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Title: THE RR LYRAE VARIABLES AND HORIZONTAL BRANCH OF NGC 6656 (M22) {sup ,}

The first calibrated broadband UBVI time-series photometry is presented for the RR Lyrae variable stars in NGC 6656 (M22), with observations spanning a range of 22 years. We have also redetermined the variability types and periods for the RR Lyrae stars identified previously by photographic observations, revising the number of fundamental-mode RR Lyrae variables (RR0) to 10 and the number of first-overtone variables (RR1) to 16. The mean periods of the RR0 and RR1 variables are (P) {sub RR0} = 0.66 ± 0.02 days and (P) {sub RR1} = 0.33 ± 0.01 days, respectively, supporting an Oosterhoff II classification for the cluster. The number ratio of RR1-type to all RR-type variables is N {sub 1}/N{sub RR} = 0.61, also consistent with an Oosterhoff II designation. Both the RR Lyrae stars' minimum light colors and the blue edge of the RR Lyrae instability strip suggest E( B – – V) = 0.36 ± 0.02 mag toward M22. Regarding the HB morphology of M22, we find (B-R)/(B+V+R) = +0.97 ± 0.1 and at least one ''gap'' located in an unusual part of the blue HB, in the middle of the so-called hot HB stars.
Authors:
; ;  [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [7] ;  [8] ;  [9] ;  [10] ;  [11]
  1. Cerro Tololo Inter-American Observatory, Casilla 603, La Serena (Chile)
  2. Dominion Astrophysical Observatory, NRC-Herzberg, National Research Council, Victoria BC, V9E 2E7 (Canada)
  3. INAF-Osservatorio Astronomico di Collurania, Via M. Maggini, I-64100 Teramo (Italy)
  4. Bowling Green State University, Bowling Green, OH 43403 (United States)
  5. Dipartimento di Fisica, Universita di Roma Tor Vergata, Rome (Italy)
  6. Pontificia Universidad Católica de Chile, Departamento de Astronomía y Astrofísica, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago (Chile)
  7. Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803-4001 (United States)
  8. Department of Astronomy, School of Science, The University of Tokyo (Japan)
  9. Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD (United Kingdom)
  10. Korea Astronomy and Space Science Institute, Daejeon 305-348 (Korea, Republic of)
  11. Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755 (United States)
Publication Date:
OSTI Identifier:
22273321
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (New York, N.Y. Online); Journal Volume: 146; Journal Issue: 5; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTRONOMY; ASTROPHYSICS; COLOR; DISTANCE; GALAXIES; MORPHOLOGY; PHOTOGRAPHY; PHOTOMETRY; STAR EVOLUTION; VARIABLE STARS; VISIBLE RADIATION