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Thomas Bensby. Profile photo.

Thomas Bensby

Senior lecturer

Thomas Bensby. Profile photo.

A glimpse into the nature of galactic mid-IR excesses


  • B. Uzpen
  • H. A. Kobulnicky
  • D. R. Semler
  • T. Bensby
  • C. Thom

Summary, in English

We investigate the nature of the mid-IR excess for 31 intermediate-mass stars that exhibit an 8 μm excess in either the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire or the Mid-Course Space Experiment using high-resolution optical spectra to identify stars surrounded by warm circumstellar dust. From these data we determine projected stellar rotational velocities and estimate stellar effective temperatures for the sample. We estimate stellar ages from these temperatures, parallactic distances, and evolutionary models. Using MIPS [24] measurements and stellar parameters we determine the nature of the infrared excess for 19 GLIMPSE stars. We find that 15 stars exhibit Ha emission and four exhibit Ha absorption. Assuming that the mid-IR excesses arise in circumstellar disks, we use the Ha fluxes to model and estimate the relative contributions of dust and free-free emission. Six stars exhibit Ha fluxes that imply free-free emission can plausibly explain the infrared excess at [24]. These stars are candidate classical Be stars. Nine stars exhibit Ha emission, but their Ha fluxes are insufficient to explain the infrared excesses at [24], suggesting the presence of a circumstellar dust component. After the removal of the free-free component in these sources, we determine probable disk dust temperatures of Tdisk ≃ 300-800 K and fractional infrared luminosities of LIR/L* ≃ 10 -3. These nine stars may be pre-main-sequence stars with transitional disks undergoing disk clearing. Three of the four sources showing Ha absorption exhibit circumstellar disk temperatures ≃300-400 K, LIR/ L* ≃ 10-3, IR colors K - [24] < 3.3, and are warm debris disk candidates. One of the four Ha absorption sources has K - [24] > 3.3 implying an optically thick outer disk and is a transition disk candidate.

Publishing year







Astrophysical Journal





Document type

Journal article


American Astronomical Society


  • Astronomy, Astrophysics and Cosmology


  • Circumstellar matter
  • Line: profiles
  • Stars: emission-line, Be
  • Stars: fundamental parameters
  • Stars: rotation
  • Techniques: spectroscopic




  • ISSN: 0004-637X