Variable Accretion Processes in the Young Binary-Star System UY Aur

TL;DR

This study presents new spectroscopic observations of the UY Aur binary system, revealing variable accretion rates and emission lines, and introduces a specialized data reduction pipeline for ARIES spectrograph data.

Contribution

First spectroscopic resolution of Brγ in UY Aur B and detection of H₂ emission in UY Aur A, along with analysis of accretion variability and a new data reduction pipeline.

Findings

Accretion rate onto UY Aur A increased since 1994.

Brγ line strength in UY Aur B decreased, but its disk luminosity increased.

UY Aur A now accretes more than UY Aur B.

Abstract

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.