Distance to the Virgo Cluster Galaxy M100 from Hubble Space Telescope Observations of Cepheids

W. L. Freedman et al.

notes:

In astronomy it is essential to know the distance to any object, because only then can the observed brightness at any wavelength be converted to the true luminosity. Variable stars called Cepheids are central to working out this "distance ladder", because their luminosity is closely related to their period and can thus be determined independently. Here Wendy Freedman and colleagues use the Hubble Space Telescope to determine the Cepheid distance to the galaxy M100, and thereby determine an accurate value for the Hubble constant, which measures the expansion rate of the Universe. This was one of the key design goals for the HST. The initial value of ~ 80 km s-1 Mpc-1 was refined over the following decade.

由哈勃空间望远镜观测造父变星到室女星系团成员星系M100的距离

弗里德曼等

在天文学中，知道任意天体的距离是重要的，因为只有这样才能将任意波长处观测到的亮度转换为真实的光度。被称作造父变星的变星对得到“距离阶梯”尤为重要，因为它们的光度和它们的光变周期紧密相关，因而它们的光度可以独立地测定。在这篇文章中，温迪弗里德曼和他的同事们利用哈勃空间望远镜测定到M100星系的造父距离，并从而测定哈勃常数(衡量宇宙膨胀率的参数)的精确值。确定哈勃常 数是哈勃空间望远镜的主要设计目标之一。它最初的值 ~ 80 km s-1 Mpc-1 在之后的几十年中得到了修正。

Implications

The HST measurement of the Cepheid distance to Ml00 enables us to place constraints on the range of plausible values of Ho and the expansion age. The current limits on Ho are illustrated in Fig. 3. Also shown in Fig. 3 are the expansion ages for various values of (Ho,  Ωo)corresponding to 14士2 Gyr. These limits are broadly consistent with estimates of the ages of globular clusters from stellar evolution theory, estimates of the age of the Galactic disk based on white dwarf cooling times, and radioactive dating of elementst.All of these age estimates generally span a full range between 10 to 18 Gyr, consistent with the lo error limits quoted above. A value of Ho= 80土17km s-1 Mpc -1 is consistent with a low- density(0.1 < Ω< 0.3) Universe and To= 12 Gyr.