SCYON Abstract

Received on January 1 2007

The Distances to Open Clusters from Main-Sequence Fitting. III. Improved Accuracy with Empirically Calibrated Isochrones

AuthorsDeokkeun An (1), Donald M. Terndrup (1), Marc H. Pinsonneault (1), Diane B. Paulson (2), Robert B. Hanson (3), and John R. Stauffer (4)
Affiliation
(1) The Ohio State University
(2) NASA/GSFC
(3) UCO/Lick Observatory
(4) IPAC/Caltech
Accepted byAstrophysical Journal
Contactdeokkeun@astronomy.ohio-state.edu
URLhttp://www.astronomy.ohio-state.edu/iso/
Links Praesepe / Pleiades / M67 / NGC 2516

Abstract

We continue our series of papers on open cluster distances with a critical assessment of the accuracy of main-sequence fitting using isochrones which employ empirical corrections to the color-temperature relations. We use four nearby open clusters with multicolor photometry and accurate metallicities, and present a new metallicity for Praesepe ([Fe/H] = +0.11 +/- 0.03) from high-resolution spectra. The internal precision of distance estimates is about a factor of five better than the case without the color calibrations. After taking into account all major systematic errors, we obtain distances accurate to about 2-3% when there exists a good metallicity estimate. Metallicities accurate to better than 0.1 dex may be obtained from BVICKs photometry alone. We also derive a helium abundance for the Pleiades of Y = 0.279 +/- 0.015, which is equal within the errors to the Sun's initial helium abundance and that of the Hyades. Our best estimates of distances are (m - M)0 = 6.33 +/- 0.04, 8.03 +/- 0.04, and 9.61 +/- 0.03 to Praesepe, NGC 2516, and M67, respectively. Our Pleiades distance at the spectroscopic metallicity, (m - M)0 = 5.66 +/- 0.01 (internal) +/- 0.05 (systematic), is in excellent agreement with several geometric distance measurements. We have made calibrated isochrones for -0.3 <= [Fe/H] <= +0.2 available online.