Variable accretion processes in the young binary-star system UY Aur

Abstract

We present new K-band spectroscopy of the UY Aur binary star system. Our data are the first to show H{sub 2} emission in the spectrum of UY Aur A and the first to spectrally resolve the Brγ line in the spectrum of UY Aur B. We see an increase in the strength of the Brγ line in UY Aur A and a decrease in Brγ and H{sub 2} line luminosity for UY Aur B compared to previous studies. Converting Brγ line luminosity to accretion rate, we infer that the accretion rate onto UY Aur A has increased by 2 × 10{sup –9} M {sub ☉} yr{sup –1} per year since a rate of zero was observed in 1994. The Brγ 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 mag 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 Brγ 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 Brγ 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.