On the Distance of the Globular Cluster M4 (NGC 6121) Using RR Lyrae Stars. II. Mid-infrared Period-luminosity Relations
Journal
Date Issued
2015
Author(s)
Neeley, J. R.
•
Marengo, M.
•
Bono, G.
•
•
•
Stetson, P. B.
•
Buonanno, R.
•
Ferraro, I.
•
Freedman, W. L.
•
Iannicola, G.
•
Madore, B. F.
•
Matsunaga, N.
•
Monson, A.
•
Persson, S. E.
•
Scowcroft, V.
•
Seibert, M.
Description
We thank the anonymous referee for providing constructive comments that improved the content of this paper. This work is based [in part] on observations made with the Spitzer Space Telescope , which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. 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). Facilities: Spitzer (IRAC) .
Abstract
New mid-infrared (MIR) period-luminosity (PL) relations are presented for RR Lyræ variables in the globular cluster M4 (NGC 6121). Accurate photometry was obtained for 37 RR Lyræ variables using observations from the Infrared Array Camera on board the Spitzer Space Telescope. The dispersion of M4's PL relations is 0.056, and the uncertainty in the slope is 0.11 mag. Additionally, we established calibrated PL relations at 3.6 and 4.5 μm using published Hubble Space Telescope geometric parallaxes of five Galactic RR Lyræ stars. The resulting band-averaged distance modulus for M4 is μ =11.399+/- 0.007({stat}) ± 0.080({syst}) ± 0.015({cal})+/- 0.020({ext}). The systematic uncertainty will be greatly reduced when parallaxes of more stars become available from the GAIA mission. Optical and infrared period-color (PC) relations are also presented, and the lack of an MIR PC relation suggests that RR Lyræ stars are not affected by CO absorption in the 4.5 μm band.
Volume
808
Issue
1
Start page
11
Issn Identifier
0004-637X
Ads BibCode
2015ApJ...808...11N
Rights
open.access
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