1. 【题目】 All the metals made by a star through nuclear syntheses will be trapped in the core by its own strong gravitational potential. We will never see absorption lines of metals in any stellar spectra. All the metals (A > 4) on the Earth should be made at the moment when the Universe was created and have nothing to do with what stars are doing. 【瓶颈】 查过 Carroll & Ostile 的书，和资料了，还是找不出哪里不正确... 2. 【题目】 Speaking of a similar phenomenon, a fantastic planetary nebula (PN) appears as a glowing circular ring around its central relic star, i.e. a white dwarf. PNe should be expanding "rings" of hot gas in the space. 【瓶颈】 这是一题反证题，planetary nebula 很明显不是"ring" ，可是题目有说不能 单纯说哪里不对，要用反证法说如果XX成立，则...，实在没有头绪 3. 【题目】 I know those dark lines in the solar (or stellar) spectrum. They are absorption lines caused by molecules above the photosphere, whose emission is characterized by a blackbody radiation at Te = 5777 K. Similarly,emission lines in the solar spectrum must come from molecules ""below"" the photosphere. 【瓶颈】这题也知道不是"below",可是怎麽反证又难倒小弟了... 因为很少写关系，实在不太会反证法，也许是太习惯只有算式的题目了吧...想想真是 惭愧 不好意思，问题有点多，麻烦各位前辈了，感恩! --

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