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Hubble Space Telescope observations of the Draco dwarf spheroidal galaxy

Grillmair, Carl J. and Mould, Jeremy R. and Holtzman, Jon A. and Worthey, Guy and Ballester, Gilda E. and Burrows, Christopher J. and Clarke, John T. and Crisp, David and Evans, Robin W. and Gallagher, John S., III and Griffiths, Richard E. and Hester, J. Jeff and Hoessel, John G. and Scowen, Paul A. and Stapelfeldt, Karl R. and Trauger, John T. and Watson, Alan M. and Westphal, James A. (1998) Hubble Space Telescope observations of the Draco dwarf spheroidal galaxy. Astronomical Journal, 115 (1). pp. 144-151. ISSN 0004-6256. doi:10.1086/300169.

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We present an F606W-F814W color-magnitude diagram for the Draco dwarf spheroidal galaxy based on Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) images. The luminosity function is well sampled to ~3 mag below the turnoff. We see no evidence for multiple turnoffs and conclude that, at least over the field of view of the WFPC2, star formation was primarily single-epoch. If the observed number of blue stragglers is due to extended star formation, then roughly 6% (upper limit) of the stars could be half as old as the bulk of the galaxy. The color difference between the red giant branch and the turnoff is consistent with an old population and is very similar to that observed in the old, metal-poor Galactic globular clusters M68 and M92. Despite its red horizontal branch, Draco appears to be older than M68 and M92 by 1.6 ± 2.5 Gyr, lending support to the argument that the "second parameter" that governs horizontal-branch morphology must be something other than age. Draco's observed luminosity function is very similar to that of M68, and the derived initial mass function is consistent with that of the solar neighborhood.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Grillmair, Carl J.0000-0003-4072-169X
Mould, Jeremy R.0000-0003-3820-1740
Crisp, David0000-0002-4573-9998
Gallagher, John S., III0000-0001-8608-0408
Stapelfeldt, Karl R.0000-0002-2805-7338
Alternate Title:Hubble Space Telescope Observations of the Draco Dwarf Spheroidal
Additional Information:© 1998 American Astronomical Society. Received 1997 June 18; revised 1997 September 24. We are grateful to Gary da Costa for a critical reading of an earlier version of this manuscript. This research was conducted by the WFPC2 Investigation Definition Team, supported in part by NASA grant NAS 7-1260.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
NASANAS 7-1260
NASANAS 5-26555
Subject Keywords:galaxies: abundances; galaxies: elliptical and lenticular, cD; galaxies: evolution; galaxies: individual (Draco); Local Group
Issue or Number:1
Record Number:CaltechAUTHORS:20150121-152955114
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Official Citation:Hubble Space Telescope Observations of the Draco Dwarf Spheroidal Galaxy Carl J. Grillmair et al. 1998 The Astronomical Journal 115 144
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:53966
Deposited By: Ruth Sustaita
Deposited On:22 Jan 2015 00:08
Last Modified:10 Nov 2021 20:25

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