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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 A. Johnson
; | | Date: |
28 Jun 2012 | | 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 candidate blue
stragglers, 11 red giants, and 5 SB2 binaries. We estimate the cluster
metallicity from spectroscopic analysis, using Spectroscopy Made Easy (SME),
and find it to be [M/H] = +0.08 pm 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) CMDs, using the au^2 maximum-likelihood procedure of Naylor (2009). We
find best fits for isochrones at age t = 2.5 pm 0.25 Gyr, m pm M = 7.35 pm
0.1, and A_V = 0.25 pm 0.05, with significant uncertainty from the unresolved
binary population and possibility of differential extinction across this large
cluster. Our preferred model does not simultaneously fit the main sequence
turnoff and the red giant branch in the optical CMD. We investigate alternative
solutions and find that an older, closer and less extinguished Padova model
with age t = 3.5 Gyr, m - M = 7.0, and A_V = 0.10 appears to better match the
overall optical CMD (particularly the red giant branch). We do not favor this
model because it poorly fits the upper main sequence in the optical, the age is
inconsistent with our spectroscpic results, and our preferred model better fits
the NIR CMD. Still, we cannot yet conclusively rule out the older solution. At
250 - 300 pc and an age of 2.5 - 3.5 Gyr, Ruprecht 147 is by far the oldest
nearby star cluster. | | Source: | arXiv, 1206.6533 | | Services: | Forum | Review | PDF | Favorites | |
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