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

Journal Article · Mon Jun 15 00:00:00 EDT 2009 · Astronomical Journal (New York, N.Y. Online)

DOI:https://doi.org/10.1088/0004-6256/137/6/5086; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)· OSTI ID:21255712

Meibom, Soeren; Mathieu, Robert D ^[1]; Grundahl, Frank; Frandsen, Soeren ^[2]; Clausen, Jens Viggo ^[3]; Pigulski, Andrzej; Narwid, Artur; Steslicki, Marek ^[4]; Lefever, Karolien ^[5]

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1. University of Wisconsin-Madison, WI (United States)
2. Department of Physics and Astronomy, Aarhus University (Denmark)
3. Niels Bohr Institute, Copenhagen University (Denmark)
4. Instytut Astronomiczny Uniwersytetu Wroclawskiego, Kopernika 11, 51-622 Wroclaw (Poland)
5. Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, 3001 Heverlee (Belgium)

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{sub p} = 1.103 {+-} 0.007 M {sub sun}, M{sub s} = 1.081 {+-} 0.007 M {sub sun}) and radii (R{sub p} = 1.424 {+-} 0.019 R {sub sun}, R{sub s} = 1.373 {+-} 0.019 R {sub sun}) for the primary (p) and secondary (s) binary components. We adopt a reddening of E {sub 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 {sub 0} - M{sub V} = 11fm24 {+-} 0fm09, 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 {sup 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 {sup 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 {sup 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.

• OSTI ID: 21255712
• Journal Information: Astronomical Journal (New York, N.Y. Online), Vol. 137, Issue 6; Other Information: DOI: 10.1088/0004-6256/137/6/5086; Country of input: International Atomic Energy Agency (IAEA); ISSN 1538-3881
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE
BINARY STARS
COLOR
DIAGRAMS
MASS
ORBITS
RADIAL VELOCITY
STAR EVOLUTION
TRANSFORMATIONS