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

TL;DR

This study spatially resolves the binary UY Aur in mid-infrared, revealing dust grain properties and variability in silicate features, providing insights into dust evolution and disk processes in young stellar objects.

Contribution

First spatially resolved mid-infrared spectra of UY Aur binary, comparing with past unresolved data to study dust grain properties and variability.

Findings

UY Aur A has pristine, ISM-like grains.

UY Aur B shows an unusual silicate feature due to blended emission and absorption.

Both components exhibit variability in their spectra and photometry.

Abstract

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 Aur's circumbinary disk.