Understanding the Boundary Between Stars and Substellar Objects in the Solar Neighborhood

Sergio迪特里希博士被授予NSF天文学和天体物理学博士后奖学金，在华盛顿卡内基研究所地磁系开展研究和教育计划。棕矮星是在形成过程中从未获得足够质量的物体，以达到点燃持续的氢核聚变所需的内部温度和压力，这是恒星物体的标志。了解极低质量恒星和褐矮星之间的边界对于在宇宙中寻找生命具有深远的意义。生命很可能在绕恒星运行的行星上进化，但由于褐矮星系统不断变化的温度，生命很难在褐矮星系统上进化。迪特里希博士研究恒星/亚恒星边界附近物体的温度、半径和光度的趋势。他的论文工作确定了恒星和亚恒星人口的基础上，这些趋势。这项工作现在将扩展到更大的恒星样本，并将探索不同恒星的化学成分如何改变这一边界。迪特里希博士将利用他作为前初中和高中物理科学教师的经验，促进天文学在高中物理课程中的整合。他将编写一本活动书，作为物理教师的资源，他们希望通过天文学的例子来说明物理概念来丰富他们的课程。迪特里希博士将在他的研究期间解决以下三个科学问题：（1）什么是恒星/亚恒星边界的光度函数？(2)金属丰度如何影响质量接近氢燃烧最小质量的物体的性质？（3）如何利用已知动力学质量的天体在恒星/亚恒星边界建立一个更可靠、更详细的质量-光度关系？卡内基智利拉斯坎帕纳斯天文台的独特资源是回答这些问题的关键。由于精确的距离测量对于确定光度和半径至关重要，迪特里希博士和合作者将使用杜蓬特2.5米望远镜上的卡内基天体测量行星搜索相机（CAPSCam）来确定精确的三角测量，以使研究样本体积完整。还将使用几台Las Campanas望远镜对这些非常微弱的天体进行光学测光，这对于计算热辐射通量是必要的。样品的金属丰度将通过麦哲伦6.5米望远镜的光谱观测来确定。麦哲伦II号望远镜上的MagAO自适应光学系统是能够获得光波长衍射极限图像的仅有的地面系统之一。这一独特的能力将用于对动力质量已知的近距离双星系统中的恒星进行光度测定。解析后的光学测光将用来确定这些恒星的光度和有效温度，从而建立质量-光度关系。

Dr. Sergio Dieterich is awarded an NSF Astronomy and Astrophysics Postdoctoral Fellowship to carry out a program of research and education at the Department of Terrestrial Magnetism of the Carnegie Institution of Washington. Brown dwarfs are objects that never acquired enough mass during their formation to attain the internal temperature and pressure necessary to ignite the sustained nuclear fusion of hydrogen, which is the hallmark of a stellar object. Understanding the boundary between very low mass stars and brown dwarfs has deep implications for the search for life in the Universe. It is likely that life may evolve on planets orbiting stars but it is more difficult for life to evolve on brown dwarf systems due to their constantly changing temperature. Dr. Dieterich studies trends in temperature, radius, and luminosity of objects near the stellar/substellar boundary. His thesis work identified a stellar and a substellar population based on these trends. This work will now be extended to a larger sample of stars, and will explore how chemical compositions for different stars change this boundary. Dr. Dieterich will use his experience as a former middle and high school physical science teacher to facilitate the integration of astronomy in the high school physics curriculum. He will compile an activity book that will serve as a resource for physics teachers who wish to enrich their classes by illustrating physical concepts with examples from astronomy. Dr. Dieterich will address the following three scientific questions during his fellowship: (1) What is the luminosity function at the stellar/substellar boundary? (2) How does metallicity affect the properties of objects with masses close to the hydrogen burning minimum mass? and (3) How can we use objects with known dynamical masses to create a more robust and detailed Mass-Luminosity Relation at the stellar/substellar boundary? The unique resources of Carnegie's Las Campanas Observatory in Chile are key to answering these questions. Because an accurate distance measurement is essential for establishing luminosity and radius, Dr. Dieterich and collaborators will use the Carnegie Astrometric Planet Search Camera (CAPSCam) on the du Pont 2.5 meter telescope to determine precise trigonometric parallaxes so as to make the study sample volume-complete. Several Las Campanas telescopes will also be used to obtain optical photometry for these very faint objects, which is necessary for calculating bolometric fluxes. Metallicities for the sample will be established through spectroscopic observations done with the Magellan 6.5 meter telescopes. The MagAO adaptive optics system on the Magellan II telescope is one of the only ground based systems capable of obtaining diffraction-limited images in optical wavelengths. This unique capability will be used for the photometric characterization of stars in close binary systems for which dynamical masses are known. The resolved optical photometry will then be used to determine luminosity and effective temperature for these stars, therefore populating the mass-luminosity relation.