Ruprecht 147: The Oldest Nearby Open Cluster as a New Benchmark for Stellar Astrophysics

Creators: Curtis, Jason L.; Wolfgang, Angie; Wright, Jason T.; Brewer, John M.; Johnson, John Asher

Abstract

Ruprecht 147 is a hitherto unappreciated open cluster that holds great promise as a standard in fundamental stellar astrophysics. We have conducted a radial velocity survey of astrometric candidates with Lick, Palomar, and MMT observatories and have identified over 100 members, including 5 blue stragglers, 11 red giants, and 5 double-lined spectroscopic binaries (SB2s). We estimate the cluster metallicity from spectroscopic analysis, using Spectroscopy Made Easy (SME), and find it to be [M/H] = +0.07 ± 0.03. We have obtained deep CFHT/MegaCam g'r'i'z' photometry and fit Padova isochrones to the (g' – i') and Two Micron All Sky Survey (J – K_S ) color-magnitude diagrams, using the τ^2 maximum-likelihood procedure of Naylor, and an alternative method using two-dimensional cross-correlations developed in this work. We find best fits for Padova isochrones at age t = 2.5 ± 0.25 Gyr, m – M = 7.35 ± 0.1, and A_V = 0.25 ± 0.05, with additional uncertainty from the unresolved binary population and possibility of differential extinction across this large cluster. The inferred age is heavily dependent on our choice of stellar evolution model: fitting Dartmouth and PARSEC models yield age parameters of 3 Gyr and 3.25 Gyr, respectively. At ~300 pc and ~3 Gyr, Ruprecht 147 is by far the oldest nearby star cluster.

Additional Information

© 2013 American Astronomical Society. Received 2012 May 26; accepted 2012 December 7; published 2013 April 4. J.L.C. acknowledges support from the National Science Foundation Graduate Research Fellowship Program supported by NSF grant No. DGE1255832, NSF grant No. AST-1211785 (PI: J.T.W.), the Stephen B. Brumbach graduate fellowship, and the Zaccheus Daniel travel grant program. A.W. acknowledges a Hunter R. Rawlings III Cornell Presidential Research Scholarship. J.T.W. conceived of and oversaw the project, and collected all of the candidate stellar spectra. A.W. and J.T.W. conducted the radial velocity survey at Palomar and Lick and produced the preliminary R147 membership list. J.M.B. conducted the SME analysis. J.A.J. was PI on the program that obtained the optical photometry from CFHT/MegaCam, and also conducted preliminary SME analysis of Lick andKeck spectra to determine the composition of R147 (results are not reported in this work, though they informed this study). J.L.C. and J.T.W. performed the Hectochelle RV survey. J.L.C. was primarily responsible for the writing of the manuscript and the final analysis and synthesis of all data. We would like to thank Gabor Füurész and Andrew Szentgyorgyi for assisting the Hectochelle data reduction; Tim Naylor for assisting us with his τ 2 code; Aaron Dotter for providing access to the Dartmouth isochrones with the CFHT/MegaCam filters; David Monet and Stephen Levine for providing the NOMAD catalog on HDD; James Graham and James Lloyd for supporting this research; Matthew Muterspaugh for sharing and swapping Lick 3 m time; and Kevin Covey for providing extensive comments on an early draft of this paper. We would also like to thank all observing staff and telescope operators at MMT/FLWO, CFHT, Lick, Palomar, and Keck; and Geoff Marcy, Andrew Howard and the California Planet Survey observing team for their assistance in acquiring the Keck spectra. We also appreciate the anonymous referee for offering thorough and constructive suggestions that improved this paper. Finally, we thank Debra Fischer, Jeff Valenti, Adam Kraus, Steve Saar, Søren Meibom, Andrew West, Kevin Covey, Marcel Agüeros, Suzanne Hawley, Ivan King, Jay Anderson, Bob Mathieu, Ken Janes, and Eric Mamajek for helpful conversations, suggestions, and support. This work is based on observations obtained with Mega-Cam, a joint project of CFHT and CEA/DAPNIA, at the Canada–France–Hawaii Telescope (CFHT), which is operated by the National Research Council (NRC) of Canada, the Institute National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. Observing timewas granted by theUniversity of Hawaii Institute for Astronomy TAC. These data were reduced at the TERAPIX data center located at the Institut d'Astrophysique de Paris. Observations reported here were obtained at the MMT Observatory, a joint facility of the Smithsonian Institution and the University of Arizona. MMT telescope time was granted by NOAO (Project PA-10A-0378; PI: J.Wright), through the Telescope System Instrumentation Program (TSIP). TSIP is funded by NSF. 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 NASA and the NSF. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This research made use of Montage, funded by NASA's Earth Science Technology Office, Computation Technologies Project, under Cooperative Agreement Number NCC5-626 between NASA and the California Institute of Technology. Montage is maintained by the NASA/IPAC Infrared Science Archive. This research made use of the WEBDA database operated at the Institute for Astronomy of the University of Vienna, NASA's Astrophysics Data System Bibliographic Services, and the SIMBAD database and the VizieR catalog access tool operated at CDS, Strasbourg, France. The Center for Exoplanets and Habitable Worlds is Supported by The Pennsylvania State University, the Eberly College of Science, and the Pennsylvania Space Grant Consortium. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation or any other institute cited above. Facilities: Shane, Hale, MMT, CFHT, Keck:I

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