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The Distance to NGC 6397 by M-Subdwarf Main-Sequence Fitting

Reid, I. Neill and Gizis, John E. (1998) The Distance to NGC 6397 by M-Subdwarf Main-Sequence Fitting. Astronomical Journal, 116 (6). pp. 2929-2935. ISSN 0004-6256. doi:10.1086/300653.

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Recent years have seen a substantial improvement both in photometry of low-luminosity stars in globular clusters and in modeling the stellar atmospheres of late-type dwarfs. We build on these observational and theoretical advances in undertaking the first determination of the distance to a globular cluster by main-sequence fitting using stars on the lower main sequence. The calibrating stars are extreme M subdwarfs, as classified by Gizis, with parallaxes measured to a precision of better than 10%. Matching against King et al.'s deep [V, (V-I)] photometry of NGC 6397, and adopting E_(B-V) = 0.18 mag, we derive a true distance modulus of 12.13 ± 0.15 mag for the cluster. This compares with (m - M)_0 = 12.24 ± 0.1 derived through conventional main-sequence fitting in the [V, (B-V)] plane. Allowing for intrinsic differences due to chemical composition, we derive a relative distance modulus of δ(m - M)_0 = 2.58 mag between NGC 6397 and the fiducial metal-poor cluster M92. We extend this calibration to other metal-poor clusters and examine the resulting RR Lyrae (MV, [Fe/H]) relation.

Item Type:Article
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URLURL TypeDescription Paper
Gizis, John E.0000-0002-8916-1972
Additional Information:© 1998. The American Astronomical Society. Received 1998 July 7; revised 1998 August 31. We would like to thank Messrs. King, Cool, Piotto, and Anderson for making available the full photometric catalog they have compiled of proper-motion members of NGC 6397. This work was supported partially by NASA grant GO-07385.01-96A from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS 5-26555.
Funding AgencyGrant Number
NASANAS 5-26555
Subject Keywords:Galaxy: halo; globular clusters: individual (NGC 6397)
Issue or Number:6
Record Number:CaltechAUTHORS:20170408-140044774
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Official Citation:I. Neill Reid and John E. Gizis 1998 AJ 116 2929
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:75903
Deposited By: 1Science Import
Deposited On:14 Apr 2017 20:33
Last Modified:15 Nov 2021 16:56

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