题目：Elemental Compositions of Extrasolar Planetesimals -- A Unique View from Externally-Polluted White Dwarfs　　

    报告人：许偲艺（加州大学洛杉矶分校）

　　报告人简介：2006级天文系系友，目前是UCLA的PhD candidate。个人主页请参考 http://www.astro.ucla.edu/~sxu/

　　摘要：In the past few years, a large number of extrasolar planets have been detected and the next step is to better characterize these systems. Studying externally-polluted white dwarfs is a unique way to measure the elemental compositions of extrasolar planetesimals, the building blocks of planets. Observations from a handful of such stars show that extrasolar planetesimals are very similar to bulk Earth to zeroth order. (i) Oxygen, iron, silicon and magnesium are always the four most abundant elements. (ii) Volatile elements, especially carbon, are only trace constituents. We have found additional evidence that a large fraction of extrasolar planetesimals have evolved beyond simple nebular condensation. Differentiation, collisions and melting are at least as common as in our own solar system. In the end, I will review prospects for this program and opportunities with the LAMOST survey.

　　时间：10月15日（周二）上午10：00

　　地点：南京大学苏富特大厦一楼会议室

　　网站通知：http://astronomy.nju.edu.cn/doctorforum/

欢迎各位老师、同学参加！

　　                                      南京大学天文与空间科学学院