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J/A+A/303/137       EROS Variables: Cepheids in the bar of LMC  (Beaulieu+ 1995)

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)
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:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 137 97 97 LMC bar Cepheids
Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
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 BE magnitude 49- 53 F5.2 mag RE RE 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
Note (1): A: Classical light curves B: s-Cepheids C: anomalous types D: double mode Cepheids E: intermediate objects in the R21-P plane Note (2): Observed magnitude are decomposed in Fourier with X = X0 + X1 cos( (2π/P)(t-t0) + Phi1) + ... + Xk cos(k(2π/P)(t-t0) + 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)

(End) Simona Mei [CDS] 07-Dec-1995
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