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

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 2MASS (J − K S ) CMDs, using the τ 2 maximum-likelihood procedure of Naylor (2009), and an alternative method using 2D cross-correlations developed in this work. We find best fits for 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 by 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.

Proper motions of the optically visible open clusters based on the UCAC4 catalog

“…For the other 9 clusters with very different mean proper motion (Alessi 13, Melotte 20, Stock 2, ASCC 13, Platais 2, IC 2602, NGC 2541A, Mamajek 1, Platais 10), our analysis was unable to distinguish between members and background stars due to the large size of the clusters. For these cases, an analysis based on photometric and spectroscopic data becomes crucial, as presented by Curtis et al (2013) for the open cluster Ruprecht 147.…”

EPIC 219388192b—An Inhabitant of the Brown Dwarf Desert in the Ruprecht 147 Open Cluster

“…The uniqueness of EPIC 219388192b stems from the fact that the host star is a member of the Ruprecht 147 cluster (Curtis et al 2013), providing a robust age determination. Based on the spectroscopic, as well as near-infrared and optical photometric isochrone fitting to the Dartmouth (Dotter et al 2008) 26 and PARSEC (Bressan et al 2012) 27 stellar evolution models, Curtis et al (2013) determined an age of 2.75-3.25 Gyr for the Ruprecht 147 cluster.…”

“…The uniqueness of EPIC 219388192b stems from the fact that the host star is a member of the Ruprecht 147 cluster (Curtis et al 2013), providing a robust age determination. Based on the spectroscopic, as well as near-infrared and optical photometric isochrone fitting to the Dartmouth (Dotter et al 2008) 26 and PARSEC (Bressan et al 2012) 27 stellar evolution models, Curtis et al (2013) determined an age of 2.75-3.25 Gyr for the Ruprecht 147 cluster. Thus, EPIC 219388192b plays a very important role in the verification of the BD evolutionary models (Burrows et al 1993(Burrows et al , 1997(Burrows et al , 2006(Burrows et al , 2011Chabrier et al 2000;Baraffe et al 2003;Saumon & Marley 2008).…”

ROTATIONAL AND RADIAL VELOCITIES OF 1.3-2.2M☉RED GIANTS IN OPEN CLUSTERS

“…They identify 11 stars as RG stars in the g versus g − i CMD, which were targeted in this study. The RG stars successfully observed are CWWID 1, 2, 6, 9, 11, 15, and 19 (Curtis et al 2013), as well as CWWID 7 (accidentally added to the list, but it had the right Two Micron Sky Survey (2MASS) colors for an RG star). In this study, the numbering system comes from Kharchenko et al (2005).…”