Photometric Variability Properties of 21 T Tauri and Related Stars from AAVSO Visual Observations

Abstract T Tauri variables are sun-like stars in various stages of their birth. Wehave analyzed long-term AAVSO visual observations of 21 T Tauri and relatedstars, using Fourier and self-correlation techniques. This follows our previousstudy of eleven such stars in JAAVSO 35 , 290 (2006). Only a few of the variablesshowed periodic behavior, but self-correlation analysis makes it possible toconstruct a “variability profile”—amount of variability versus time scale—for allthe stars, not just the periodic ones. For some of the periodic variables, we havestudied the long-term behavior of the periods and amplitudes: T Cha and HT Lupappear to be rotating variables with stable periods less than 10 days; RU Lup,UX Ori, and TU Phe appear to show transient cycles of typically 50–500 days,probably arising in the accretion disc. R CrA has a stable 66-day period, whichwould be unusually long for a rotation period; its cause is not clear. We alsodiscuss interesting but spurious low-amplitude one-year and one-monthperiodicities which occur in a few of the stars. Finally: we comment on the star AQDra, an RR Lyrae star, originally classified as a T Tauri star with a 5.5-day period.1. IntroductionT Tauri stars are sun-like stars in various stages of birth, with or without anaccretion disc still present. Although they are all photometrically variable, theyare defined spectroscopically , on the basis of various emission lines and lithiumlines being present in the spectrum. The types and causes of photometricvariability include: (i) strict periodicity (periods 0.5 to several days) due to rotationof a spotted star; (ii) rapid flickering connected with accretion onto the star; (iii)slow variations due to variations in the rate of accretion; (iv) quasi-periodic