Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...447..391d&link_type=abstract
Astrophysical Journal v.447, p.391
Astronomy and Astrophysics
Astronomy
4
Infrared: Stars, Radiative Transfer, Stars: Circumstellar Matter, Stars: Emission-Line, Be, Stars: Individual Alphanumeric: Lkh Alpha 101, Stars: Pre-Main-Sequence
Scientific paper
Operating slightly beyond the formal diffraction limit of a 3 m telescope, we have obtained λ = 10 microns images with subarcsecond spatial resolution of the pre-main-sequence emission-line star LkHα 101. Our measurements show that mid-infrared radiation emanates from within 135 AU of the star, on the same spatial scale as a strong ionized wind deduced from radio observations. The point-spread function of our infrared instrument, at the 3 m Shane Telescope, has FWHM 0".740±0".022, as measured for the unresolved star α Tau. Raw images of the core component of LkHα 101 have FWHM 0".768±0".021 after deconvolution, we set a 95% confidence upper limit of 0".34 (270 AU) for the FWHM diameter of the core. Our measured flux density of 325±27 Jy for the unresolved core accounts for most of the 10 microns emission from the central arcminute of LkHα 101.
Our observation implies that ≍12% of the total luminosity of LkHα 101 is radiated by this unresolved core; thus, the unresolved core emission must be either optically thin, or anisotropically distributed about the star. For optically thin emission from dust, graphite or glassy carbon grains with radii less than α ≍ 0.15 microns can be excluded as contributing significantly to the unresolved 10 microns emission based on our upper limit of the source size and our measurement of the flux density, along with the observed spectrum. Similarly, silicate grains with radii less than α ≍ 0.3 microns can be excluded; although, based on the spectrum, silicate grains of any size are unlikely a dominant source of the mid-infrared core emission, if optically thin. The observation of an ionized stellar wind suggests as a model for the unresolved core a spherically symmetric, optically thin envelope of dust with an r-2 density distribution (characteristic of a uniform outflow). This model is consistent with our observations and with the spectral energy distribution, if the dust grains are graphite or glassy carbon and have radii a confined to the range 0.3 ≲ α ≲ 0.5 μm. An optically thin r-2 distribution composed primarily of other sizes of graphite and glassy carbon grains, or some other forms of carbon grains, would be inconsistent with the size we measure or the spectral energy distribution of the source. Alternatively, isothermal concentrations of dust of any size and composition that are optically thick even at λ = 10 μm, distributed anisotropically around the star, could produce the mid-infrared core emission. This dust cannot lie in a circumstellar disk because the near- to mid-infrared spectrum of LkHα 101 is inconsistent with that expected for a disk. If the unresolved 10 microns emission is produced by isothermal concentrations of dust optically thick at λ = 10 μm, then the concentrations must lie near a single radius from the star.
Bloemhof Eric E.
Danen R. M.
Gwinn Carl R.
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