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ISM Dust Grains and N-band Spectral Variability in the Spatially Resolved Subarcsecond Binary UY Aur

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 Added by Andrew Skemer
 Publication date 2010
  fields Physics
and research's language is English
 Authors Andrew Skemer




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The 10 micron silicate feature is an essential diagnostic of dust-grain growth and planet formation in young circumstellar disks. The Spitzer Space Telescope has revolutionized the study of this feature, but due to its small (85cm) aperture, it cannot spatially resolve small/medium separation binaries (<3; <420 AU) at the distances of the nearest star-forming regions (~140 pc). Large, 6-10m ground-based telescopes with mid-infrared instruments can resolve these systems. In this paper, we spatially resolve the 0.88 binary, UY Aur, with MMTAO/BLINC-MIRAC4 mid-infrared spectroscopy. We then compare our spectra to Spitzer/IRS (unresolved) spectroscopy, and resolved images from IRTF/MIRAC2, Keck/OSCIR and Gemini/Michelle, which were taken over the past decade. We find that UY Aur A has extremely pristine, ISM-like grains and that UY Aur B has an unusually shaped silicate feature, which is probably the result of blended emission and absorption from foreground extinction in its disk. We also find evidence for variability in both UY Aur A and UY Aur B by comparing synthetic photometry from our spectra with resolved imaging from previous epochs. The photometric variability of UY Aur A could be an indication that the silicate emission itself is variable, as was recently found in EX Lupi. Otherwise, the thermal continuum is variable, and either the ISM-like dust has never evolved, or it is being replenished, perhaps by UY Aurs circumbinary disk.



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We present new K-band spectroscopy of the UY Aur binary star system. Our data are the first to show H$_{2}$ emission in the spectrum of UY Aur A and the first to spectrally resolve the Br{gamma} line in the spectrum of UY Aur B. We see an increase in the strength of the Br{gamma} line in UY Aur A and a decrease in Br{gamma} and H$_{2}$ line luminosity for UY Aur B compared to previous studies. Converting Br{gamma} line luminosity to accretion rate, we infer that the accretion rate onto UY Aur A has increased by $2 times 10^{-9}$ M$_{odot}$ yr$^{-1}$ per year since a rate of zero was observed in 1994. The Br{gamma} line strength for UY Aur B has decreased by a factor of 0.54 since 1994, but the K-band flux has increased by 0.9 mags since 1998. The veiling of UY Aur B has also increased significantly. These data evince a much more luminous disk around UY Aur B. If the lower Br{gamma} luminosity observed in the spectrum of UY Aur B indicates an intrinsically smaller accretion rate onto the star, then UY Aur A now accretes at a higher rate than UY Aur B. However, extinction at small radii or mass pile-up in the circumstellar disk could explain decreased Br{gamma} emission around UY Aur B even when the disk luminosity implies an increased accretion rate. In addition to our scientific results for the UY Aur system, we discuss a dedicated pipeline we have developed for the reduction of echelle-mode data from the ARIES spectrograph.
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