Massive Compact Dust Disk with a Gap around CW Tau Revealed by ALMA Multiband Observations
Massive Compact Dust Disk with a Gap around CW Tau Revealed by ALMA Multiband Observations
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DOI：
10.3847/1538-4357/ac634d
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发表时间：
2022-03
期刊：
影响因子：
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通讯作者：
T. Ueda;A. Kataoka;T. Tsukagoshi
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作者：
T. Ueda;A. Kataoka;T. Tsukagoshi
半径为≲50 Au的致密原行星盘在年轻的小质量恒星周围很常见。我们报告了高分辨率的ALMA尘埃连续谱观测，观测到CW Tau周围的一个致密盘的波段4(λ=2.2 mm)、6(1.3 mm)、7(0.89 mm)和8(0.75 mm)。光谱能量分布在0.75~1.3 mm之间为2.0±0.24，在2.17~3.56 mm之间为3.7±0.29。在2.17-3.56 mm之间的陡峭斜率与来自小颗粒的光学薄发射(≲350μm)的斜率一致。我们对ALMA数据进行了参数拟合，以表征尘埃盘。有趣的是，如果尘气质量比为0.01时，Toomre Q参数达到∼1-3，这表明CW Tau盘可能存在轻微的引力不稳定。总尘埃质量估计为∼250M⊕，根据先前的波段7偏振观测推断，最大尘埃尺寸为140Mμm，即使是较大的颗粒尺寸，也至少为80M⊕。这一结果表明，尽管CW Tau盘很小，但它是相当大的。此外，我们清楚地确定了位于∼20Au的带隙结构，该结构可能是由一颗巨行星引起的。尽管有这些有趣的特征，CW Tau光盘在ALMA波段6处具有正常的光盘光度、大小和光谱指数，这可能是解决II类光盘质量预算问题的线索。
Compact protoplanetary disks with a radius of ≲50 au are common around young low-mass stars. We report high-resolution ALMA dust continuum observations toward a compact disk around CW Tau at Bands 4 (λ = 2.2 mm), 6 (1.3 mm), 7 (0.89 mm), and 8 (0.75 mm). The spectral energy distribution shows the spectral slope of 2.0 ± 0.24 between 0.75 and 1.3 mm, while it is 3.7 ± 0.29 between 2.17 and 3.56 mm. The steep slope between 2.17 and 3.56 mm is consistent with that of optically thin emission from small grains (≲350 μm). We perform parametric fitting of the ALMA data to characterize the dust disk. Interestingly, if the dust-to-gas mass ratio is 0.01, the Toomre Q parameter reaches ∼1–3, suggesting that the CW Tau disk might be marginally gravitationally unstable. The total dust mass is estimated as ∼250 M ⊕ for the maximum dust size of 140 μm that is inferred from the previous Band 7 polarimetric observation and at least 80 M ⊕ even for larger grain sizes. This result shows that the CW Tau disk is quite massive in spite of its smallness. Furthermore, we clearly identify a gap structure located at ∼20 au, which might be induced by a giant planet. In spite of these interesting characteristics, the CW Tau disk has normal disk luminosity, size, and spectral index at ALMA Band 6, which could be a clue to the mass budget problem in Class II disks.