Hubble Space Telescope snapshot study of variable stars in globular clusters:: The inner region of NGC 6441

被引:81
作者
Pritzl, BJ
Smith, HA
Stetson, PB
Catelan, M
Sweigart, AV
Layden, AC
Rich, RM
机构
[1] Michigan State Univ, Dept Phys & Astron, E Lansing, MI 48824 USA
[2] Natl Res Council Canada, Herzberg Inst Astrophys, Dominion Astrophys Observ, Victoria, BC V9E 2E7, Canada
[3] Pontificia Univ Catolica Chile, Dept Astron & Astrofis, Santiago, Chile
[4] NASA, Astron & Solar Phys Lab, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA
[5] Bowling Green State Univ, Dept Phys & Astron, Bowling Green, OH 43403 USA
[6] Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90095 USA
关键词
globular clusters : individual (NGC 6441); RR Lyrae variable;
D O I
10.1086/377024
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We present the results of a Hubble Space Telescope snapshot program to survey the inner region of the metal-rich globular cluster NGC 6441 for its variable stars. A total of 57 variable stars were found, including 38 RR Lyrae stars, six Population II Cepheids, and 12 long-period variables. Twenty-four of the RR Lyrae stars and all of the Population II Cepheids were previously undiscovered in ground-based surveys. Of the RR Lyrae stars observed in this survey, 26 are pulsating in the fundamental mode with a mean period of 0.753 days and 12 are first-overtone-mode pulsators with a mean period of 0.365 days. These values match up very well with those found in ground- based surveys. Combining all the available data for NGC 6441, we find mean periods of 0.759 and 0.375 days for the RRab and RRc stars, respectively. We also find that the RR Lyrae stars in this survey are located in the same regions of a period-amplitude diagram as those found in ground- based surveys. The overall ratio of RRc to total RR Lyrae stars is 0.33. Although NGC 6441 is a metal-rich globular cluster and would, on that ground, be expected either to have few RR Lyrae stars or to be an Oosterho. type I system, its RR Lyrae stars more closely resemble those in Oosterho. type II globular clusters. However, even compared with typical Oosterho. type II systems, the mean period of its RRab stars is unusually long. We also derived I-band period-luminosity relations for the RR Lyrae stars. Of the six Population II Cepheids, five are of W Virginis type and one is a BL Herculis variable star. This makes NGC 6441, along with NGC 6388, the most metal-rich globular cluster known to contain these types of variable stars. Another variable, V118, may also be a Population II Cepheid, given its long period and its separation in magnitude from the RR Lyrae stars. We examine the period-luminosity relation for these Population II Cepheids and compare it with those in other globular clusters and in the Large Magellanic Cloud. We argue that there does not appear to be a change in the period-luminosity relation slope between the BL Herculis and W Virginis stars, but that a change of slope does occur when the RV Tauri stars are added to the period-luminosity relation.
引用
收藏
页码:1381 / 1401
页数:21
相关论文
共 93 条
[1]   Image subtraction using a space-varying kernel [J].
Alard, C .
ASTRONOMY & ASTROPHYSICS SUPPLEMENT SERIES, 2000, 144 (02) :363-370
[2]   The MACHO project LMC variable star inventory. VII. The discovery of RV Tauri stars and new type II Cepheids in the large magellanic cloud [J].
Alcock, C ;
Allsman, RA ;
Alves, DR ;
Axelrod, TS ;
Becker, A ;
Bennett, DP ;
Cook, KH ;
Freeman, KC ;
Griest, K ;
Lawson, WA ;
Lehner, MJ ;
Marshall, SL ;
Minniti, D ;
Peterson, BA ;
Pollard, KR ;
Pratt, MR ;
Quinn, PJ ;
Rodgers, AW ;
Sutherland, W ;
Tomaney, A ;
Welch, DL .
ASTRONOMICAL JOURNAL, 1998, 115 (05) :1921-1933
[3]   COLOR-MAGNITUDE DIAGRAMS FOR 7 GLOBULAR CLUSTERS [J].
ARP, HC .
ASTRONOMICAL JOURNAL, 1955, 60 (09) :317-337
[4]   CEPHEIDS OF PERIOD GREATER THAN ONE DAY IN GLOBULAR CLUSTERS [J].
ARP, HC .
ASTRONOMICAL JOURNAL, 1955, 60 (01) :1-17
[5]   SEARCH FOR VARIABLES IN GLOBULAR CLUSTER NGC 7492 [J].
BARNES, SA .
ASTRONOMICAL JOURNAL, 1968, 73 (07) :579-&
[6]   Astrometry with the Hubble Space Telescope:: A parallax of the fundamental distance calibrator RR Lyrae [J].
Benedict, GF ;
McArthur, BE ;
Fredrick, LW ;
Harrison, TE ;
Lee, J ;
Slesnick, CL ;
Rhee, J ;
Patterson, RJ ;
Nelan, E ;
Jefferys, WH ;
van Altena, W ;
Shelus, PJ ;
Franz, OG ;
Wasserman, LH ;
Hemenway, PD ;
Duncombe, RL ;
Story, D ;
Whipple, AL ;
Bradley, AJ .
ASTRONOMICAL JOURNAL, 2002, 123 (01) :473-484
[7]   RR LYRAE VARIABLES IN A GALACTIC BULGE WINDOW [J].
BLANCO, BM .
ASTRONOMICAL JOURNAL, 1992, 103 (06) :1872-1927
[8]  
Bono G, 1997, ASTRON ASTROPHYS, V317, P171
[9]   Nonlinear investigation of the pulsational properties of RR Lyrae variables [J].
Bono, G ;
Caputo, F ;
Castellani, V ;
Marconi, M .
ASTRONOMY & ASTROPHYSICS SUPPLEMENT SERIES, 1997, 121 (02) :327-341
[10]   Theoretical insights into the RR lyrae K-band period-luminosity relation [J].
Bono, G ;
Caputo, F ;
Castellani, V ;
Marconi, M ;
Storm, J .
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 2001, 326 (03) :1183-1190