Deep CCD photometry in globular clusters. IV - M13

Details Deep CCD photometry in globular clusters. IV - M13 Deep CCD photometry in globular clusters. IV - M13

May 1986

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986apj...304..273r&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 304, May 1, 1986, p. 273-282. NSERC-supported research.

Astronomy and Astrophysics

Astrophysics

81

Charge Coupled Devices, Globular Clusters, Main Sequence Stars, Stellar Spectrophotometry, Subdwarf Stars, Ubv Spectra, Abundance, Infrared Spectra, Stellar Evolution, Stellar Luminosity

Scientific paper

CCD photometry in U, B, and V is presented for a single field measuring 2.0 x 3.5 arcmin in the globular cluster M13. The photometry reaches fainter than V = 25. The intrinsic main-sequence width of M13 does not exceed 0.015 mag in B-V, and this restricts any metallicity variation among its main-sequence stars to less than 30 percent. The main-sequence binary frequency in the field studied does not exceed 1.4 percent. Using a new calibration of the ultraviolet excess of main-sequence stars in terms of metallicity derived from infrared observations, it is estimated that the Fe/H abundance ratio is -1.4 for M13. The distance to M13 was determined by fitting a main sequence defined by subdwarfs to the M13 main-sequence fiducial. This results in (m-M)(v) = 14.50 + or - 0.26 if the Lutz-Kelker (1973) statistical corrections are applied to the subdwarfs and 14.39 if they are not used. An age of 16 + or - 2 Gyr is derived for M13 from an overlay of a set of isochrones developed by VandenBerg and Bell (1985). Finally, the main-sequence luminosity function is found to be still steeply rising at the limit of the photometry, M(v) = 10.5.

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