Kurtis A. Williams and Michael Bolte 2007 The Astronomical Journal 133 1490 doi:10.1086/511675
Kurtis A. Williams1,3 and Michael Bolte2
Show affiliationsWe present photometric and spectroscopic studies of the white dwarf (WD) populations in the intermediate-age open clusters NGC 6633 and NGC 7063 as part of the ongoing Lick-Arizona White Dwarf Survey. Using wide-field CCD imaging, we locate 41 candidate WDs in the two cluster fields: 32 in NGC 6633, and 9 in NGC 7063. Spectroscopic observations confirm 13 of these candidates to be bona fide WDs. We describe in detail our Balmer-line fitting technique for deriving effective temperatures and surface gravities from optical DA WD spectra and apply the technique to the 11 DA WDs in the sample. Of these, only two DA WDs are at the cluster distance moduli, one in each cluster. Two more DAs lie 0.75 mag foreground to NGC 6633, raising the possibility that these are double degenerate systems in the cluster. If they are nearly equal-mass binaries, both of these systems likely have combined masses above the Chandrasekhar limit. One DB WD is found to be consistent with membership in NGC 6633, which would make this the third confirmed He-atmosphere WD in an open cluster, although further data are needed to confirm cluster membership. The WD consistent with membership in the cluster NGC 7063 has a low mass (≈0.4 M
), suggesting it may be a He-core WD resulting from close binary evolution. Three of the 11 hydrogen-atmosphere WDs in this study are observed to have Ca II absorption; the number of DAZs in this study is consistent with previous observations that ~25% of field WDs are DAZs.
open clusters and associations: individual (NGC 6633, NGC 7063); white dwarfs
Issue 4 (2007 April)
Received 2006 September 18, accepted for publication 2006 November 29
Published 2007 March 5
Kurtis A. Williams and Michael Bolte 2007 The Astronomical Journal 133 1490
Y. Damerdji et al. 2007 The Astronomical Journal 133 1470
Béla Szilágyi et al 2007 Class. Quantum Grav. 24 S275
Basmah Riaz et al. 2009 ApJ 705 1173
Kim D Anderson 2009 J. Neural Eng. 6 055003
W.-C. Müller and A. Busse 2007 EPL 78 14003
Valeri V. Makarov 2003 The Astronomical Journal 126 1996
J. Maíz Apellániz 2008 ApJ 677 1278
Aldo M. Serenelli et al 2009 ApJ 705 L123
S Klimenko et al 2004 Class. Quantum Grav. 21 S1685