Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published December 1998 | Published + Submitted
Journal Article Open

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

Abstract

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.

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.

Attached Files

Published - pdf

Submitted - 9809024.pdf

Files

9809024.pdf
Files (462.2 kB)
Name Size Download all
md5:01bc5c332c16357b09cd373ab1044c6b
173.8 kB Preview Download
pdf
md5:520d2e163e996d3f40cf7681f1afd366
288.4 kB Preview Download

Additional details

Created:
August 22, 2023
Modified:
October 25, 2023