An investigation of the variable stars in the globular cluster NGC 6712.

Abstract

view Abstract Citations (7) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An Investigation of the Variable Stars in the Globular Cluster NGC 6712. Smith, L. L. ; Sandage, A. R. ; Lynden-Bell, D. ; Norton, R. H. Abstract The variable stars in the moderately strong metallic- lined globular cluster NGC 6712 previously studied (Smith and Sandage, Astron. J. 67,121,1962) have been investigated using photographic plates and a photoelectric sequence obtained with the 200-inch telescope between 1955 and 1961. A number of variables were found in a blink survey and we confirm all of Sawyer's previous discoveries. Seven of the variables appear to be RR Lyrae members of the cluster. Periods and light curves in the B and V bandpass were obtained for all seven members, six of which are of Bailey type a or b, and one is of type c. Four variables are of long period and lie at the end of the red-giant branch in the color-magnitude diagram. The purpose of the study was to see if the group characteristics of the variables in NGC 6712 differ from the characteristics in metal-weak clusters such as M3 or in very metal weak clusters such as M 15. Although it appears to be well established that the mean period of type a or b variables in globular clusters correlates well with the metal abundance (longer mean period occurs in the metal- poorer clusters), the six variables in NGC 6712 are not a large enough sample to apply the test because the observed Pa ,~ = 0d54 has little weight. A more stringent test is the differences of the period- amplitude relation between weak- and strong-lined clusters. Defining P1,0 as the period at which the amplitude in blue light is 1.0 mag., we get P3.0 values of 0d66, 0d65, 0d,60, and 0d,57 for M15, M92, M3, and NGC 6712, respectively, placed in the order of increasing metal abundance from the spectroscopic evidence. This decrease of P3.0 may be significant. It agrees with a model designed to explain the difference in mean period Pa,b between clusters (Sandage, 1958 Vatican Symposium on Stellar Populations, p. 51) but accurate data for more clusters are needed before the test can be said to be satisfactory. Publication: The Astronomical Journal Pub Date: September 1963 DOI: 10.1086/109107 Bibcode: 1963AJ.....68R.293S full text sources ADS | data products SIMBAD (2)