NOAO >   Observing Info >   Approved Programs >   2009B-0523

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Proposal Information for 2009B-0523


PI: You-Hua Chu, University of Illinois, yhchu@illinois.edu
Address: Astronomy Department, 1002 West Green Street, Urbana, IL 61801, USA

CoI: Maxwell Schoenoff, University of Illinois
CoI: Sean Points, NOAO/CTIO
CoI: Rosie Chen, University of Virginia
CoI: Robert A. Gruendl, University of Illinois

Title: Nature of Blue Stars with IR Excesses: Young or Evolved

Abstract: Stars with circumstellar dust exhibit IR excesses. Both young stellar objects (YSOs) still enshrouded in dust and evolved stars with dusty mass loss exhibit IR excesses. It is thus often difficult to differentiate between YSOs and evolved stars, such as post-AGB stars and luminous blue variables (LBVs), based on broad-band spectral energy distributions alone. Using the Spitzer survey of the Large Magellanic Cloud (LMC), we have identified ~3000 YSO candidates, among which ~100 have blue optical counterparts with U-B < 0. Only about 1/2 of these blue stars with IR excesses have colors and magnitudes consistent with O or B type stars. Using pilot long-slit spectra obtained with the Goodman spectrograph, we were able to differentiate among young stars in HII regions, YSOs without compact HII regions, and LBVs in ejecta nebulae. We request spectroscopic observations for blue stars with IR excesses in the LMC in order to determine whether they are YSOs or evolved stars. The spectral classifications of YSOs in conjunction with IR spectral energy distributions can be used to test radiative transfer models. The identification of evolved blue stars will help us find quiescent LBVs and blue supergiants similar to SN 1987A's progenitor, and further inventory dust production by massive stars.


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