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J/A+A/299/89             COYOTES II                             (Bouvier+, 1995)
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COYOTES II: Spot properties and the origin of photometric period variations in
T Tauri stars
      Bouvier J., Covino E., Kovo O., Martin E.L., Matthews J.M.,
      Terranegra L., Beck S.C.
     <Astron. Astrophys. 299, 89 (1995)>
     =1995A&A...299...89B       (SIMBAD/NED BibCode)
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ADC_Keywords: Stars, pre-main sequence; Photometry, UBVRI
Keywords: stars: pre-main sequence - stars: rotation - stars: activity -
          accretion, accretion disks

Abstract:
    We present the results of a new multi-site campaign (COYOTES II) to
    monitor the light variations of T Tauri stars (TTS) of the
    Taurus-Auriga dark cloud. The UBVRI light curves of 19 TTS were
    obtained over a two months period to search for rotational modulation
    by spots. We report new period detections for IQ Tau (6.25d), LkCa-3
    (7.2d), and LkCa-14 (3.35d) and confirm previously detected periods
    for DF Tau (9.8d), DR Tau (9.0d), GM Aur (11.9d), and TAP 26 (2.58d).
    We also report tentative periods for CW Tau (8.2d), CY Tau (7.9d), HP
    Tau (5.9d), and XZ Tau (2.6d). No periods were found in the present
    data set for CI Tau, DG Tau, DQ Tau, GH Tau, RY Tau, Hubble 4, TAP 45,
    and TAP 57NW. Altogether, the results of this new campaign confirm the
    main conclusion of COYOTES I that classical T Tauri stars
    (CTTS) on average have longer rotational periods than weak-line TTS
    (WTTS). The present study also confirms that rotational modulation in
    WTTS is due to spots cooler than the photosphere and we show that the
    amplitude of the modulation primarily reflects the amount of areal
    coverage by spots. The amplitude of the light variations, and hence
    the spot size, is found to increase with both rotation rate and
    advancing spectral type, as expected if WTTS cool spots correspond to
    photospheric regions of strong dynamo-generated magnetic fields.
    Finally, combined with previous studies, these new results provide
    further evidence for temporal variations of the photometric periods of
    CTTS. Such variations seem to occur preferentially in CTTS whose
    rotational modulation is dominated by hot spots and we therefore argue
    that the observed period changes are linked to the magnetospheric
    accretion process rather than to surface differential rotation.


File Summary:
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  FileName      Lrecl  Records   Explanations
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ReadMe             80        .   This file
table1             54      374   UBVRI photometry
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Byte-by-byte Description of file: table1
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   Bytes Format  Units   Label    Explanations
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   1-  9  A9     ---     Name     Star name
  11- 17  A7     ---     HBC      HBC number (Herbig Bell Catalog)
  19- 28  F10.2  d       JD       Julian date
  30- 34  F5.2   mag     Vmag     V magnitude
  36- 39  F4.2   mag     B-V      []? B-V colour
  41- 44  F4.2   mag     U-B      []? U-B colour
  46- 49  F4.2   mag     V-R      []? V-R colour
  51- 54  F4.2   mag     V-I      []? V-I colour
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See also:
    V/73A   (HBC Catalogue, Lick Obs. Bull. 1111)
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(End)                                           Patricia Bauer [CDS] 16-Jan-1995