M4 the closest globular cluster.
Abstract
A BV photometric investigation of the bright southern globular cluster M4 was carried out using the 1-m telescope of Cerro Las Campanas (CARSO). Seventeen stars were observed photoelectrically; the limiting magnitude was 15.80. Using this sequence, 531 stars were measured photographically. The apparent distance modulus from the mean visual magnitude of 30 horizontal-branch RR Lyrae stars within a radius of 9.3 min from the cluster center and with a value of plus 0.6 adopted for their absolute magnitude is 12.86. The estimated distance is 1.75 kpc, making it the closest globular cluster to the sun. This cluster is highly reddened by a BV magnitude of 0.55 because of the dark nebulosity in Scorpio-Ophiuchus. The giant branch rises 2.45 magnitudes above the horizontal branch at a BV magnitude of 1.4, characteristic of an object of medium metallicity.
- Publication:
-
Astronomy and Astrophysics Supplement Series
- Pub Date:
- July 1975
- Bibcode:
- 1975A&AS...21....5A
- Keywords:
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- Astronomical Photometry;
- Globular Clusters;
- Ubv Spectra;
- Astronomical Photography;
- Cepheid Variables;
- Electrophotometers;
- Giant Stars;
- Stellar Luminosity;
- Stellar Spectrophotometry;
- Tables (Data);
- Astronomy