PERIOD CHANGE SIMILARITIES AMONG THE RR LYRAE VARIABLES IN OOSTERHOFF I AND OOSTERHOFF II GLOBULAR SYSTEMS
- NOAO-Cerro Tololo Inter-American Observatory, Casilla 603, La Serena (Chile)
- Herzberg Institute of Astrophysics, National Research Council, Victoria, BC V9E 2E7 (Canada)
- Dipartimento di Fisica, Universita' di Roma Tor Vergata, via della Ricerca Scientifica 1, I-00133 Roma (Italy)
- Department of Physics and Astronomy, Camosun College, Victoria, BC (Canada)
- IAC, Calle Via Lactea, E-38200 La Laguna, Tenerife (Spain)
- INAF-Osservatorio Astronomico di Collurania, via M. Maggini, I-64100 Teramo (Italy)
- Fundacion Galileo Galilei-INAF, Brena Baja, Tenerife (Spain)
- INAF-Osservatorio Astronomico di Capodimonte, via Moiarello 16, I-80131 Napoli (Italy)
- Departamento de Astronomia y Astrofisica, P. Universidad Catolica, Casilla 306, Santiago 22 (Chile)
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 {omega} 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.
- OSTI ID:
- 21583274
- Journal Information:
- Astronomical Journal (New York, N.Y. Online), Journal Name: Astronomical Journal (New York, N.Y. Online) Journal Issue: 1 Vol. 141; ISSN 1538-3881
- Country of Publication:
- United States
- Language:
- English
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