AGE AND DISTANCE FOR THE OLD OPEN CLUSTER NGC 188 FROM THE ECLIPSING BINARY MEMBER V 12

作者：Meibom Soren^*; Grundahl Frank; Clausen Jens Viggo; Mathieu Robert D; Frandsen Soren; Pigulski Andrzej; Narwid Artur; Steslicki Marek; Lefever Karolien

来源：Astronomical Journal, 2009, 137(6): 5086-5098.

DOI：10.1088/0004-6256/137/6/5086

• binaries: eclipsing
• binaries: spectroscopic
• open clusters and associations: general
• open clusters and associations: individual (NGC 188)
• stars: evolution
• techniques: photometric
• techniques: spectroscopic

We present time series radial velocity, and photometric observations of a solar-type double-lined eclipsing binary star (V 12) in the old open cluster NGC 188. We use these data to determine the spectroscopic orbit and the photometric elements for V 12. From our analysis, we determine accurate masses (M(p) = 1.103 +/- 0.007 M(circle dot), M(s) = 1.081 +/- 0.007 M(circle dot)) and radii (R(p) = 1.424 +/- 0.019 R(circle dot), R(s) = 1.373 +/- 0.019 R(circle dot)) for the primary (p) and secondary (s) binary components. We adopt a reddening of E(B-V) = 0.087 for NGC 188, and derive component effective temperatures of 5900 +/- 100 K and 5875 +/- 100 K, respectively, for the primary and secondary stars. From their absolute dimensions, the two components of V 12 yield identical distance moduli of V(0) - M(V) = 11(m).24 +/- 0(m).09, corresponding to 1770 +/- 75 pc. Both stars are near the end of their main-sequence evolutionary phase, and are located at the cluster turnoff in the color-magnitude diagram. We determine an age of 6.2 +/- 0.2 Gyr for V 12 and NGC 188, from a comparison with theoretical isochrones in the mass-radius diagram. This age is independent of distance, reddening, and color-temperature transformations. We use isochrones from Victoria-Regina (VRSS) and Yonsei-Yale (Y(2)) with [Fe/H]= -0.1 and [Fe/H] = 0.0. From the solar metallicity isochrones, an age of 6.4 Gyr provides the best fit to the binary components for both sets of models. For the isochrones with [Fe/H]= -0.1, ages of 6.0 Gyr and 5.9 Gyr provide the best fits for the (VRSS) and (Y(2)) models, respectively. We use the distance and age estimates for V 12, together with best estimates for the metallicity and reddening of NGC 188, to investigate the locations of the corresponding VRSS and Y(2) isochrones relative to cluster members in the color-magnitude diagram. Plausible changes in the model metallicity and distance to better match the isochrones to the cluster sequences, result in a range of ages for NGC 188 that is more than 3 times that resulting from our analysis of V 12.

• 出版日期2009-6