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.
由哈勃空間望遠(yuǎn)鏡觀測造父變星到室女星系團(tuán)成員星系M100的距離
弗里德曼等
在天文學(xué)中确封，知道任意天體的距離是重要的昏名，因為只有這樣才能將任意波長處觀測到的亮度轉(zhuǎn)換為真實的光度陨瘩。被稱作造父變星的變星對得到“距離階梯”尤為重要，因為它們的光度和它們的光變周期緊密相關(guān)，因而它們的光度可以獨立地測定丙号。在這篇文章中乏梁，溫迪弗里德曼和他的同事們利用哈勃空間望遠(yuǎn)鏡測定到M100星系的造父距離，并從而測定哈勃常數(shù)(衡量宇宙膨脹率的參數(shù))的精確值似炎。確定哈勃常 數(shù)是哈勃空間望遠(yuǎn)鏡的主要設(shè)計目標(biāo)之一辛萍。它最初的值 ~ 80 km s-1 Mpc-1 在之后的幾十年中得到了修正。
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.
