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The Absolute Proper Motion of Palomar 12: A Case for Tidal Capture from the Sagittarius Dwarf Spheroidal Galaxy
Dana I. Dinescu,Steven R. Majewski,Terrence M. Girard, andKyle M. Cudworth
© 2000. The American Astronomical Society. All rights reserved. Printed in U.S.A.
The Astronomical Journal,Volume 120,Number 4Citation Dana I. Dinescuet al 2000AJ120 1892DOI 10.1086/301552
Dana I. Dinescu
AFFILIATIONS
Department of Astronomy, University of Virginia, Charlottesville, VA 22903-0818
Steven R. Majewski
AFFILIATIONS
Department of Astronomy, University of Virginia, Charlottesville, VA 22903-0818
Visiting Associate, Observatories of the Carnegie Institution of Washington; David and Lucile Packard Foundation Fellow; Cottrell Scholar
Terrence M. Girard
AFFILIATIONS
Astronomy Department, Yale University, P.O. Box 208101, New Haven, CT 06520-8101
Kyle M. Cudworth
AFFILIATIONS
Yerkes Observatory, P.O. Box 258, Williams Bay, WI 53191-0258
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- Received2000 March 13
- Accepted2000 June 21
Abstract
We have measured the absolute proper motion of the young globular cluster Pal 12 with respect to background galaxies, using plate material spanning a 40 yr time baseline, and measuring stars down to a magnitudeV ∼ 22. The measured absolute proper motion has an uncertainty of 0.3 mas yr-1 in each coordinate. Pal 12's young age for a globular cluster led to the hypothesis that the cluster originated in the Large Magellanic Cloud (LMC) and was later captured by the Milky Way (Lin & Richer). Here we investigate this hypothesis using the complete kinematical data. We present the orbital characteristics of Pal 12 and compare them with those of the LMC and Sagittarius dwarf galaxy (Sgr). The present kinematical data suggest that, from the two parent candidates for Pal 12, Sgr presents a more plausible case for the host galaxy than the LMC. We explore this scenario in the context of the uncertainties in the orbits and using two different analyses: the direct comparison of the orbits of Pal 12 and Sgr as a function of time, and the analytical model of Sgr's tidal disruption developed by Johnston. We find that, within the present uncertainties of the observables, this scenario is viable in both methods. Moreover, both methods place this event at the same point in time. Our best estimate of the time of Pal 12's tidal capture from Sgr is ∼1.7 Gyr ago.
