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Title:
WIYN Open Cluster Study. XXXII. Stellar Radial Velocities in the Old Open Cluster NGC 188
Authors:
Geller, Aaron M.; Mathieu, Robert D.; Harris, Hugh C.; McClure, Robert D.
Affiliation:
AA(Department of Astronomy, University of Wisconsin-Madison, WI 53706, USA ; Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under cooperative agreement with the National Science Foundation.), AB(Department of Astronomy, University of Wisconsin-Madison, WI 53706, USA ), AC(United States Naval Observatory, Flagstaff, AZ, 86001, USA ), AD(Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council, 5071 W. Saanich Road, Victoria, BC V9E 2E7, Canada )
Publication:
The Astronomical Journal, Volume 135, Issue 6, pp. 2264-2278 (2008). (AJ Homepage)
Publication Date:
06/2008
Origin:
IOP
AJ Keywords:
binaries: spectroscopic, blue stragglers, open clusters and associations: individual: NGC 188
DOI:
10.1088/0004-6256/135/6/2264
Bibliographic Code:
2008AJ....135.2264G

Abstract

We present the results of our ongoing radial-velocity (RV) survey of the old (7 Gyr) open cluster NGC 188. Our WIYN 3.5 m data set spans a time baseline of 11 years, a magnitude range of 12 <= V <= 16.5 (1.18-0.94 M sun), and a 1° diameter region on the sky. With the addition of a Domain Astrophysical Observatory data set we extend our bright limit to V = 10.8 and, for some stars, extend our time baseline to 35 years. Our magnitude limits include solar-mass main-sequence stars, subgiants, giants, and blue stragglers (BSs), and our spatial coverage extends radially to 17 pc (~13 core radii). For the WIYN data we present a detailed description of our data reduction process and a thorough analysis of our measurement precision of 0.4 km s-1 for narrow-lined stars. We have measured radial velocities for 1046 stars in the direction of NGC 188, and have calculated RV membership probabilities for stars with >=3 measurements, finding 473 to be likely cluster members. We detect 124 velocity-variable cluster members, all of which are likely to be dynamically hard-binary stars. Using our single member stars, we find an average cluster radial velocity of -42.36 ± 0.04 km s-1. We use our precise RV and proper-motion membership data to greatly reduce field-star contamination in our cleaned color-magnitude diagram, from which we identify six stars of note that lie far from a standard single-star isochrone. We present a detailed study of the spatial distribution of cluster-member populations, and find the binaries to be centrally concentrated, providing evidence for the presence of mass segregation in NGC 188. We observe the BSs to populate a bimodal spatial distribution that is not centrally concentrated, suggesting that we may be observing two populations of BSs in NGC 188, including a centrally concentrated distribution as well as a halo population. Finally, we find NGC 188 to have a global RV dispersion of 0.64 ± 0.04 km s-1, which may be inflated by up to 0.23 km s-1 from unresolved binaries. When corrected for unresolved binaries, the NGC 188 RV dispersion has a nearly isothermal radial distribution. We use this mean-corrected velocity dispersion to derive a virial mass of 2300 ± 460 M sun .

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Part 1     Part  3     Part  2     Part  5     Part  6     Part  4     Part  8     Part  7     Part  9     Part 10     Part 11     Part 12     Part 13     Part 14     Part 15     Part 16     Part 17    

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