Variability of the transitional T Tauri star T Chamaeleontis
Variability of the transitional T Tauri star T Chamaeleontis
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DOI：
10.1051/0004-6361/200811073
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发表时间：
2009-04
影响因子：
6.5
通讯作者：
E. Schisano;E. Covino;J. Alcalá;M. Esposito;D. Gandolfi;E. Guenther
中科院分区：
文献类型：
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作者：
E. Schisano;E. Covino;J. Alcalá;M. Esposito;D. Gandolfi;E. Guenther
上下文众所周知，对于太阳质量的恒星来说，行星的形成始于一个拱星盘。对过渡天体的研究表明，它们的星盘有明显的演化迹象，如尘埃颗粒的生长和星盘开始分散，这对于理解尘埃颗粒凝聚和行星形成的开始的过程至关重要。目标。我们试图解释的物理性质的T Chamaeleontis，一个过渡的T金牛座星星显示UX猎户座型的变化，其相关的光盘，并探讨可能的影响，光盘清除过程。方法.不同的光谱诊断进行了检查，基于丰富的光学高分辨率和低分辨率光谱的集合。利用互相关技术确定了光球的径向速度和投影速度，通过对互相关剖面应用二等分法分析了光球谱线的形状变化，并计算了Li i λ6708 A光球吸收谱线和最显著发射谱线（例如，Hα、H β和[Oi] 6300 A）。在主要的排放特征的变异性进行了检查，通过线轮廓相关矩阵。现有的光学和近红外测光与来自公共目录的红外数据相结合，用于构建光谱能量分布（SED）和推断基本的恒星和光盘的属性。结果主要发射谱线Hα从纯发射到接近光球吸收的时间尺度上的显著变化与超过3个量级的视消光变化相关，而光球吸收谱没有显示出大的变化。Hα和Hβ的发射强度是高度可变的，并且与[Oi]线的发射强度有很好的相关性。Hα谱线轮廓的结构在每天的时间跨度上也是变化的，而没有连续性面纱表明质量吸积非常低或没有。星星径向速度的变化可以在类似的时间尺度上测量到，但没有明显的周期性。SED建模证实了光盘中存在间隙。结论.变量拱星消光被推断为负责观测到的恒星连续通量的显着变化和伴随的变化，在发射功能的对比度效应。星团结构，包含大的尘埃颗粒和轨道的星星在几十个Au单位，模糊的星星，并最终，部分内部的拱星区，而大部分的氢线发射区和外部低密度风区跟踪的[Oi]保持不受影响。与这种情况相一致的是，探测到的径向速度变化也可以用星团物质过境和部分遮蔽星星来解释。
Context. It is known that for solar-mass stars planet formation begins in a circumstellar disc. The study of transitional objects exhibiting clear signs of evolution in their discs, such as the growth of dust particles and beginning of disc dispersal, is fundamental to understanding the processes governing dust-grain coagulation and the onset of planet formation. Aims. We attempt to characterise the physical properties of T Chamaeleontis, a transitional T Tauri star showing UX Ori-type variability, and of its associated disc, and probe the possible effects of disc-clearing processes. Methods. Different spectral diagnostics were examined, based on a rich collection of optical high- and low-resolution spectra. The cross-correlation technique was used to determine radial and projected rotational velocities, shape changes of photospheric lines were analysed via bisector-method applied to the cross-correlation profile, and the equivalent widths of both the Li i λ6708 A photospheric absorption and the most prominent emission lines (e.g., Hα ,H β and [Oi] 6300 A) were measured. Variability in the main emission features was inspected by means of line-profile correlation matrices. Available optical and near-infrared photometry combined with infrared data from public catalogues was used to construct the spectral energy distribution (SED) and infer basic stellar and disc properties. Results. Remarkable variability on timescale of days in the main emission lines, Hα changing from pure emission to nearly photospheric absorption, is correlated with variations in visual extinction of over three magnitudes, while the photospheric absorption spectrum shows no major changes. The strength of emission in Hα and Hβ is highly variable and well correlated with that of the [Oi] lines. The structure of the Hα line-profile also varies on a daily time-span, while the absence of continuum veiling suggests very low or no mass accretion. Variations of up to nearly 10 km s −1 in the radial velocity of the star are measured on analogous timescales, but with no apparent periodicity. SED modelling confirms the existence of a gap in the disc. Conclusions. Variable circumstellar extinction is inferred to be responsible for the conspicuous variations observed in the stellar continuum flux and for concomitant changes in the emission features by contrast effect. Clumpy structures, incorporating large dust grains and orbiting the star within a few tenths of AU, obscure episodically the star and, eventually, part of the inner circumstellar zone, while the bulk of the hydrogen-line emitting-zone and outer low-density wind region traced by the [Oi] remain unaffected. In agreement with this scenario, the detected radial velocity changes are also explainable in terms of clumpy material transiting and partially obscuring the star.