32 HZ Around Other Main Sequence Stars The same type of HZ calculations both on

32 hz around other main sequence stars the same type

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3.2 HZ Around Other Main Sequence Stars The same type of HZ calculations, both on the base of climatic constraints and on the base of Earth system modeling as well, can be performed for stars with masses differ- ent from the solar mass. Kasting et al. [13] restricted themselves to stellar lifetimes greater than 2 Ga which corresponds to masses less than 1.5 M s (1 M s = one solar mass). At the low-mass end they restricted themselves to masses greater than 0.5 M s , because stars with masses 0.5 M s show negligible evolution. Stellar luminosities and temperatures were taken directly from Iben [29, 30], climatic constraints correspond to their so-called interme- diate case. As expected, stellar HZ‘s for more massive stars are rather short, because they have to be truncated at the end of the main sequence. HZ‘s for low mass stars are essentially the same over time. In Fig. 3.2 we show the so-called zero age main se- quence HZ from Kasting et al. [13] as function of stellar mass. In our calculation of HZ in extrasolar planetary systems [8] we used the luminosity evolution of central stars on the main sequence in the mass range between 0.8 and 2.5 M s . The results have been obtained by polynomial fitting of detailed stellar evolution models like the one presented by Schaller et al. [31]. The temperature tolerance win- dow for the biological productivity given in Eq. (3.3) was extended to the range be-
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