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Title: Palomar/triplespec observations of Spitzer/MIPSGAL 24 μm circumstellar shells: Unveiling the natures of their central sources

We present near-IR spectroscopic observations of the central sources in 17 circumstellar shells from a sample of more than 400 'bubbles' discovered in the Spitzer/MIPSGAL 24 μm survey of the Galactic plane and in the Cygnus-X region. To identify the natures of these shells, we have obtained J, H, and K band spectra with a resolution of ∼2600 of the stars at their centers. We observed 14 MIPSGAL bubbles (MBs), WR149, and 2 objects in the Cygnus-X region (WR138a and BD+43 3710), our sample being about 2.5 mag fainter in the K band than previous studies of the central sources of MBs. We use spectroscopic diagnostics and spectral libraries of late- and early-type stars to constrain the natures of our targets. We find five late-type giants. The equivalent widths of their CO 2.29 μm features allow us to determine the spectral types of the stars and hence derive the extinction along the line of sight, distance, and physical size of the shells. We also find 12 early-type stars: in 9 MBs and the 3 comparison objects. We find that the subtype inferred from the near-IR for WR138a (WN9h) and WR149 (WN5h) agrees with that derived from optical observations. A carefulmore » analysis of the literature and the environment of BD+43 3710 allows us to rule out the carbon star interpretation previously suggested. Our near-IR spectrum suggests that it is a B5 supergiant. At the centers of the nine MBs, we find a WC5-6 star possibly of low mass, a candidate O5-6 V star, a B0 supergiant, a B/A-type giant, and five luminous blue variable (LBV) candidates. We also report the detections of emission lines arising from at least two shells with typical extents (∼10''), in agreement with those in the mid-IR. We summarize the findings on the natures of the MBs since their discovery, with 30% of them now known. Most MBs with central sources detected in the near- to mid-IR have been identified and are red and blue giants, supergiants, or stars evolving toward these phases, including, in particular, a handful of newly discovered Wolf-Rayet stars and a significant number of LBV candidates.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4]
  1. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States)
  2. Infrared Processing and Analysis Center, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States)
  3. California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States)
  4. Gemini North Observatory, 670 North A'ohoku Place, Hilo, HI 96720 (United States)
Publication Date:
OSTI Identifier:
22342282
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (New York, N.Y. Online); Journal Volume: 148; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CARBON MONOXIDE; CARBON STARS; COMPARATIVE EVALUATIONS; DETECTION; DISTANCE; EMISSION; INFRARED SPECTRA; INTERMEDIATE INFRARED RADIATION; LIBRARIES; MASS; NEAR INFRARED RADIATION; RESOLUTION; SPECTROSCOPY; WOLF-RAYET STARS