Deep CCD Photometry in Globular Clusters. IV. M13
Abstract
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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 1986
- DOI:
- 10.1086/164161
- Bibcode:
- 1986ApJ...304..273R
- Keywords:
-
- Charge Coupled Devices;
- Globular Clusters;
- Main Sequence Stars;
- Stellar Spectrophotometry;
- Subdwarf Stars;
- Ubv Spectra;
- Abundance;
- Infrared Spectra;
- Stellar Evolution;
- Stellar Luminosity;
- Astrophysics;
- CLUSTERS: GLOBULAR;
- PHOTOMETRY;
- STARS: ABUNDANCES;
- STARS: EVOLUTION