A Photometric and Spectroscopic Search for White Dwarfs in the Open Clusters NGC 6633 and NGC 7063
A Photometric and Spectroscopic Search for White Dwarfs in the Open Clusters NGC 6633 and NGC 7063
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疏散星团 NGC 6633 和 NGC 7063 中白矮星的光度和光谱搜索
DOI：
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发表时间：
2006
期刊：
影响因子：
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通讯作者：
M. Bolte
中科院分区：
文献类型：
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作者：
K. Williams;M. Bolte
我们目前的光度和光谱研究的白色矮星（WD）人口的中间年龄疏散星团NGC 6633和NGC 7063的一部分，正在进行的利克亚利桑那州白色矮星调查。使用宽视场CCD成像，我们在两个星团区域中定位了41个候选WD：NGC 6633中的32个和NGC 7063中的9个。光谱观测证实其中13个候选者是真正的WD。我们详细描述了我们的Balmer线拟合技术推导出有效的温度和表面重力从光学DA WD光谱，并将该技术应用于样品中的11 DA WD。其中，只有两个DA WD处于聚类距离模数，每个聚类中有一个。另外两个0.75等的DA位于NGC 6633的前景，增加了它们是星团中双简并系统的可能性。如果它们是几乎相等质量的双星，那么这两个系统的总质量可能都超过了克拉塞卡极限。一个DB WD被发现与NGC 6633的成员一致，这将使其成为疏散星团中第三个被证实的He大气WD，尽管需要进一步的数据来确认星团成员。与星系团NGC 7063的成员一致的WD具有低质量（约0.4 M <$），表明它可能是由近距离双星演化产生的He核WD。在这项研究中的11个氢-大气WD中有三个被观察到具有Ca II吸收;这项研究中DAZ的数量与之前的观察结果一致，即大约25%的现场WD是DAZ。
We 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.