狮子座IV矮球状星系：色星等图和脉动星
The Leo IV dwarf spheroidal galaxy: color-magnitude diagram and pulsating stars
摘要：
我们提出的第一个V，B-V色星等图狮子座IV矮球状星系，一个暗淡的银河系卫星最近发现的斯隆数字巡天。我们已经获得了B，V时间序列测光达到约半个星等以下的狮子座IV关闭，我们在V= 24.7等检测，并进行了第一次研究的变星人口。我们已经确定了银河系中的三颗RR型天琴座恒星（都是基模变星，RRab）和一颗SX型凤凰座变星。在周期-振幅图中，狮子座IV型RR天琴座星位于靠近奥斯特霍夫I型系统和银河系球状星团M3中演化的基模RR天琴座星的位置。然而，它们的平均脉动周期，$<P{\rm ab}>$ =0.655天，表明该星系属于奥斯特霍夫II型。天琴座RR型恒星很好地跟踪了星系的水平分支，将其平均星等设置为$<V_{\rm RR}>= 21.48 \pm 0.03$等（平均值的标准差）。通过对Leo IV dSph采用变红的$E(B-V) = 0.04 \pm 0.01$ mag和[Fe/H] = -2.31 $\pm$ 0.10的金属丰度，这导致$μ_{0}=20.94 \pm 0.07$ mag的距离模量，对应于$154 \pm 5$ kpc的距离。
英文摘要：
We present the first V, B-V color-magnitude diagram of the Leo IV dwarf spheroidal galaxy, a faint Milky Way satellite recently discovered by the Sloan Digital Sky Survey. We have obtained B,V time-series photometry reaching about half a magnitude below the Leo IV turnoff, which we detect at V= 24.7 mag, and have performed the first study of the variable star population. We have identified three RR Lyrae stars (all fundamental-mode pulsators, RRab) and one SX Phoenicis variable in the galaxy. In the period-amplitude diagram the Leo IV RR Lyrae stars are located close to the loci of Oosterhoff type I systems and the evolved fundamental-mode RR Lyrae stars in the Galactic globular cluster M3. However, their mean pulsation period, $<P{\rm ab}>$=0.655 days, would suggest an Oosterhoff type II classification for this galaxy. The RR Lyrae stars trace very well the galaxy's horizontal branch, setting its average magnitude at $<V_{\rm RR}>= 21.48 \pm 0.03$ mag (standard deviation of the mean). This leads to a distance modulus of $μ_{0}=20.94 \pm 0.07$ mag, corresponding to a distance of $154 \pm 5$ kpc, by adopting for the Leo IV dSph a reddening $E(B-V) = 0.04 \pm 0.01$ mag and a metallicity of [Fe/H] = -2.31 $\pm$ 0.10.
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