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Title: Tycho- Gaia Astrometric Solution Parallaxes and Proper Motions for Five Galactic Globular Clusters

Abstract

We present a pilot study of Galactic globular cluster (GC) proper motion (PM) determinations using Gaia data. We search for GC stars in the Tycho- Gaia Astrometric Solution (TGAS) catalog from Gaia Data Release 1 (DR1), and identify five members of NGC 104 (47 Tucanae), one member of NGC 5272 (M3), five members of NGC 6121 (M4), seven members of NGC 6397, and two members of NGC 6656 (M22). By taking a weighted average of member stars, fully accounting for the correlations between parameters, we estimate the parallax (and, hence, distance) and PM of the GCs. This provides a homogeneous PM study of multiple GCs based on an astrometric catalog with small and well-controlled systematic errors and yields random PM errors similar to existing measurements. Detailed comparison to the available Hubble Space Telescope ( HST ) measurements generally shows excellent agreement, validating the astrometric quality of both TGAS and HST . By contrast, comparison to ground-based measurements shows that some of those must have systematic errors exceeding the random errors. Our parallax estimates have uncertainties an order of magnitude larger than previous studies, but nevertheless imply distances consistent with previous estimates. By combining our PM measurements with literature positions, distances,more » and radial velocities, we measure Galactocentric space motions for the clusters and find that these also agree well with previous analyses. Our analysis provides a framework for determining more accurate distances and PMs of Galactic GCs using future Gaia data releases. This will provide crucial constraints on the near end of the cosmic distance ladder and provide accurate GC orbital histories.« less

Authors:
;  [1]
  1. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore MD 21218 (United States)
Publication Date:
OSTI Identifier:
22663693
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 839; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCOUNTING; CATALOGS; CORRELATIONS; DISTANCE; ERRORS; GALAXY CLUSTERS; LIMITING VALUES; PROPER MOTION; RADIAL VELOCITY; RANDOMNESS; SIMULATION; SPACE; STARS; TELESCOPES; THERMAL GRAVIMETRIC ANALYSIS

Citation Formats

Watkins, Laura L., and Van der Marel, Roeland P., E-mail: lwatkins@stsci.edu. Tycho- Gaia Astrometric Solution Parallaxes and Proper Motions for Five Galactic Globular Clusters. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA696F.
Watkins, Laura L., & Van der Marel, Roeland P., E-mail: lwatkins@stsci.edu. Tycho- Gaia Astrometric Solution Parallaxes and Proper Motions for Five Galactic Globular Clusters. United States. doi:10.3847/1538-4357/AA696F.
Watkins, Laura L., and Van der Marel, Roeland P., E-mail: lwatkins@stsci.edu. Thu . "Tycho- Gaia Astrometric Solution Parallaxes and Proper Motions for Five Galactic Globular Clusters". United States. doi:10.3847/1538-4357/AA696F.
@article{osti_22663693,
title = {Tycho- Gaia Astrometric Solution Parallaxes and Proper Motions for Five Galactic Globular Clusters},
author = {Watkins, Laura L. and Van der Marel, Roeland P., E-mail: lwatkins@stsci.edu},
abstractNote = {We present a pilot study of Galactic globular cluster (GC) proper motion (PM) determinations using Gaia data. We search for GC stars in the Tycho- Gaia Astrometric Solution (TGAS) catalog from Gaia Data Release 1 (DR1), and identify five members of NGC 104 (47 Tucanae), one member of NGC 5272 (M3), five members of NGC 6121 (M4), seven members of NGC 6397, and two members of NGC 6656 (M22). By taking a weighted average of member stars, fully accounting for the correlations between parameters, we estimate the parallax (and, hence, distance) and PM of the GCs. This provides a homogeneous PM study of multiple GCs based on an astrometric catalog with small and well-controlled systematic errors and yields random PM errors similar to existing measurements. Detailed comparison to the available Hubble Space Telescope ( HST ) measurements generally shows excellent agreement, validating the astrometric quality of both TGAS and HST . By contrast, comparison to ground-based measurements shows that some of those must have systematic errors exceeding the random errors. Our parallax estimates have uncertainties an order of magnitude larger than previous studies, but nevertheless imply distances consistent with previous estimates. By combining our PM measurements with literature positions, distances, and radial velocities, we measure Galactocentric space motions for the clusters and find that these also agree well with previous analyses. Our analysis provides a framework for determining more accurate distances and PMs of Galactic GCs using future Gaia data releases. This will provide crucial constraints on the near end of the cosmic distance ladder and provide accurate GC orbital histories.},
doi = {10.3847/1538-4357/AA696F},
journal = {Astrophysical Journal},
number = 2,
volume = 839,
place = {United States},
year = {Thu Apr 20 00:00:00 EDT 2017},
month = {Thu Apr 20 00:00:00 EDT 2017}
}
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