The RR Lyrae variables and horizontal branch of NGC 6656 (m22)

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DOIResolve DOI: http://doi.org/10.1088/0004-6256/146/5/119
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TypeArticle
Journal titleAstronomical Journal
ISSN0004-6256
Volume146
Issue5
Article number119
AbstractThe 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〉RR0 = 0.66 ± 0.02 days and 〈P〉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 1/NRR = 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. © 2013. The American Astronomical Society. All rights reserved.
Publication date
LanguageEnglish
AffiliationNational Science Infrastructure; National Research Council Canada
Peer reviewedYes
NPARC number21270371
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Record identifier9cdb938b-a4c8-481a-b319-a93ba00d4853
Record created2014-02-05
Record modified2016-05-09
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