RUI: A Detailed Study of the Circumstellar Environment Around Neaby A-Type Stars: Possible Planet Construction Zones

摘要：本研究项目的目的是评估在我们的太阳系附近的“绘面星β现象”的频率，并通过对绘面星β系统的详细光谱研究来深入了解“行星系统的形成过程”。多年来，天文学家一直在寻找太阳系外的其他行星。他们特别想研究正在经历行星形成过程的系统，这样他们就可以深入了解我们太阳系的起源。最好的候选者是绘架星β，这是一颗附近的a型恒星，被巨大的尘星盘和非常动态的星周气体环境所包围。有人提出，绘架星β系统中星周气体吸收成分的短期变化可能是由于彗星大小的天体的蒸发。也有人认为，绘人族β周围的巨大尘埃盘可能是我们柯伊伯带的一个类似物，柯伊伯带是海王星轨道之外的一个区域，现在被认为是短周期彗星的来源。对附近A型恒星的星周环境进行了详细的光谱研究。计划恒星是年轻的a型恒星，可以作为研究行星盘清理阶段气体吸积的实验室。目标是表征这些恒星周围的碎片盘。在距离太阳25秒差距内的62颗A型恒星中，一项天空体积有限的搜索已经完成。初步研究包括两项独立研究：一项是利用IRAS卫星数据获取星周尘埃数据，另一项是利用高分辨率可见光和紫外光谱获取星周气体数据。研究发现，超过18%的恒星都有星周尘埃，有十几颗恒星都有星周气体。对这些恒星的进一步监测表明，其中至少有四颗恒星具有类似于绘架星β的可变光谱特征，表明有气体进入。四颗恒星中的一颗被确定为具有可变的星周气体特征，并且在IRAS微弱源调查检测极限下没有尘埃特征。我们将开展更多对类绘形行星系统的研究，为我们理解行星系统的形成提供重要的约束条件。通过分析高信噪比和高分辨率的可见光和紫外波长光谱，可以识别出更多附近有类似于绘人猿β星的星周气体的a星。通过监测在高分辨率钙离子K和钠离子D波长光谱中观测到的时间和可变的星周吸收谱线组分，将对所有类绘形星β系统的动力学进行研究。这项研究将有助于更好地理解星周气体和尘埃之间的相互关系。最终，将编制星周尘埃和气体特性的地图集；即所有附近a型恒星的质量、密度、温度分布、速度场和化学梯度。这些物理条件，特别是在类绘形星β系统中的物理条件，将为吸积和行星系统形成模型提供有价值的约束。这张地图集将是第一次全面汇编所有附近a型恒星周围的星周尘埃和气体的特性，使用来自IRAS、HST、IUE卫星数据以及地面数据的数据。该地图集将通过期刊出版物提供给一般天文团体，而地面数据（在基特峰国家天文台、塞罗·托洛洛国际天文台、麦克唐纳天文台和斯特罗姆洛山天文台获得的150多个夜晚的观测数据）将通过互联网提供。

Abstract K. P. Chang AST 98-19737The objectives of this research project are to assess the frequency of the "Beta Pictoris phenomenon" in our solar neighborhood, and to gain more insight into the "planetary system formation process" through detailed spectroscopic studies of Beta Pictoris-like systems.For years, astronomers have been searching for other planets outside our Solar System. They especially want to study systems that are undergoing the process of planet formation so that they can gain insight into the origin of our own Solar System. The best candidate is Beta Pictoris, a nearby A type star surrounded by a huge dust disk and a very dynamic circumstellar gas environment. It has been suggested that the short-term variations of circumstellar gas absorption components in the Beta Pictoris system could be due to the evaporation of comet-size bodies. It also has been suggested that the huge dust disk around Beta Pictoris could be an analog of our Kuiper Belt, a region past the orbit of the planet Neptune that is now considered to be the source of short-period comets.A detailed, spectroscopic study of the circumstellar environments of nearby A-type stars has been carried out. The program stars are young A-type stars that could serve as laboratories for the study of gas accretion during the clearing phase of planetary disks. The goal has been to characterize the debris disks around these stars. A sky volume-limited search for Beta Pictoris-like systems among the 62 A-stars within 25 parsecs of the Sun has been completed. The preliminary search consisted of two independent studies: one to obtain data on circumstellar dust using the IRAS satellite data and the second one for data on the circumstellar gas using high-resolution visual and ultraviolet spectra. It was found that more than 18% of the stars have circumstellar dust, and more than a dozen stars with circumstellar gas have been identified. Further monitoring of the stars has revealed that at least four of these have Beta Pictoris-like variable spectral signatures indicating gaseous infall. One of the four stars is identified to have variable circumstellar gas features and has no dust signature at the IRAS Faint Source Survey detection limit. More studies of Beta Pictoris-like systems will be carried out to provide important constraints for our understanding of planetary system formation.Analyzing high signal-to-noise and high-resolution visual and ultraviolet wavelength spectra will identify more nearby A-stars that have circumstellar gas similar to Beta Pictoris. A study of the dynamics in all the Beta Pictoris-like systems will be carried out by monitoring the temporal and variable circumstellar absorption line components observable in high-resolution Calcium II K and Sodium I D wavelength spectra. This study will lead to a better understanding of the inter-relationship between the circumstellar gas and dust. Ultimately, an atlas will be compiled of the circumstellar dust and gas properties; namely mass, density, temperature distributions, velocity fields, and chemical gradients for all the nearby A-type stars. These physical conditions, especially those in the Beta Pictoris-like systems, will provide valuable constraints for models of accretion and planetary system formation. This atlas will be the first thorough compilation of the properties of circumstellar dust and gas around all the nearby A-type stars using data from the IRAS, HST, IUE satellite data, in addition to ground-based data. The atlas will be available to the general astronomical community through journal publications, and the ground-based data (150 plus nights of observations obtained at Kitt Peak National Astronomy Observatory, Cerro Tololo International Observatory, McDonald Observatory, and Mt. Stromlo Observatory) will be made available via the Internet.