Ruprecht 147: The oldest nearby open cluster as a new benchmark for stellar astrophysics

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

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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 τ2 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 AV = 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.

Original languageEnglish (US)
Article number134
JournalAstronomical Journal
Issue number5
StatePublished - May 2013

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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