Bibcode
Bouvier, J.; Cabrit, S.; Fernandez, M.; Martin, E. L.; Matthews, J. M.
Bibliographical reference
Astronomy and Astrophysics, Vol.272, NO. 1/MAYI, P. 176, 1993
Advertised on:
5
1993
Journal
Citations
400
Refereed citations
355
Description
In a multi-site photometric campaign to monitor T Tauri stars (TTS) in
the Taurus-Auriga cloud over more than two months - dubbed Coordinated
Observations of Young ObjecTs from Earthbound Sites (COYOTES), we find
all 24 of our target stars show evidence for periodic light variations
with periods between 1.2 and 24.0 days. This more than doubles the
number of periods published for Tan-Aur TTS. The variations of 20 of
these stars can be interpreted as rotational modulation of the stellar
flux by surface spots. The periods of the four remaining stars (RY Tan,
BD+24°676, TAP 26, and LkCa-21) may correspond to orbital periods of
binary systems. Models of the UBVRI light curves lead to the properties
of the spots, both hotter and cooler than the photo spheric temperature,
which appear to be the principal source of the photometric variability
of TTS on timescales of days and weeks.
The longest rotational period we measure (12 d, for GM Aur) leads to an
equatorial velocity of 8km s-1, which confirms the paucity of
extremely slow rotators (Veq ≤ ≤ 10km s-1)
among TTS younger than 5 106 yrs. Combining our 20 rotational
periods with those published for 17 other Tan-Aur TTS, we find that the
Weak-line TTS (EW(Hα) < 10Å) rotate faster than Classical
TTS (EW(Hα) ≥ 10Å) at the 99.9% confidence level
(according to a K-S test). The mean rotational period for the 11 WTTS is
4.1±1.7d; for the l5 CTTS, 7.6±2.1d. We interpret this
difference as evidence that WTTS spin-up as they contract on their
convective tracks, while CTTS are prevented from doing so by either (a)
their strong winds carrying away excess angular momentum and/or (b) a
magnetic coupling between the stars and their inner accretion disks, as
suggested by recent models. We discuss the implications of this
interpretation for the subsequent evolution of TTS toward the main
sequence. In particular, we propose that the different rotational
histories of WTTS and CTTS on their convective tracks may account for
the large range of rotational velocities observed among low-mass dwarfs
in young clusters.