Exploring Halo Substructure with Giant Stars. I. Survey Description and Calibration of the Photometric Search Technique
Exploring Halo Substructure with Giant Stars. I. Survey Description and Calibration of the Photometric Search Technique
复制标题
DOI：
10.1086/316836
复制
发表时间：
2000-06
期刊：
影响因子：
--
通讯作者：
S. Majewski;J. Ostheimer;W. Kunkel;R. Patterson
中科院分区：
文献类型：
--
作者：
S. Majewski;J. Ostheimer;W. Kunkel;R. Patterson
We have begun a survey of the structure of the Milky Way halo, as well as the halos of other Local Group galaxies, as traced by their constituent giant stars.这些巨星是通过大面积 CCD 光度测量活动来识别的。 Here we present the basis for our photometric search method, which relies on the gravity sensitivity of the Mg I triplet+MgH features near 5150 Å in F–K stars, and which is sensed by the flux in the intermediate-band DDO51 filter. Our technique is a simplified variant of the combined Washington/DDO51 four-filter technique described by Geisler, which we modify for the specific purpose of efficiently identifying distant giant stars for follow-up spectroscopic study: We show here that for most stars the Washington T1-T2 color is correlated monotonically with the Washington M-T2 color with relatively low scatter;出于我们调查的目的，这种相关性消除了在 T1 滤波器中成像的需要，正如 Geisler 最初提出的那样。 To calibrate our (M-T2, M-DDO51) diagram as a means to discriminate field giant stars from nearby dwarfs, we utilize new photometry of the main sequences of the open clusters NGC 3680 and NGC 2477 and the red giant branches of the clusters NGC 3680, Melotte 66, and ω Centauri, supplemented with data on field stars, globular clusters and open clusters by Doug Geisler and合作者。 By combining the data on stars from different clusters, and by taking advantage of the wide abundance spread within ω Centauri, we verify the primary dependence of the M-DDO51 color on luminosity and demonstrate the secondary sensitivity to metallicity among giant stars.我们的实证结果与 Paltoglou 和 Bell 的合成光谱分析结果大体一致。 Finally, we provide conversion formulae from the (M, M-T2) system to the (V, V-I) system, corresponding reddening laws, as well as empirical red giant branch curves from ω Centauri stars for use in deriving photometric parallaxes for giant stars of various metallicities (but equivalent ages) to those of ω Centauri giants.
We have begun a survey of the structure of the Milky Way halo, as well as the halos of other Local Group galaxies, as traced by their constituent giant stars. These giant stars are identified via large-area, CCD photometric campaigns. Here we present the basis for our photometric search method, which relies on the gravity sensitivity of the Mg I triplet+MgH features near 5150 Å in F–K stars, and which is sensed by the flux in the intermediate-band DDO51 filter. Our technique is a simplified variant of the combined Washington/DDO51 four-filter technique described by Geisler, which we modify for the specific purpose of efficiently identifying distant giant stars for follow-up spectroscopic study: We show here that for most stars the Washington T1-T2 color is correlated monotonically with the Washington M-T2 color with relatively low scatter; for the purposes of our survey, this correlation obviates the need to image in the T1 filter, as originally proposed by Geisler. To calibrate our (M-T2, M-DDO51) diagram as a means to discriminate field giant stars from nearby dwarfs, we utilize new photometry of the main sequences of the open clusters NGC 3680 and NGC 2477 and the red giant branches of the clusters NGC 3680, Melotte 66, and ω Centauri, supplemented with data on field stars, globular clusters and open clusters by Doug Geisler and collaborators. By combining the data on stars from different clusters, and by taking advantage of the wide abundance spread within ω Centauri, we verify the primary dependence of the M-DDO51 color on luminosity and demonstrate the secondary sensitivity to metallicity among giant stars. Our empirical results are found to be generally consistent with those from analysis of synthetic spectra by Paltoglou & Bell. Finally, we provide conversion formulae from the (M, M-T2) system to the (V, V-I) system, corresponding reddening laws, as well as empirical red giant branch curves from ω Centauri stars for use in deriving photometric parallaxes for giant stars of various metallicities (but equivalent ages) to those of ω Centauri giants.