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Title: Herbig stars' near-infrared excess: An origin in the protostellar disk's magnetically supported atmosphere

Young stars with masses 2-8 times solar, the Herbig Ae and Be stars, often show a near-infrared excess too large to explain with a hydrostatically supported circumstellar disk of gas and dust. At the same time, the accretion flow carrying the circumstellar gas to the star is thought to be driven by magnetorotational turbulence, which, according to numerical MHD modeling, yields an extended low-density atmosphere supported by the magnetic fields. We demonstrate that the base of the atmosphere can be optically thick to the starlight and that the parts lying near 1 AU are tall enough to double the fraction of the stellar luminosity reprocessed into the near-infrared. We generate synthetic spectral energy distributions (SEDs) using Monte Carlo radiative transfer calculations with opacities for submicron silicate and carbonaceous grains. The synthetic SEDs closely follow the median Herbig SED constructed recently by Mulders and Dominik and, in particular, match the large near-infrared flux, provided the grains have a mass fraction close to interstellar near the disk's inner rim.
Authors:
 [1] ; ;  [2] ;  [3]
  1. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)
  2. Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany)
  3. Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showamachi, Kanazawa-ku, Yokohama, Kanagawa 236-0001 (Japan)
Publication Date:
OSTI Identifier:
22348336
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 780; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ATMOSPHERES; DENSITY; DUSTS; ENERGY SPECTRA; LUMINOSITY; MAGNETIC FIELDS; MAGNETOHYDRODYNAMICS; MASS; MONTE CARLO METHOD; OPACITY; PROTOPLANETS; RADIANT HEAT TRANSFER; RESONANCE IONIZATION MASS SPECTROSCOPY; SIMULATION; STARS; TURBULENCE