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 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:
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FileName Lrecl Records Explanations
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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 2011A&A...534A..95S), using the new
p-factor relation
table2.dat 28 509 Time stamps and radial velocities
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See also:
J/A+A/534/A94 : Milky Cepheids radial velocities (Storm+, 2011)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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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
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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- 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
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Acknowledgements:
Jesper Storm, jstorm(at)aip.de
References:
Storm et al., Paper II 2011A&A...534A..94S 2011A&A...534A..94S, Cat. J/A+A/534/A94
(End) Jesper Storm [AIP, Germany], Patricia Vannier [CDS] 07-Oct-2011