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Hubble Space Telescope Snapshot Study of Variable Stars in Globular Clusters: The Inner Region of NGC 6441

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-fo... Full description

Journal Title: The Astronomical Journal 2003, Vol.126(3), pp.1381-1401
Main Author: Pritzl, Barton J.
Other Authors: Smith, Horace A. , Stetson, Peter B. , Catelan, Márcio , Sweigart, Allen V. , Layden, Andrew C. , Rich, R. Michael
Format: Electronic Article Electronic Article
Language: English
Subjects:
ID: ISSN: 0004-6256 ; E-ISSN: 1538-3881 ; DOI: 10.1086/377024
Link: http://dx.doi.org/10.1086/377024
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recordid: iop10.1086/377024
title: Hubble Space Telescope Snapshot Study of Variable Stars in Globular Clusters: The Inner Region of NGC 6441
format: Article
creator:
  • Pritzl, Barton J.
  • Smith, Horace A.
  • Stetson, Peter B.
  • Catelan, Márcio
  • Sweigart, Allen V.
  • Layden, Andrew C.
  • Rich, R. Michael
subjects:
  • Astronomy & Astrophysics
ispartof: The Astronomical Journal, 2003, Vol.126(3), pp.1381-1401
description: 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-overtonemode 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 RR ab and RR c 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 RR c 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 Oosterhoff type I system, its RR Lyrae stars more closely resemble those in Oosterhoff type II globular clusters. However, even compared with typical Oosterhoff type II systems, the mean period of its RR ab 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.
language: eng
source:
identifier: ISSN: 0004-6256 ; E-ISSN: 1538-3881 ; DOI: 10.1086/377024
fulltext: fulltext
issn:
  • 0004-6256
  • 1538-3881
  • 00046256
  • 15383881
url: Link


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titleHubble Space Telescope Snapshot Study of Variable Stars in Globular Clusters: The Inner Region of NGC 6441
creatorPritzl, Barton J. ; Smith, Horace A. ; Stetson, Peter B. ; Catelan, Márcio ; Sweigart, Allen V. ; Layden, Andrew C. ; Rich, R. Michael
ispartofThe Astronomical Journal, 2003, Vol.126(3), pp.1381-1401
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descriptionWe 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-overtonemode 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 RR ab and RR c 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 RR c 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 Oosterhoff type I system, its RR Lyrae stars more closely resemble those in Oosterhoff type II globular clusters. However, even compared with typical Oosterhoff type II systems, the mean period of its RR ab 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.
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0Hubble Space Telescope Snapshot Study of Variable Stars in Globular Clusters: The Inner Region of NGC 6441 Based on observations with the NASA/ESA Hubble Space Telescope , obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.
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descriptionWe 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-overtonemode 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 RR ab and RR c 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 RR c 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 Oosterhoff type I system, its RR Lyrae stars more closely resemble those in Oosterhoff type II globular clusters. However, even compared with typical Oosterhoff type II systems, the mean period of its RR ab 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.
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atitleHubble Space Telescope Snapshot Study of Variable Stars in Globular Clusters: The Inner Region of NGC 6441 Based on observations with the NASA/ESA Hubble Space Telescope , obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.
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abstractWe 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-overtonemode 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 RR ab and RR c 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 RR c 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 Oosterhoff type I system, its RR Lyrae stars more closely resemble those in Oosterhoff type II globular clusters. However, even compared with typical Oosterhoff type II systems, the mean period of its RR ab 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.
doi10.1086/377024
pages1381-1401
date2003-09-01