Stellar Populations in the Dwarf Elliptical Galaxy NGC 147
Stellar Populations in the Dwarf Elliptical Galaxy NGC 147
复制标题
矮椭圆星系 NGC 147 中的恒星群
DOI：
--
复制
发表时间：
1993
期刊：
影响因子：
--
通讯作者：
B. Madore
中科院分区：
文献类型：
--
作者：
M. Lee;W. Freedman;B. Madore
用哈勃空间望远镜上的广角行星照相机2（WFPC 2）获得了本星系群矮椭圆星系NGC 147的中心和外围的深V和深I CCD图像。颜色星等图显示了许多有趣的特征，包括一个定义明确的红巨星分支（RGB），一个红色水平分支（HB），一个强烈的红色团块，以及少量的
扩展渐近巨星分支（EAGB）星。基于HB和RGB尖端亮度两者导出平均距离模数（m-M）_0=24.39。由RGB颜色确定的金属丰度[Fe/H]在中心场的平均值为-0.91，在外场的平均值为-1.0;外场显示出金属丰度随银河系中心半径增加的微弱趋势。银河系中也存在金属丰度色散，它显示出明显的径向变化，在这个意义上，在较小的半径处可以看到较大的色散。EAGB星的小种群表明存在中等年龄（几个Gyr）的恒星，
而M v< 1的主序星的缺失表明星星的形成至少在1 Gyr前停止。EAGB恒星的分布表明，年轻恒星比大多数老恒星更集中。HB星的相对分布也暗示了类似的年龄梯度，这些恒星在较大半径处似乎人口更多。这些结果被认为是矮椭圆星系演化的理论模型的背景下。
Deep V and I CCD images in a central and an outer field of the Local Group dwarf elliptical galaxy NGC 147 have been obtained with the Wide Field and Planetary Camera-2 (WFPC2) on board of the Hubble Space Telescope. The color-magnitude diagram shows a number of interesting features, including a well defined red giant branch (RGB), a red horizontal branch (HB), a strong red clump, and a small number of
extended asymptotic giant branch (EAGB) stars. A mean distance modulus of (m- M)_0=24.39 is derived based on both the HB and the RGB tip brightness. The metallicity [Fe/H] as determined from the RGB color has a mean value of -0.91 in the central field, and -1.0 in the outer field; and the outer field shows a weak tendency of increasing metallicity with galactocentric radius. A metallicity dispersion is also present in the galaxy, and it shows a clear radial variation in the sense that a larger dispersion is seen at smaller radii. The small population of EAGB stars indicates the presence of intermediate-aged (several Gyr) stars in the
galaxy, while the absence of the main sequence stars with M v< 1 shows that star formation ceased at least 1 Gyr ago. The distribution of the EAGB stars indicates that the younger stars are more centrally concentrated than the majority of older stars. A similar age gradient is also implied by the relative distribution of the HB stars, which appear to be more populous at larger radii. These results are considered within the context of theoretical models for the evolution of dwarf elliptical galaxies.