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J/A+A/534/A95       LMC Cepheids radial velocities           (Storm+, 2011)

Calibrating the Cepheid period-luminosity relation from the infrared surface brightness technique. II. The effect of metallicity, and the distance to the LMC. Storm J., Gieren W., Fouque P., Barnes T.G., Soszynski I., Pietrzynski G., Nardetto N., Queloz D. <Astron. Astrophys. 534, A95 (2011)> =2011A&A...534A..95S
ADC_Keywords: Magellanic Clouds ; Stars, variable ; Stars, distances; Radial velocities Keywords: stars: variable: Cepheids - stars: fundamental parameters - stars: distances - Magellanic Clouds - distance scale Abstract: The extragalactic distance scale builds directly on the Cepheid Period-Luminosity (PL) relation as delineated by the sample of Cepheids in the Large Magellanic Cloud (LMC). However, the LMC is a dwarf irregular galaxy, quite different from the massive spiral galaxies used for calibrating the extragalactic distance scale. Recent investigations suggest that not only the zero-point but also the slope of the Milky Way PL relation differ significantly from that of the LMC, casting doubts on the universality of the Cepheid PL relation. We want to make a differential comparison of the PL relations in the two galaxies by delineating the PL relations using the same method, the infrared surface brightness method (IRSB), and the same precepts. The IRSB method is a Baade-Wesselink type method to determine individual distances to Cepheids. We apply a newly revised calibration of the method as described in an accompanying paper (Paper I, Cat. J/A+A/534/A94) to 36 LMC and five SMC Cepheids and delineate new PL relations in the V,I,J, & K bands as well as in the Wesenheit indices in the optical and near-IR. We present 509 new and accurate radial velocity measurements for a sample of 22 LMC Cepheids, enlarging our earlier sample of 14 stars to include 36 LMC Cepheids. The new calibration of the IRSB method is directly tied to the recent HST parallax measurements to ten Milky Way Cepheids, and we find a LMC barycenter distance modulus of 18.45±0.04 (random error only) from the 36 individual LMC Cepheid distances. In the J,K bands we find identical slopes for the LMC and Milky Way PL relations and only a weak metallicity effect on the zero points (consistent with a zero effect), metal poor stars being fainter. In the optical we find the Milky Way slopes are slightly shallower than the LMC slopes (but again consistent with no difference in the slopes) and small effects on the zero points. However, the important Wesenheit index in V,(V-I) shows a metallicity effect on the slope and on the zero point which is likely to be significant. We find a significant metallicity effect on the Wvi index gamma(Wvi)=-0.23±0.10mag/dex as well as an effect on the slope. The K-band PL relation on the other hand is found to be an excellent extragalactic standard candle being metallicity insensitive in both slope and zero-point and at the same time being reddening insensitive and showing the least internal dispersion. Description: We present 509 high precision radial velocity measurements for a total of 22 LMC Cepheids obtained with the HARPS spectrograph at the ESO 3.6m telescope, and the FEROS spectrograph on the ESO/MPG 2.2m telescope both at La Silla, Chile. From these data radial velocity curves with good phase coverage can be established. The Cepheids have pulsational periods ranging from about 5 to 80 days. The Cepheids are: HV873, HV876, HV877, HV878, HV881, HV900, HV914, HV1005, HV1006, HV1023, HV2282, HV2369, HV2405, HV2527, HV2538, HV2549, HV5655, HV6093, HV12452, HV12505, HV12717, U1 (= EV* LMC V0033). File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table3.dat 98 36 Distances and absolute magnitudes for the LMC Cepheids calculated using the precepts given in Paper I (2011A&A...534A..95S), using the new p-factor relation table2.dat 28 509 Time stamps and radial velocities
See also: J/A+A/534/A94 : Milky Cepheids radial velocities (Storm+, 2011) Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 7 A7 --- Name Star name 9- 16 F8.6 [d] logP Period 18- 21 F4.1 kpc d Near-IR surface brightness (IRSB) distance 23- 25 F3.1 kpc e_d rms uncertainty on d 27- 31 F5.2 mag (m-M)0 Distance modulus 33- 36 F4.2 mag e_(m-M)0 rms uncertainty on (m-M)0 38- 42 F5.2 mag VMAG Absolute V magnitude 44- 48 F5.2 mag IMAG ?=- Absolute I magnitude 50- 54 F5.2 mag JMAG Absolute J magnitude 56- 60 F5.2 mag HMAG ?=- Absolute H magnitude 62- 66 F5.2 mag KMAG Absolute K magnitude 68- 72 F5.2 mag WVI ?=- Wesenheits reddening-free WVI_ index (WVI=I-2.55(V-I)) 74- 78 F5.2 mag WJK Wesenheits reddening-free WJK index (WJK=Ks-0.686(J-Ks )) 80- 84 F5.3 mag E(B-V) Adopted reddening 86- 91 F6.3 --- Dphi Adopted phase shift between spectroscopic and photometric angular diameters 93- 98 F6.3 mag d(m-M) Magnitude correction to refer the distance moduli to the LMC barycenter
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 7 A7 --- Name Variable star identifier 10- 21 F12.4 d HJD Heliocentric Julian Date 23- 28 F6.2 km/s HRV Heliocentric Radial Velocity
Acknowledgements: Jesper Storm, jstorm(at) References: Storm et al., Paper II 2011A&A...534A..94S, Cat. J/A+A/534/A94
(End) Jesper Storm [AIP, Germany], Patricia Vannier [CDS] 07-Oct-2011
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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