The Dwarf Spheroidal Companions to M31: Variable Stars in Andromeda VI
The Dwarf Spheroidal Companions to M31: Variable Stars in Andromeda VI
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M31 的矮球体伴星：仙女座 VI 中的变星
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发表时间：
2002
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通讯作者：
G. D. Da Costa
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作者：
B. Pritzl;T. Armandroff;G. Jacoby;G. D. Da Costa
利用哈勃空间望远镜F450 W和F555 W观测资料，对M31的矮球状星系伴星系仙女座VI进行了变星观测。总共发现了118颗变星，包括111颗RR型天琴座恒星，6颗异常造父变星，还有一颗我们无法分类的变星。我们发现，仙女座VI异常造父变星的性质与其他矮球状星系中的异常造父变星一致。我们修改了这些变量的现有的周期光度关系。此外，使用这些和其他可用的数据，我们表明，根本和第一泛音异常造父变星之间没有明显的区别，在较短的周期振幅图，不像RR天琴座星。对于仙女座VI RR型天琴座恒星，我们发现它们在周期-振幅图上靠近奥斯特霍夫I型球状星团，尽管RRab型恒星的平均周期为0.588天，比典型的奥斯特霍夫I型星团稍长。仙女座VI的天琴座RR型星的平均V星等为25.29 ± 0.03，在李、德马克和津恩距离尺度上的距离为815 ± 25 kpc。这与从红巨星分支顶端的I星等导出的距离一致。同样地，天琴座RR型恒星的性质表明仙女座VI的平均丰度与红巨星分支的平均颜色一致。
We have surveyed Andromeda VI, a dwarf spheroidal galaxy companion to M31, for variable stars by using F450W and F555W observations obtained with the Hubble Space Telescope. A total of 118 variables were found, including 111 RR Lyrae stars, six anomalous Cepheids, and one variable that we were unable to classify. We find that the Andromeda VI anomalous Cepheids have properties consistent with those of anomalous Cepheids in other dwarf spheroidal galaxies. We revise the existing period-luminosity relations for these variables. Further, using these and other available data, we show that there is no clear difference between fundamental and first-overtone anomalous Cepheids in a period-amplitude diagram at shorter periods, unlike the RR Lyrae stars. For the Andromeda VI RR Lyrae stars, we find that they lie close to the Oosterhoff type I Galactic globular clusters in the period-amplitude diagram, although the mean period of the RRab stars, ⟨Pab⟩ = 0.588 days, is slightly longer than that of the typical Oosterhoff type I cluster. The mean V magnitude of the RR Lyrae stars in Andromeda VI is 25.29 ± 0.03, resulting in a distance 815 ± 25 kpc on the Lee, Demarque, & Zinn distance scale. This is consistent with the distance derived from the I magnitude of the tip of the red giant branch. Similarly, the properties of the RR Lyrae stars indicate a mean abundance for Andromeda VI that is consistent with that derived from the mean red giant branch color.