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 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 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