PF-02-0057

Twenty-five years of variable accretion onto TW Hya

Gregory J Herczeg

TW Hya serves as a benchmark for many accretion disk studies. In this poster, we estimate accretion using veiling measurements in 1178 spectra of TW Hya obtained over the past 25 years. TW Hya is not a weak accretor, with an average accretion rate of 2.5e-9 Msun/yr (standard deviation of 0.2 dex) that is only slightly lower than the accretion rate expected for its mass, based on complete samples of younger disks in the Lupus and Chamaeleon star-forming regions. He line luminosities are well correlated with accretion, but variability in other lines should not be used to infer variable accretion luminosity. The structure function indicates that accretion rates reset every ~1.6 days, although the lightcurve includes short bursts and epochs of stronger and weaker accretion.