Bibcode
Kunder, Andrea; Walker, Alistair; Stetson, Peter B.; Bono, Giuseppe; Nemec, James M.; de Propris, Roberto; Monelli, M.; Cassisi, Santi; Andreuzzi, Gloria; Dall'Ora, Massimo; Di Cecco, Alessandra; Zoccali, Manuela
Bibliographical reference
The Astronomical Journal, Volume 141, Issue 1, article id. 15 (2011).
Advertised on:
1
2011
Citations
26
Refereed citations
23
Description
We present period change rates (dP/dt) for 42 RR Lyrae variables in the
globular cluster IC 4499. Despite clear evidence of these period
increases or decreases, the observed period change rates are an order of
magnitude larger than predicted from theoretical models of this cluster.
We find that there is a preference for increasing periods, a phenomenon
observed in most RR Lyrae stars in Milky Way globular clusters. The
period change rates as a function of position in the period-amplitude
plane are used to examine possible evolutionary effects in OoI clusters,
OoII clusters, field RR Lyrae stars, and the mixed-population cluster
ω Centauri. It is found that there is no correlation between the
period change rate and the typical definition of Oosterhoff groups. If
the RR Lyrae period changes correspond with evolutionary effects, this
would be in contrast to the hypothesis that RR Lyrae variables in OoII
systems are evolved horizontal-branch stars that spent their zero-age
horizontal-branch phase on the blue side of the instability strip. This
may suggest that age may not be the primary explanation for the
Oosterhoff types.
Based in part on observations made with the European Southern
Observatory telescopes obtained from the ESO/ST-ECF Science Archive
Facility.