A Study of Proto-Planetary System Candidates

我们太阳系的起源是天体物理学中最基本的问题之一。研究这个问题的一种方法是研究仍处于行星形成阶段的系统。对绘架星β (A5 IV-V)的深入研究揭示了恒星周围的尘埃盘和动态气体包层（显示质量下降和流出）。β Pic的年龄（2亿年）大致对应于行星形成和随后的太阳系“重轰炸”时代。因此，β Pic的尘埃+气体盘很可能类似于原始太阳星云中的吸积盘。然而，仍然没有解决为什么β - Pic似乎有这样一个动态的尘埃+气体盘，每年大约有100-200个大质量坠落事件。对于β - Pic的吸积机制，以及碎片盘和它的星周气体之间的关系的理解，还远远没有完成。这是一个仍处于形成阶段的年轻行星系统，还是处于清理阶段的尘埃原恒星吸积盘的残余？其他类似于Beta Pic的系统，有碎片盘和星周气体，需要识别和研究才能回答这些问题。探测到附近A型恒星周围的星周碎片，比如β - Pic，提供了一个无与伦比的机会来探索可能的原行星系统，这些系统可能类似于我们早期进化阶段的太阳系。因此，对原行星系统候选者的搜索将完成。对这些系统进行研究的最终目的是确定它们作为一个整体是否代表了行星形成的某个阶段。主要有三个目标：(1)利用红外天文卫星（IRAS）微弱源巡天（FSS）数据识别附近有星周尘埃的主序A型恒星。虽然通过直接成像很难探测到尘盘，但人们可以通过探测到与轨道颗粒的热辐射相一致的过量红外波长发射来推断星周尘埃的存在。(2)获得体积有限的a星样品的高分辨率可见光和紫外波长光谱，以研究星周气体的存在、电离和运动学。这些高分辨率光谱可以用来探测狭窄的星周气体吸收光谱特征，并推断出视线内的星周气体量。可见和紫外波长的星周吸收线将相互比较，以测试是否彗星类天体的蒸发导致了在体积有限的a星调查中，在β Pic和其他几颗β Pic类恒星的光谱中看到的可变红移线。(3)验证在这些候选行星系统的碎片盘的内部区域发生气体吸积的假设。这些系统可能具有与原始太阳星云相似的物理特性。对这些原行星系统的星周环境的动态性质的研究将为行星系统的形成提供有价值的见解。

9520989 Cheng The origin of our own solar system is one of the most fundamental problems in astrophysics. One way to investigate this problem is to study systems that are still in the phase of planet formation. Intensive studies of Beta Pictoris (A5 IV-V) have revealed a dust disk and a dynamic gas envelope (showing both mass infall and outflow) around the star. The age of Beta Pic (200 million years) roughly corresponds to the era of planet formation and subsequent "heavy bombardment" in our solar system. Therefore, it is likely that Beta Pic's dust + gas disk is similar to the accretion disk in the primordial solar nebula. However, it is still not resolved why Beta Pic seems to have such a dynamic dust + gas disk, with about 100-200 mass infall events each year. The understanding of the accretion mechanism in Beta Pic, and of the relationship between the debris disk and its circumstellar gas, is far from complete. Is this a young planetary system still undergoing formation, or is it the remnant of a dusty proto-stellar accretion disk in its clearing phase? Other systems similar to Beta Pic with debris disks and circumstellar gas need to be identified and studied to answer the questions. The detection of circumstellar debris around nearby A type stars, such as ,Beta Pic, provides an unparalleled opportunity to explore possible proto-planetary systems that could resemble our own Solar System at an early stage of evolution. Therefore, a search for proto-planetary system candidates will be completed. The ultimate goal of this study of these systems is to ascertain if they, as a group, represent some phase of planet formation. Three major objectives will be pursued: (1) Identify nearby main-sequence A type stars that have circumstellar dust, using the Infrared Astronomical Satellite (IRAS) Faint Source Survey (FSS) data. Although it is very difficult to detect dust disks by direct imaging, one can infer the presence of circumstellar dust by the det ection of excess infrared wavelength emission that is consistent with thermal radiation from the orbiting grains. (2) Obtain high-resolution visible and ultraviolet wavelength spectra of the volume-limited A-star sample to study the presence, ionization, and kinematics of the circumstellar gas. These high-resolution spectra can be used to detect narrow circumstellar gas absorption spectra features and the amount of circumstellar gas in the line of sight will be inferred. The visible and ultraviolet wavelength circumstellar absorption lines will be compared to each other to test whether the evaporation of cometary-like bodies is responsible for the variable redshifted lines seen in spectra of Beta Pic and several other Beta Pic-like stars in the volume-limited A-star survey. (3) Test the hypothesis that gaseous accretion is occurring in the inner regions of the debris disks of these planetary system candidates. These systems might have physical properties similar to those of the primordial solar nebula. The study of the dynamic nature of these proto-planetary system's circumstellar environments will provide valuable insight into the formation of planetary systems.