A uvbyCaHbeta Analysis of the Old Open Cluster, NGC 6819

Abstract

NGC 6819 is a richly populated, older open cluster situated within the Kepler field. A CCD survey of the cluster on the uvbyCaHbeta system, coupled with proper-motion membership, has been used to isolate 382 highly probable, single-star unevolved main-sequence members over a 20-arcminute field centered on the cluster. From 278 F dwarfs with high precision photometry in all indices, a mean reddening of E(b-y) = 0.117 +/- 0.005 or E(B-V) = 0.160 +/- 0.007 is derived, where the standard errors of the mean include both internal errors and the photometric zero-point uncertainty. With the reddening fixed, the metallicity derived from the same 278 stars is [Fe/H] = -0.116 +/- 0.101 from m_1 and -0.055 +/- 0.033 from hk, for a weighted average of [Fe/H] = -0.06 +/- 0.04, where the quoted standard errors of the mean values include the internal errors from the photometric scatter plus the uncertainty in the photometric zero points. If metallicity is derived using individual reddening values for each star to account for potential reddening variation across the face of the cluster, the analogous result is unchanged. The cluster members at the turnoff of the color-magnitude diagram are used to test and confirm the recently discovered variation in reddening across the face of the cluster, with a probable range in the variation of Delta[E(B-V)] = 0.045 +/-0.015. With the slightly higher reddening and lower [Fe/H] compared to commonly adopted values, isochrone fitting leads to an age of 2.3 +/- 0.2 Gyr for an apparent modulus of (m-M) = 12.40 +/-0.12.

WIYN Open Cluster Study LXI; accepted to Astronomical Journal. 11 figures, 2 tables

References in corpus (4)

• vbyCaHbeta CCD Photometry of Clusters. VIII. The Super-Metal Rich, Old Open Cluster NGC 6791
• Asteroseismic Study on Cluster Distance Moduli for RGB Stars in NGC 6791 and NGC 6819
• uvbyCa H beta CCD Photometry of Clusters. VII. The Intermediate-Age Anticenter Cluster Melotte 71
• NGC 4337: an over-looked old cluster in the inner disc of the Milky Way

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• WIYN Open Cluster Study LXXXV. Li in NGC 2243 -- Implications for Stellar and Galactic Evolution
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• A uvbyCaHbeta CCD Analysis of the Open Cluster Standard, M67,and its Relation to NGC 752
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