Physical parameter determination of seven RR Lyrae stars in Bootes

Abstract

uvby β photoelectric photometry of the RR Lyrae stars AE, RS, ST, TV, TW, UU, and XX Bootis has been acquired in order to determine the physical parameters of the stars. We used the correlation between the Fourier parameters derived from the light curves and the physical parameters such as the absolute magnitude Mv , intrinsic colour (B − V ) 0 and metal abundance [Fe/H]. Once reddening has been determined, unreddened indices are obtained and T eff and log g followed along the cycle, using a comparison with the theoretical models given for our determined metallicity. AnalysisOur knowledge on stellar evolution comes from a direct comparison between the observational determination of the star's basic physical parameters (i.e. T eff , g , luminosity, metallicity and eventual pulsation periods) and models. In the case of the RR Lyrae variables, some of the goals can be attained from the relationships that have been developed by Kovács & Jurcsik in several papers , 1997, Jurcsik 1998. As Kovács & Walker (2001) state in their review paper, this method is empirical and based on the assumption that the period and the shape of the light curve are directly correlated with the physical parameters. Since we have obtained simultaneous uvby β photoelectric photometry, the precise variation of these parameters along the cycle can be determined for each star.The observations were all taken at the Observatorio Astronómico Nacional, Mexico. The 1.5m telescope, to which a spectrophotometer was attached, was used in all seasons. The physical parameters can be determined with the ad-hoc models. From the data of several photometric campaigns we obtained uvby β photometry, which was used to calculate the physical parameters of each star. The fit with our observations has been considered as reasonable when the rms error is the same order of magnitude as the detected amplitude. Reddening has been estimated by considering different objects in the same direction. Once reddening has been fixed, the unreddened Strömgren indices give the variation along the cycle of the effective temperature and surface gravity. These results are summarized in Table 1 which reports the physical parameters. The last two columns list the number of data points and the standard deviation of the residuals.Acknowledgments. This paper was partially supported by Papiit IN108106. This article has made use of the SIMBAD database operated at CDS, Strasbourg, France and ADS, NASA Astrophysics Data Systems hosted by Harvard-Smithsonian Center for Astrophysics.

A far-ultraviolet variability survey of the globular cluster M 80

“…RR Lyrae stars are horizontal branch (HB) stars with T eff about 6000-7600 K and radii between 4 and 7 R (e.g. Smith 1995;Lázaro et al 2006;Peña et al 2008;Sódor et al 2009), which exhibit periodic variability with amplitude 0.2-2 mag at optical wavelengths and up to 8 mag at UV wavelengths (Wheatley et al 2005). The variability is well understood to be due to radial pulsations that result in radius and effective temperature changes.…”

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

“…A number of studies have made use of these empirical relations to derive the physical parameters of the RRL stars. To list a few of these studies, Kaluzny et al (2000) used these empirical relations to estimate physical parameters of 26 RRab and 16 RRc stars in M5, Peña et al (2007) used these empirical relations to estimate physical parameters of seven RRL stars in Bootes and Arellano Ferro et al (2008) have determined parameters for few RRL variables in NGC 5466. There are a number of other studies that have made use of the Fourier coefficients to determine various parameters of astrophysical importance.…”