f))
at a spectrophotometric distance of 3233+ 540- 535 pc and may be the earliest
member of the Westerlund 2 cluster. Of the remaining 24 main-sequence stars, 18
have SEDs that are consistent with hot dusty debris disks, a possible signature
of planet formation. Modeling the excesses as blackbodies demonstrates that the
blackbody components have fractional bolometric disk-to-star luminosity ratios,
LIR/L*, ranging from 10^-3 to 10^-2 with temperatures ranging from 220 to 820
K. The inferred temperatures are more consistent with asteroid belts rather
than the cooler temperatures expected for Kuiper belts. Mid-IR excesses are
found in all spectral types from late B to early K.

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