标题： 哈勃空间望远镜观测M32：色- magnitude 图表 显示英文标题

标题： Hubble Space Telescope Observations of M32: The Color-Magnitude Diagram

摘要： 我们基于哈勃空间望远镜WFPC2图像，给出了M32中心1′-2′区域内的V-I色星等图。红巨星宽广的颜色-光度分布表明恒星群体由具有广泛金属丰度的恒星组成。这种分布无法用年龄的变化来解释。巨星分支的蓝色一侧延伸到M_I约-4.0，并可用[Fe/H]约为-1.5的等年龄曲线拟合。红色一侧由一个密集且占主导地位的序列构成，该序列在M_I约-3.2处达到顶点，并延伸至V-I=4以上。该序列可用-0.2<[Fe/H]<+0.1的等年龄曲线拟合，对应年龄从15 Gyr到5 Gyr。我们未发现先前地面工作中观测到的光学明亮的渐近巨星分支恒星，并认为大多数这些恒星可能是拥挤效应造成的伪影。我们的结果与地面研究中发现的红外亮巨星一致，尽管它们的存在不能直接由我们的数据确认。几乎没有证据显示存在扩展或甚至红色水平分支，但我们确实发现在巨星分支自身上有一个显著的聚团。如果年龄分布不极端，则M32中的金属丰度分布比化学演化封闭盒子模型的窄得多，也似乎比太阳附近的窄一些。总体而言，M32的HST色星等图与从综合光谱指数推断出的平均光度加权年龄8.5 Gyr和[Fe/H]=-0.25一致。 显示英文摘要

摘要： We present a V-I color-magnitude diagram for a region 1'-2' from the center of M32 based on Hubble Space Telescope WFPC2 images. The broad color-luminosity distribution of red giants shows that the stellar population comprises stars with a wide range in metallicity. This distribution cannot be explained by a spread in age. The blue side of the giant branch rises to M_I ~ -4.0 and can be fitted with isochrones having [Fe/H] ~ -1.5. The red side consists of a heavily populated and dominant sequence that tops out at M_I ~ -3.2, and extends beyond V-I=4. This sequence can be fitted with isochrones with -0.2 < [Fe/H] < +0.1, for ages running from 15 Gyr to 5 Gyr respectively. We do not find the optically bright asymptotic giant branch stars seen in previous ground-based work and argue that the majority of them were artifacts of crowding. Our results are consistent with the presence of the infrared-luminous giants found in ground-based studies, though their existence cannot be directly confirmed by our data. There is little evidence for an extended or even a red horizontal branch, but we find a strong clump on the giant branch itself. If the age spread is not extreme, the distribution of metallicities in M32 is considerably narrower than that of the closed-box model of chemical evolution, and also appears somewhat narrower than that of the solar neighborhood. Overall, the M32 HST color-magnitude diagram is consistent with the average luminosity-weighted age of 8.5 Gyr and [Fe/H] = -0.25 inferred from integrated spectral indices.