COYOTES .1. MULTISITE UBVRI PHOTOMETRY OF 24 PRE-MAIN-SEQUENCE STARS OF THE TAURUS-AURIGA CLOUD

We present the results of a multi-site photometric campaign to monitor T Tauri stars in the Taurus-Auriga stellar formation region. The camp aign - dubbed COYOTES, for Coordinated Observations of Young Stellar O bjecTs from Earthbound Sites - yielded U BV RI magnitudes of 13 classi cal T Tauri stars, 10 weak-line T Tauri stars, and one suspected Ae He rbig star during 3 months between November 1990 and February 1991. Thi s database is well suited to search for periodic variations from about 1 day up to around 6 weeks, significantly extending the range of time scales properly sampled for T Tauri stars. We find evidence for period ic light variability in all 24 stars of our sample. More precisely, ph otometric periods axe detected in 18 stars at or above the 90% probabi lity level in several photometric bands simultaneously (BD+24-degrees- 676, DF Tau, DG Tau, DI Tau, DK Tau, DR Tau, GG Tau, GK Tau, IP Tau, R Y Tau, GM Aur, LkCa-15, IW Tau, LkCa-4, LkCa-7, LkCa-19, TAP 26, TAP 4 0), while probable periods, which require confirmation, are reported f or 4 other stars (DE Tau, LkCa-21, TAP 41, TAP 57NW), and upper limits on the photometric period axe derived for the 2 remaining stars (SU A ur, TAP 9). Light curve analysis and the origin of the variations are discussed in a companion paper (Bouvier et al. 1993, Paper 2).