Extragalactic Planetary Nebulae

根据AST-0307489的更新，门德斯博士将使用8米望远镜上的窄带成像和无缝隙光谱技术，在椭圆星系和S0星系的外围发现行星星云，并测量它们的径向速度。行星状星云代表了像我们的太阳这样的恒星生命的最后阶段。它们是由被热暴露的恒星核心电离的气体的明亮发射线来识别的；这些线也被用来测量沿视线的运动。行星状星云的分布和运动将被用来研究银河系的引力场，从而研究其暗物质含量。门德斯博士还将使用氢原子发射的亮度与氧气发射的亮度之比来估计恒星形成的气体的化学成分如何取决于离银河系中心的距离。门德斯博士和与他合作的慕尼黑团队已经研究了几个星系；一些星系没有显示出暗物质存在的证据，而另一些星系则有明确的迹象表明暗物质的存在。根据目前的提议，下一个目标是M60，这是一个扁平的星系，有一个热X射线气体光晕，它提供了一种测量该星系暗光晕质量的替代方法。其他目标星系将被选择覆盖一定范围的光度，并与另一个项目协调使用拉帕尔马(西班牙加那利群岛)上的4米赫歇尔望远镜，该望远镜只能探测到最亮的行星星云。一名研究生和一名本科生将通过参与研究进行培训。门德斯博士将开发一个网站来解释该项目，该项目将向普通公众或初级勘测课程的学生开放；该网站将涵盖从光的性质到星系周围暗物质证据的各种主题。

Under this renewal of AST-0307489, Dr. Mendez will use a technique of narrowband imaging and slitless spectroscopy on 8-meter telescopes to find planetary nebulae in the outskirts of elliptical and S0 galaxies, and measure their radial velocities. Planetary nebulae represent the final stages in the life of a star like our Sun. They are identified by the bright emission lines of gas ionized by the hot exposed stellar core; these lines are also used to measure motion along the line of sight. The distribution and motion of the planetary nebulae will be used to study the galaxy's gravitational field, and hence its dark matter content. Dr Mendez will also use the brightness ratio of emission from hydrogen atoms with that from oxygen, to estimate how the chemical composition of the gas from which the stars were formed depends on distance from the galaxy center. Dr. Mendez and the Munich group with which he collaborates have already studied several galaxies; some show no evidence for dark matter, while others have clear signatures of its presence. Under the present proposal, the next target is M60, a flattened galaxy with a halo of hot X-ray gas that provides an alternative measure of the mass of the galaxy's dark halo. Other target galaxies will be selected to cover a range in luminosity, and to coordinate with another project using the 4-meter Herschel telescope on La Palma (Canary Islands, Spain), which can detect only the brightest planetary nebulae. A graduate student and an undergraduate will be trained through their involvement in the research. Dr Mendez will develop a website explaining the project that will be accessible to the general public or students in elementary survey courses; it will cover topics ranging from the nature of light to evidence for dark matter around galaxies.