RR Lyrae stars and the horizontal branch of NGC 5904 (M5)

Abstract

We report the distance and [Fe/H] value for the globular cluster NGC 5904 (M5) derived from the Fourier decomposition of the light curves of selected RRab and RRc stars. The aim in doing this was to bring these parameters into the homogeneous scales established by our previous work on numerous other globular clusters, allowing a direct comparison of the horizontal branch luminosity in clusters with a wide range of metallicities. Our CCD photometry of the large variable star population of this cluster is used to discuss light curve peculiarities, like Blazhko modulations, on an individual basis. New Blazhko variables are reported.From the RRab stars we found [Fe/H] UVES = −1.335 ± 0.003(statistical) ± 0.110(systematic), and a distance of 7.6 ± 0.2 kpc, and from the RRc stars we found [Fe/H] UVES = −1.39 ± 0.03(statistical) ± 0.12(systematic) and a distance of 7.5 ± 0.3 kpc. The results for RRab and RRc stars should be considered independent since they come from different calibrations and zero points. Absolute magnitudes, radii and masses are also reported for individual RR Lyrae stars. The distance to the cluster was also calculated by alternative methods like the Period-Luminosity relation of SX Phe and the luminosity of the stars at the tip of the red giant branch, and we obtained the results 7.7 ± 0.4 and 7.2 − 7.5 kpc respectively.The distribution of RR Lyrae stars in the instability strip is discussed and compared with other clusters in connection with the Oosterhoff and horizontal branch type. The Oosterhoff type II clusters systematically show a RRab-RRc segregation about the instability strip first-overtone red edge, while the Oosterhoff type I clusters may or may not display this feature. A group of RR Lyrae stars is identified in an advanced evolutionary stage, and two of them are likely binaries with unseen companions.

Absolute Magnitudes and Colors of RR Lyrae Stars in DECam Passbands from Photometry of the Globular Cluster M5

“…We took advantage of the fact that the variable stars in M5 have been extensively studied before and adopted in several cases the published periods in the catalog of Clement et al (2001), which in the case of M5 had an update 8 in 2015 June. A recent revision of variable stars in M5 is also provided by Arellano Ferro et al (2016). Each light curve was fitted with a template from the library of Sesar et al (2010) that was created from SDSS ugriz observations of RR Lyrae stars in Stripe 82.…”

“…The colors for this star are too red to be an RRc. Arellano Ferro et al (2016) flagged this star (V85 in their nomenclature) as a Blazhko star, but their light curve looks clearly like an RRab. Thus, it may be a case of extreme Blazhko effect or mode changing.…”

Blazhko effect in the Galactic bulge fundamental mode RR Lyrae stars – II. Modulation shapes, amplitudes, and periods

“…Is the occurrence of the modulation driven by some particular physical property (e.g. temperature, chemical composition, Jurcsik et al 2011;Arellano Ferro et al 2016a)? Why is the occurrence of modulated RRLs lower among stars with longer pulsation periods (Jurcsik et al 2011;Skarka 2014)?…”

Metallicity and distance of NGC 6362 from its RR Lyrae and SX Phoenicis stars

“…The method, originally developed to estimate distances to nearby galaxies (Lee et al ), has been used to corroborate the theoretical constrains that particle physics may impose on the extension of the RGB in globular clusters by comparing the predicted distance by the most luminous RGB with the results rendered by the RR Lyrae and SX Phe. Consistency between theoretical predictions and empirical calculations has been found for NGC 6229 by Arellano Ferro et al (), for M5 by Arellano Ferro et al (), and for NGC 6934 by Yepez et al . In brief, the bolometric absolute magnitude of the tip of the RGB was calibrated by Salaris & Cassisi () as: where [ M / H ] = [Fe/H] − log(0.638 f + 0.362), and log f = [ α /Fe], Salaris et al ().…”

“…The isochrone for 12.1 Gyr, [Fe/H] = −1.0, Y = 0.25 and [ α /H] = 0.4, and the slightly more metal poor zahb (−1.31) are from VandenBerg et al () and have been reddened by E ( B − V ) = 0.063 and shifted to the average distance modulus found from the RRL stars. The vertical black line shows the first overtone red edge calculated by Arellano Ferro et al () and shows the neat mode segregation…”