J/A+A/440/487 Cepheids in the young LMC cluster NGC 1866 (Storm+, 2005)
The near-IR Surface Brightness Method applied to six Cepheids in the young
LMC cluster NGC 1866.
Storm J., Gieren W.P., Barnes III T.G., Gomez, M.
<Astron. Astrophys. 440, 487 (2005)>
=2005A&A...440..487S 2005A&A...440..487S
ADC_Keywords: Magellanic Clouds ; Clusters, globular ; Stars, variable ;
Photometry, infrared ; Radial velocities
Keywords: stars: variables: Cepheids - galaxies: Magellanic Clouds -
stars: distances - stars: fundamental parameters -
galaxies: distances and redshifts
Abstract:
We present new near-IR light curves for six Cepheids in the young blue
LMC cluster NGC 1866 as well as high precision radial velocity curves
for ten Cepheids in NGC 1866 and two in NGC 2031. For the six Cepheids
in NGC 1866 with new J and K light curves we determine distances and
absolute magnitudes by applying the near-IR surface brightness method.
We find that the formal error estimates on the derived distances are
underestimated by about a factor of two. We find excellent agreement
between the absolute magnitudes for the low metallicity LMC Cepheids
with the Period-Luminosity (P-L) relation determined by the near-IR
surface brightness (ISB) method for Galactic Cepheids suggesting that
the slope of the P-L relations for low metallicity and solar
metallicity samples could be very similar in contrast to other recent
findings. Still there appears to be significant disagreement between
the observed slopes of the OGLE based apparent P-L relations in the
LMC and the slopes derived from ISB analysis of Galactic Cepheids, and
by inference for Magellanic Cloud Cepheids, indicating a possible
intrinsic problem with the ISB method itself. Resolving this problem
could reaffirm the P-L relation as the prime distance indicator
applicable as well to metallicities significantly different from the
LMC value.
Description:
Near-infrared photometric light (K-band) and color (J-K) curves are
presented for six Cepheids the Large Magellanic Cloud cluster NGC 1866
in Table 1. Barycentric velocity curves for these stars as well as for
four additional cluster Cepheids and two Cepheids in the LMC cluster
NGC 2031 are presented in Table 2. The systemic (gamma) velocities for
these stars are presented in table 4.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 56 326 K and (J-K) photometric time series for the
NGC 1866 Cepheids
table2.dat 40 137 Radial velocity time series for the NGC 1866 and
NGC 2031 Cepheids
table4.dat 20 12 Systemic velocities for the LMC 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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1- 12 A12 --- Name Star designation
14- 26 F13.5 d HJD Heliocentric Julian Date
29- 34 F6.3 mag Kmag K magnitude
37- 41 F5.3 mag e_Kmag rms uncertainty on K magnitude
45- 49 F5.3 mag J-K (J-K) color index
52- 56 F5.3 mag e_J-K rms uncertainty on (J-K) color index
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 12 A12 --- Name Star designation
18- 29 F12.4 d HJD Heliocentric Julian Date
31- 34 F4.2 --- Phase Phase
36- 40 F5.1 km/s BRV Barycentric radial velocity
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 12 A12 --- Name Star designation
14- 18 F5.1 km/s BRV Barycentric phase averaged radial velocity
20 A1 --- Flag [a] "a" indicates stars with suspected
orbital motion
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Acknowledgements: J. Storm, jstorm(at)aip.de,
Astrophysikalisches Institut Potsdam
(End) Patricia Vannier [CDS] 10-Jun-2005