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arXiv 2106.02064astro-ph.SR
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用K2观察金牛座的北斗七星群

The dipper population of Taurus seen with K2

Noemi Roggero, Jérôme Bouvier, Luisa M. Rebull, Ann Marie Cody

发表信息：
A&A 651, A44 (2021)
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摘要：

斗星是典型的低质量，主序前的恒星，在它们的光变曲线中显示出下降。这些下降被归因于在圆盘内部形成的尘埃翘曲。我们的目标是推导出金牛座北斗星的性质，以评估诱导北斗光变曲线的物理机制。我们利用K2、C4和C13的光变曲线从金牛座恒星形成区的179个成员和可能的成员中选择了一个勺形样本。我们将周期图与小波分析相结合，研究了恒星的周期性，并从测光结果中得到了恒星的参数。我们还研究了光度下降的形态。我们发现，在我们用K2观测到的带盘恒星中，约30%的北斗星出现在我们的视觉上。这代表了它们真实发生的下限。大约有一半的勺形是非周期性的，其中大多数是由另一种类型的变化。所选择的样品是晚光谱型（K/M），低质量和中等质量吸积率，并有几天的周期。我们观察到一个短暂的北斗七星在几个旋转周期和一个变化的周期。倾角的结构可以是复杂的，并且在一个恒星旋转的时间尺度上变化很大。共转半径位于几个恒星半径处，并且共转时的温度允许尘埃存活。许多系统被认为是在中度到高度倾斜。我们发现，尘埃结构产生的倾角的角度延伸与恒星周期。磁层吸积导致吸积柱及其底部遮蔽恒星，可以解释大多数观测到的光变曲线。虽然与该模型兼容，但许多恒星的倾角都是中等的，并且不排除由内部盘弯曲引起的掩星机制，以解释北斗光变。

英文摘要：

Dippers are typically low-mass, pre-main-sequence stars that display dips in their light curves. These dips have been attributed to dusty warps that form in the inner part of the disk. Our goal is to derive the properties of dipper stars in Taurus to assess the physical mechanisms that induce dipper light curves. We used the light curves of K2 C4 and C13 to select a dipper sample among 179 members and possible members of the Taurus star-forming region based on the light-curve morphology. We studied the periodicities by combining periodograms with wavelet analysis and derived the stellar parameters from the photometry. We also studied the morphology of the photometric dips. We find a dipper occurrence of ~30% in disk-bearing stars observed with K2 that were identified visually by us. This represents a lower limit to their true occurrence. About half of the dippers are aperiodic, and most of these are dominated by another type of variability. The chosen sample is of late spectral type (K/M), low mass and moderate mass accretion rates and has periods of a few days. We observed a transient dipper over a few rotation cycles and a dipper with a changing period. The structure of the dips can be complex and varies strongly over timescales of down to one stellar rotation. The corotation radii are located at a few stellar radii, and the temperatures at corotation allow dust survival. Many of the systems are seen at moderate to high inclination. We find that the angular extension of the dusty structure producing the dips is correlated with the stellar period. Magnetospheric accretion, which causes an accretion column and its base to occult the star, can explain most of the observed light curves. Although compatible with the model, many of the stellar inclination angles are moderate and do not exclude mechanisms other than the occultation by an inner disk warp to account for dipper light curves.

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