Time variability of accretion, outflows and star–disk interaction in Young Stellar Objects

在它们诞生后的最初几百万年里，年轻的恒星被一个圆盘包围着，它们从圆盘中沿着磁力线吸积物质。从这样的年轻恒星天体(YSO)观察到的喷流和流出，被认为可以消除多余的角动量。星-盘环境的演化受恒星和内盘之间的磁层相互作用的调节。星-盘相互作用是一个动态过程，既有质量吸积率的内在变化，又有自转组合的星-盘-磁层-观测者系统几何构形所产生的观看效应。盘吸积的动力学和时间演化也与行星形成和迁移的时间尺度密切相关。虽然还不能用直接的成像观测来研究YSO的内盘区域，但光谱和光度学时间序列研究都有可能解开复杂的YSO现象学并建立相关的时间尺度(旋转调制、吸积区域变化、长期演化)。为此，拟议的项目将通过两个详细的案例研究和一个统计样本的试点项目来研究YSO的可变性。这些目标是在欧洲南方天文台甚大望远镜(VLT)对YSO进行的广泛光谱调查中确定的，这项供资申请的PI在其中发挥了重要作用。拟议研究的基础是PI在VLT和拉西拉上的一个小型机器人望远镜--快眼座(REM)上的客座观测站获得的观测结果。在几个小时到几年的时间尺度上使用宽带光谱和多波段测光技术，使得这些观测对于研究动态的YSO环境中尚未解释的方面具有特殊的价值。这两个详细的案例研究的主要目标是PAR-Lup3-4和TWA30AB，它们代表了临界参数空间中的基准系统(低恒星质量、较晚的盘演化阶段、有利于探测几何变化效应的高倾角)。

Throughout the first few million years following their birth, young stars are surrounded by a disk from which they accrete matter along magnetic field lines. Jets and outflows are observed from such Young Stellar Objects (YSOs), and are thought to remove excess angular momentum. The evolution of the star-disk environment is regulated by magnetospheric interactions between the star and the inner disk. The star-disk interaction is a dynamic process due to both intrinsic changes of the mass accretion rate and viewing effects produced by the geometric configuration of the star-disk-magnetosphere-observer system combined with rotation. The dynamics and time evolution of disk accretion is also intimately linked to the timescales of planet formation and migration. While the inner disk regions of YSOs where the accretion and outflow processes are operating can not be studied yet with direct imaging observations, both spectroscopy and photometric time-series studies carry the potential for disentangling the complex YSO phenomenology and establishing the relevant time-scales (rotational modulation, accretion-regime changes, secular evolution). To this effect, the proposed project will examine YSO variability with two detailed case studies and a pilot project on a statistical sample. The targets have been identified in an extensive spectroscopic survey of YSOs at the Very Large Telescope (VLT) of the European Southern Observatory in which the PI of this funding request has played a major role. The basis of the proposed study are observations obtained by the PI in Guest Observer time at the VLT and at the Rapid Eye Mount (REM), a small robotic telescope on La Silla. The use of broad-band spectroscopy and multi-band photometry on time-scales of hours to years makes these observations of exceptional value for examining as yet unexplained aspects of the dynamic YSO environment. The prime targets for the two detailed case studies, Par-Lup3-4 and TWA30AB, represent benchmark systems in critical parameter space (low stellar mass, late disk-evolution stage, high inclination favorable for detecting geometric variability effects).