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J/A+A/303/137       EROS Variables: Cepheids in the bar of LMC  (Beaulieu+ 1995)
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EROS variable stars: fundamental-mode and first-overtone Cepheids
in the bar of the Large Magellanic Cloud.
    Beaulieu J.P., Grison P., Tobin W., Pritchard J.D., Ferlet R.,
    Lepeintre F., Vidal-Madjar A., Maurice E., Prevot L., Gry C.,
    Guibert J., Moreau O., Tajhamady F., Aubourg E., Bareyre P.,
    Coutures C., Gros M., Laurent B., Lachieze-Rey M., Lesquoy E.,
    Magneville C., Milsztajn A., Moscoso L., Queinnec F., Renault C.,
    Rich J., Spiro M., Vigroux L., Zylberajch S., Ansari R.,
    Cavalier F., Moniez M.
   <Astron. Astrophys. 303, 137 (1995)>
   =1995A&A...303..137B (SIMBAD/NED BibCode)
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ADC_Keywords: Magellanic Clouds; Stars, variable; 
Keywords: surveys - Cepheids - Magellanic Clouds

Description:
    We present CCD phase-binned light curves at 490nm for 97 Cepheid
    variable stars in the bar of the LMC. The photometry was obtained as
    part of the French EROS project and has excellent phase coverage,
    permitting accurate decomposition into Fourier components. We identify
    as `sinusoidal' or s-Cepheids those stars with periods less than 5.5d
    and small second-harmonic components. These stars comprise ~30% of our
    sample and most form a sequence ~1mag brighter than the LMC classical
    Cepheids in the period-luminosity diagram. They are also generally
    bluer and have lower-amplitude light curves. We infer that the
    s-Cepheids are first-overtone pulsators because, when their periods
    are converted to expected fundamental-mode values, they obey a common
    period-luminosity-colour relation with classical Cepheids. This also
    confirms the reality of the colour term in the Cepheid
    period-luminosity-colour relation. Further, the blue edge of the
    classical Cepheid instability strip agrees well with the theoretical
    calculations for the fundamental mode made by Chiosi et al. 1993
    (=1993ApJS...86..541C) for the Hertzsprung-Russell and period-luminosity
    diagrams, but we find that our observed s-Cepheids are >0.2mag brighter
    and bluer than the Chiosi et al. predictions for the first-overtone.
    We identify a number of features in plots of our stars' Fourier-component
    amplitude ratios and phase differences. These features have been identified
    with resonances between different pulsation modes. In the LMC we find these
    features seem to occur at periods very similar to Galactic ones for
    classical Cepheids, but at different periods for s-Cepheids. We
    discover a double-mode Cepheid in the LMC, for which P(first
    overtone)/P(fundamental)=0.710+/-0.001, very similar to observed
    ratios for Galactic double-mode Cepheids.

File Summary:
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  FileName   Lrecl  Records   Explanations
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ReadMe          80        .   This file
table1.dat     137       97   97 LMC bar Cepheids
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Byte-by-byte Description of file: table1.dat
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   Bytes Format Units   Label     Explanations
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   2-  5  I4    ---     EROS      EROS number
   7- 11  I5    ---     HV        ? HV number (Harvard Variable)
      13  I1    h       RAh       Right ascension (J2000)
  15- 16  I2    min     RAm       Right ascension (J2000)
  18- 21  F4.1  s       RAs       Right ascension (J2000)
      23  A1    ---     DE-       Declination sign
  24- 25  I2    deg     DEd       Declination (J2000)
  27- 28  I2    arcmin  DEm       Declination (J2000)
  30- 31  I2    arcsec  DEs       Declination (J2000)
  33- 39  F7.4  d       P         Period
      41  A1    ---     Type      See Note (1)
  43- 47  F5.2  mag     BE        B_E_ magnitude
  49- 53  F5.2  mag     RE        R_E_ magnitude
  55- 59  F5.3  ---     R2/1      Ratio of second harmonic; see note (2)
  61- 65  F5.3  ---     R3/1      ? Ratio of third harmonic; see note (2)
  67- 70  F4.2  ---     Phi2/1    ? Phase difference; see note (3)
  72- 75  F4.2  ---     Phi3/1    ? Phase difference; see note (3)
  78- 81  F4.2  mag   e_BE        Error on BE magnitude
  84- 87  F4.2  mag   e_RE        Error on RE magnitude
  89- 93  F5.3  ---   e_R2/1      Error on R2/1 parameter
  95- 99  F5.3  ---   e_R3/1      ? Error on R3/1 parameter
 101-104  F4.2  ---   e_Phi2/1    Error on phase difference Phi2/1
 106-109  F4.2  ---   e_Phi3/1    ? Error on phase difference Phi3/1
 111-137  A27   ---     Remarks   Remarks
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Note (1): A: Classical light curves
          B: s-Cepheids
          C: anomalous types
          D: double mode Cepheids
          E: intermediate objects in the R_21_-P plane
Note (2): Observed magnitude are decomposed in Fourier with
          X = X0 + X1 cos( (2{pi}/P)(t-t_0_) + Phi1) + ...
                 + Xk cos(k(2{pi}/P)(t-t_0_) + Phik) + ...
          Ratios are defined by
          Rk/1 = Xk/X1              (k>1)
Note (3): Phase differences are defined by
          Phik/1 = Phik - k . Phi1  (k>1)
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(End)                                           Simona Mei [CDS]  07-Dec-1995