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Title: Proper motion with HST: Searching for high-velocity stars in the core of the globular cluster 47 Tucanae

Abstract

Binary stars play an essential role during the late phases of the dynamical evolution of a globular cluster. They transfer energy to passing stars and so can strongly influence the cluster evolution, enough to delay, halt, and even reverse core collapse. Hard binaries are known to exist in cluster cores, e.g., in the form of millisecond pulsars (about half of the millisecond pulsars observed in 47 Tucanae are such hard binaries). The presence of hard binaries may also be revealed by searching for the by-products of close encounters: high- velocity stars, such as those discovered in the core of 47 Tuc by Meylan et al. (1991) and Gebhardt et al. (1995). These studies represent the limit of the radial velocity data which can be obtained from the ground. If more progress is to be made, it must come through obtaining proper motions--a task for which {ital only} the Hubble Space Telescope (HST) is suitable. We are using WFPC2 to obtain deep U (F300W) images of the core of 47 Tuc at three different epochs over two years, with which we will measure differential proper motions to a 1-{sigma} limit of 0.23 mas/yr. This--rather conservative--estimate corresponds to a 5-{sigma} detection ofmore » all stars with tangential velocities greater than 22 km s{sup -1}. By using the F300W filter we can measure stars over the whole color-magnitude diagram, from the red-giant branch to well down the main sequence. Such a complete census will provide unique constraints as a function of the stellar mass on relaxation processes, collision and ejection rates, and the velocity distribution. Here we report on the first-epoch (Cycle 5) observations of this project. Although no proper motions are available yet, some preliminary by-product results are presented. These include luminosity functions and color-magnitude diagrams for the core of 47 Tuc and the light curves of variable blue straggler stars and of a candidate X-ray source. 32 refs., 5 figs.« less

Authors:
 [1];  [2];  [3];  [4];  [5];  [6]
  1. European Southern Observatory, Garching b. Muenchen, (Germany)
  2. Lawrence Livermore National Lab., CA (United States)
  3. Rutgers, Univ., Dept. of Physics and Astronomy, New Jersey (United States)
  4. Anglo-Australian Observatory, Epping, NSW (Australia)
  5. Theoretical Astrophysics, Caltech, Pasadena, (United States)
  6. Eagle-Picher Industries, Inc., Joplin, MO (United States). Electronics Div.
Publication Date:
Research Org.:
Lawrence Livermore National Lab., CA (United States)
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
211576
Report Number(s):
UCRL-JC-123358; CONF-951225-1
ON: DE96008378
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Technical Report
Resource Relation:
Conference: Conference: science with the Hubble Space Telescope II, Paris (France), 4-8 Dec 1995; Other Information: PBD: 13 Feb 1996
Country of Publication:
United States
Language:
English
Subject:
66 PHYSICS; STAR CLUSTERS; BINARY STARS; DYNAMICS; PROPER MOTION; NUMERICAL DATA; TELESCOPES

Citation Formats

Meylan, G, Minniti, D, Pryor, C, Tinney, C G, Phinney, E S, and Sams, B. Proper motion with HST: Searching for high-velocity stars in the core of the globular cluster 47 Tucanae. United States: N. p., 1996. Web. doi:10.2172/211576.
Meylan, G, Minniti, D, Pryor, C, Tinney, C G, Phinney, E S, & Sams, B. Proper motion with HST: Searching for high-velocity stars in the core of the globular cluster 47 Tucanae. United States. https://doi.org/10.2172/211576
Meylan, G, Minniti, D, Pryor, C, Tinney, C G, Phinney, E S, and Sams, B. Tue . "Proper motion with HST: Searching for high-velocity stars in the core of the globular cluster 47 Tucanae". United States. https://doi.org/10.2172/211576. https://www.osti.gov/servlets/purl/211576.
@article{osti_211576,
title = {Proper motion with HST: Searching for high-velocity stars in the core of the globular cluster 47 Tucanae},
author = {Meylan, G and Minniti, D and Pryor, C and Tinney, C G and Phinney, E S and Sams, B},
abstractNote = {Binary stars play an essential role during the late phases of the dynamical evolution of a globular cluster. They transfer energy to passing stars and so can strongly influence the cluster evolution, enough to delay, halt, and even reverse core collapse. Hard binaries are known to exist in cluster cores, e.g., in the form of millisecond pulsars (about half of the millisecond pulsars observed in 47 Tucanae are such hard binaries). The presence of hard binaries may also be revealed by searching for the by-products of close encounters: high- velocity stars, such as those discovered in the core of 47 Tuc by Meylan et al. (1991) and Gebhardt et al. (1995). These studies represent the limit of the radial velocity data which can be obtained from the ground. If more progress is to be made, it must come through obtaining proper motions--a task for which {ital only} the Hubble Space Telescope (HST) is suitable. We are using WFPC2 to obtain deep U (F300W) images of the core of 47 Tuc at three different epochs over two years, with which we will measure differential proper motions to a 1-{sigma} limit of 0.23 mas/yr. This--rather conservative--estimate corresponds to a 5-{sigma} detection of all stars with tangential velocities greater than 22 km s{sup -1}. By using the F300W filter we can measure stars over the whole color-magnitude diagram, from the red-giant branch to well down the main sequence. Such a complete census will provide unique constraints as a function of the stellar mass on relaxation processes, collision and ejection rates, and the velocity distribution. Here we report on the first-epoch (Cycle 5) observations of this project. Although no proper motions are available yet, some preliminary by-product results are presented. These include luminosity functions and color-magnitude diagrams for the core of 47 Tuc and the light curves of variable blue straggler stars and of a candidate X-ray source. 32 refs., 5 figs.},
doi = {10.2172/211576},
url = {https://www.osti.gov/biblio/211576}, journal = {},
number = ,
volume = ,
place = {United States},
year = {1996},
month = {2}
}