Volume 502, Number 2, August I 2009
|Page(s)||505 - 514|
|Published online||15 June 2009|
III. Near-infrared study
Departamento de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Ave. Gran Bretaña 1111, Playa Ancha, Casilla 53, Valparaíso, Chile e-mail: firstname.lastname@example.org
2 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching b. München, Germany e-mail: email@example.com
3 Department of Astronomy, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile e-mail: [dante;mcatelan]@astro.puc.cl
4 Vatican Observatory, V00120 Vatican City State, Italy
5 John Simon Guggenheim Memorial Foundation Fellow
6 On sabbatical leave at Catholic University of America, Department of Physics, 200 Hannan Hall, Washington, DC 20064, USA
7 European Southern Observatory, Av. Alonso de Córdoba 3107, Casilla 19, Santiago 19001, Chile e-mail: firstname.lastname@example.org
Accepted: 21 April 2009
Context. RR Lyrae variable stars are the primary Population II distance indicator. Likewise, the Large Magellanic Cloud (LMC) constitutes a key step in the extragalactic distance scale.
Aims. By combining near-IR photometry and spectroscopically measured metallicities for a homogeneous sample of 50 RR Lyr stars in the LMC, we investigate the metallicity dependence of the period-luminosity relation in the near-infrared (IR), use the newly derived relations to re-derive the distance to the LMC, and compare the distance moduli obtained from RR Lyr and red clump stars.
Methods. This paper presents new (single-epoch) J-band and (multi-epoch) Ks-band photometry of RR Lyr stars in 7 different LMC fields, observed with the near-IR camera SOFI at ESO's New Technology Telescope. Additional Ks-band data for another two LMC fields were taken with the ISPI infrared array at CTIO's Blanco 4m telescope. The near-IR photometry was cross-correlated with the MACHO and OGLE databases, resulting in a catalog of 62 RR Lyr stars with BVRIJKs photometry. A subsample of 50 stars also has spectroscopically measured metallicities.
Results. In the deep JK color–magnitude diagrams of 7 fields, red giant branch, red clump and RR Lyr stars are detected. The majority of RR Lyr stars are located within the instability strip with near-IR colors between . The period-luminosity relation only has a very mild dependence on metallicity in the K band, consistent with no dependence: In the J band the currently available data do not allow firm conclusions regarding the metallicity dependence of the period-luminosity relation.
Conclusions. The distance modulus of the LMC, derived using our near-IR period-luminosity-metallicity relation for RR Lyr stars, is , in very good agreement with the distance modulus from the red clump stars, . However, LMC modulus derived from the RR Lyrae stars depends on the parallax of the star RR Lyrae.
Key words: Galaxies: Magellanic Clouds / stars: variables: RR Lyr / galaxies: distances and redshifts / stars: oscillations
Based on observations collected with European Southern Observatory's Very Large Telescope and New Technology Telescope, under programs 64.N-0176(B), 70.B-0547(A), and 072.D-0106(B) with the Blanco telescope at CTIO, under ISPI Prop. No. 0101; and at Gemini Observatory (observing program GS-2004A-Q-27), which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência e Tecnologia (Brazil), and SECYT (Argentina).
© ESO, 2009
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