COMMISSION 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 3823 Konkoly Observatory Budapest 4 January 1993 HU ISSN 0374 - 0676 PERIODIC LIGHT VARIATIONS IN TEN WEAK EMISSION T TAURI STARS IN TAURUS-AURIGA COMPLEX We present results of BVR photometry of 22 weak emission T Tauri stars (WTTS) discovered in the Lick CaII survey (Herbig et al. 1986) and in the x-ray survey (Feigelson et al. 1987). These WTTS stars are distinguished by the presence of significant Li abundances, strong chromospheric emission, and none of the excesses common to the CTTS. The properties of WTTS have been described by Walter (1987), Walter et al. (1988), Strom et al. (1989), and Skinner et al. (1991). The observations were obtained with the 48-cm reflector during 40 nights (August-September 1992) on Mt. Maidanak. The mean error of one observation of a program star is typically +-0.01 mag. in V, B-V, and V-R. We found rotation periods of 1.5-6.2 days for ten stars. The limits of the light variations, mean colours, number of observations, the period, and full amplitudes in B and V mag. are listed in Table I. Phase diagrams for light curve in the V filter for ten stars are displayed in Figure 1. [FIGURE 1] Figure 1. Phase diagrams for light curve in the V filter for ten WTTS These ten stars, together with the six stars (V819, V827, V830, V836 Tau, HDE 283572, and NTTS 041636+2743) monitored by Rydgren and Vrba (1983), Rydgren et al. (1984), Walter et al. (1987), Bouvier et al. (1988), and Grankin (1992), form a sample of sixteen WTTS stars with known rotation periods. Figure 2 shows the dependence of x-ray flux on axial rotation period for this sample WTTS stars and CTTS. The x-ray fluxes and the rotation periods are from Bouvier (1990) for CTTS and the x-ray fluxes from Walter et al. (1988) for WTTS. Despite a large scatter in the data, there is a trend toward decreasing F_x as the rotational period lengthens. The similar dependence of x-ray flux upon rotational period both in CTTS and in WTTS in Figure 2 points to a common magnetic origin for their x-ray emission. We do not find any obvious rotational modulation effect in the V magnitude variations of all others stars. In many cases, this may be explained by poor sample of observational sets of the stars. It is necessary to carry out UBVR monitoring of these objects in the future. Table I. WTTS stars in Tau-Aur. Star name n V_max V_min delta_V n P Delta TAP NTTS ** # days V B 4 032641+2420 26 12.06 12.22 12.15 0.046 0.87 8 0.82 9 034903+2431 22 12.14 12.27 12.19 0.033 1.06 5 1.01 10NE 035120+3154NE 26 11.91 12.35 12.20 0.111 0.88 - - 11 035135+2528A+B 23 12.31 12.43 12.39 0.026 0.92 5 0.86 SAO 76411 A 32 8.86 8.94 8.89 0.018 0.58 32 0.50 SAO 76411 B 31 10.39 10.45 10.42 0.028 0.88 31 0.73 14NE 040012+2545N+S 22 12.86 12.98 12.91 0.160 1.00 5 0.93 17 SAO 76428 31 9.46 9.53 9.48 0.017 0.53 31 0.47 26 041559+1716 25 12.16 12.36 12.27 0.135 1.12 9 0.98 2.52 .14 .18 35 042417+1744 30 10.24 10.37 10.31 0.031 0.78 30 0.66 2.74 .07 .08 39 *1 29 10.27 10.34 10.31 0.018 0.78 29 0.70 3.67 .04 .06 40 042835+1700 22 12.52 12.64 12.58 0.032 1.16 8 1.00 1.55 .10 .07 41 042916+1751 22 12.01 12.36 12.17 0.107 1.23 8 1.07 2.43 .25 .28 45 042950+1757 21 13.74 13.30 13.23 0.059 1.46 8 1.29 6.2 .10 .08 49 043124+1824 20 12.69 12.82 12.77 0.063 1.05 7 0.90 3.32 .07 .07 51S 043220+1815 29 10.92 11.02 10.96 0.024 0.83 29 0.73 3.2 .03 .03 56 045226+3013 28 10.75 10.92 10.84 0.040 1.02 28 0.86 2.24 .09 .09 57NW 045251+3016 25 11.53 11.67 11.60 0.050 1.29 20 1.11 LkCaII- 3 *2 26 12.02 12.77 12.07 0.046 1.50 11 7.53 LkCaII- 4 *2 25 12.31 12.83 12.57 0.144 1.42 11 1.34 3.37 .35 .38 LkCaII- 15 *2 22 11.98 12.59 12.16 0.173 1.26 7 1.13 LkCaII- 16 *2 17 12.50 12.71 12.60 0.052 1.54 2 1.40 Notes: ** delta_V is the standard deviation from the mean of the V magnitudes. # Number of observations for V-R colour. *1 None exhibit detectable Li I 6707 Angstrom. SB1. No orbit determined yet, v sin i=~30 km/s (Walter et al. 1988). *2 From Herbig et al. (1986), not observed in x-rays. [FIGURE 2] Figure 2. Dependence of x-ray flux on rotation period for TTS. WTTS are shown as empty circles and CTTS as filled circles. K.N. GRANKIN Astronomical Institute Academy of Sciences of Uzbekistan, Astronomical str. 33, 700052 Tashkent, Uzbekistan, CIS References: Bouvier, J.: 1990, Astron. J., 99, 946. [BIBCODE 1990AJ.....99..946B ] Bouvier, J. et al.: 1988, Astron. and Astrophys. Supp. Series, 75, 1. [BIBCODE 1988A&AS...75....1B ] Feigelson, E.D. et al.: 1987, Astron. J., 94, 1251. [BIBCODE 1987AJ.....94.1251F ] Grankin, K.N.: 1992, I.B.V.S., No. 3720. Herbig, G.H. et al.: 1986, Astron. J., 91, 575. [BIBCODE 1986AJ.....91..575H ] Rydgren, A.E. and Vrba, F.J.: 1983, Astrophys. J., 267, 191. [BIBCODE 1983ApJ...267..191R ] Rydgren, A.E. et al.: 1984, Astron. J., 89, 1015. [BIBCODE 1984AJ.....89.1015R ] Skinner, S.L. et al.: 1991, Astron. J., 102, 1742. [BIBCODE 1991AJ....102.1742S ] Strom, K.M. et al.: 1989, Astron. J., 97, 1451. [BIBCODE 1989AJ.....97.1451S ] Walter, F.M.: 1987, Publ. Astron. Soc. Pac., 99, 31. [BIBCODE 1987PASP...99...31W ] Walter, F.M. et al.: 1987, Astrophys. J., 314, 297. [BIBCODE 1987ApJ...314..297W ] Walter, F.M. et al.: 1988, Astron. J., 96, 297. [BIBCODE 1988AJ.....96..297W ]