Journal Article

Physical parameters of the Small Magellanic Cloud RR Lyrae stars and the distance scale

Sukanta Deb and Harinder P. Singh

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 402, issue 1, pages 691-704
Published in print February 2010 | ISSN: 0035-8711
Published online February 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.15927.x
Physical parameters of the Small Magellanic Cloud RR Lyrae stars and the distance scale

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We present a careful and detailed light curve analysis of RR Lyrae stars in the Small Magellanic Cloud (SMC) discovered by the Optical Gravitational Lensing Experiment (OGLE) project. Out of 536 single-mode RR Lyrae stars selected from the data base, we have investigated the physical properties of 335 ‘normal-looking’ RRab stars and 17 RRc stars that have good quality photometric light curves. We have also been able to estimate the distance modulus of the cloud which is in good agreement with those determined from other independent methods. The Fourier decomposition method has been used to study the basic properties of these variables. Accurate Fourier decomposition parameters of 536 RR Lyrae stars in the OGLE-II data base are computed. Empirical relations between the Fourier parameters and some physical parameters of these variables have been used to estimate the physical parameters for the stars from the Fourier analysis. Further, the Fourier decomposition of the light curves of the SMC RR Lyrae stars yields their mean physical parameters as and MV= 0.78 ± 0.02 for 335 RRab variables and and MV= 0.76 ± 0.05 for 17 RRc stars. Using the absolute magnitude together with the mean magnitude, intensity-weighted mean magnitude and the phase-weighted mean magnitude of the RR Lyrae stars, the mean distance modulus to the SMC is estimated to be 18.86 ± 0.01, 18.83 ± 0.01 and 18.84 ± 0.01 mag, respectively, from the RRab stars. From the RRc stars, the corresponding distance modulus values are found to be 18.92 ± 0.04, 18.89 ± 0.04 and 18.89 ± 0.04 mag, respectively. Since the Fourier analysis is a very powerful tool for the study of the physical properties of the RR Lyrae stars, we emphasize the importance of exploring the reliability of the calculation of Fourier parameters together with the uncertainty estimates keeping in view the large collections of photometric light curves that will become available from variable star projects of the future.

Keywords: methods: data analysis; astronomical data bases: miscellaneous; stars: fundamental parameters; stars: variables: other; Magellanic Clouds

Journal Article.  7329 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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