Please use this identifier to cite or link to this item:
|Title:||On the Distance of the Globular Cluster M4 (NGC 6121) Using RR Lyrae Stars. I. Optical and Near-infrared Period-Luminosity and Period-Wesenheit Relations||Authors:||Braga, Vittorio Francesco
Stetson, P. B.
Persson, S. E.
Madore, B. F.
|Issue Date:||2015||Journal:||THE ASTROPHYSICAL JOURNAL||Number:||799||Issue:||2||First Page:||165||Abstract:||We present new distance determinations to the nearby globular M4 (NGC 6121) based on accurate optical and near-infrared (NIR) mean magnitudes for fundamental (FU) and first overtone (FO) RR Lyrae variables (RRLs), and new empirical optical and NIR period-luminosity (PL) and period-Wesenheit (PW) relations. We have found that optical-NIR and NIR PL and PW relations are affected by smaller standard deviations than optical relations. The difference is the consequence of a steady decrease in the intrinsic spread of cluster RRL apparent magnitudes at fixed period as longer wavelengths are considered. The weighted mean visual apparent magnitude of 44 cluster RRLs is <V > =13.329 ± 0.001 (standard error of the mean) ±0.177 (weighted standard deviation) mag. Distances were estimated using RR Lyr itself to fix the zero-point of the empirical PL and PW relations. Using the entire sample (FU+FO) we found weighted mean true distance moduli of 11.35 ± 0.03 ± 0.05 mag and 11.32 ± 0.02 ± 0.07 mag. Distances were also evaluated using predicted metallicity dependent PLZ and PWZ relations. We found weighted mean true distance moduli of 11.283 ± 0.010 ± 0.018 mag (NIR PLZ) and 11.272 ± 0.005 ± 0.019 mag (optical-NIR and NIR PWZ). The above weighted mean true distance moduli agree within 1σ. The same result is found from distances based on PWZ relations in which the color index is independent of the adopted magnitude (11.272 ± 0.004 ± 0.013 mag). These distances agree quite well with the geometric distance provided by Kaluzny et al. based on three eclipsing binaries. The available evidence indicates that this approach can provide distances to globulars hosting RRLs with a precision better than 2%-3%.||Acknowledgments:||It is a pleasure to thank the organizers of the MIAPP–Munich Institute for Astro and Particle Physics–workshop on The Extragalactic Distance Scale. During the workshop several authors have had the opportunity to present the preliminary results of this investigation and to discuss pros and cons of the RR Lyrae distance scale in a very fruitful and pleasant environment. In addition we warmly thank R.P. Kudritzski for many useful discussions and insights concerning stellar atmospheres and non-LTE effects in giant stars. We also would like to thank an anonymous referee for several suggestions concerning the content and the cut of an early version of the current manuscript. This work was partially supported by PRIN–INAF 2011 “Tracing the formation and evolution of the Galactic halo with VST” (P.I.: M. Marconi) and by PRIN–MIUR (2010LY5N2T) “Chemical and dynamical evolution of the Milky Way and Local Group galaxies” (P.I.: F. Matteucci). One of us (G.B.) thanks The Carnegie Observatories visitor programme for support as science visitor. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.||URI:||http://hdl.handle.net/20.500.12386/24113||URL:||https://iopscience.iop.org/article/10.1088/0004-637X/799/2/165||ISSN:||0004-637X||DOI:||10.1088/0004-637X/799/2/165||Bibcode ADS:||2015ApJ...799..165B||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
Show full item record
Files in This Item:
|Braga_2015_ApJ_799_165.pdf||PDF editoriale||1.03 MB||Adobe PDF||View/Open|
checked on Sep 21, 2020
checked on Sep 21, 2020
Items in DSpace are published in Open Access, unless otherwise indicated.