Extragalactic Planetary Nebulae

根据AST-0307489的更新，门德斯博士将在8米望远镜上使用窄带成像和无缝光谱学技术，在椭圆星系和50星系的外围寻找行星状星云，并测量它们的径向速度。行星状星云代表了像太阳这样的恒星生命的最后阶段。它们是通过被暴露在外的炽热恒星核心电离的明亮气体发射线来识别的；这些线也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星系的引力场，从而研究它的暗物质含量。门德斯博士还将利用氢原子与氧原子发射的亮度比来估计恒星形成的气体的化学成分如何取决于与星系中心的距离。门德斯博士和与他合作的慕尼黑研究小组已经研究了几个星系；一些研究没有显示暗物质存在的证据，而另一些则有暗物质存在的明确迹象。根据目前的提议，下一个目标是M60，这是一个扁平的星系，带有热x射线气体的光晕，为星系暗晕的质量提供了另一种测量方法。其他目标星系将被选择覆盖一定亮度范围，并与另一个项目协调，该项目使用位于拉帕尔马（西班牙加那利群岛）的4米赫舍尔望远镜，该望远镜只能探测到最亮的行星状星云。一名研究生和一名本科生将通过参与研究而得到训练。门德斯博士将开发一个网站来解释这个项目，这个网站将对公众或小学调查课程的学生开放；它将涵盖从光的本质到星系周围暗物质的证据等主题。

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.