arXiv 1201.10012012-01-04astro-ph.EPastro-ph.SR

关于LkCa 15周围过渡盘的性质

On the nature of the transition disk around LkCa 15

Andrea Isella, Laura M. Perez, John M. Carpenter

备注：: Accepted for publication on ApJ, 13 pages, 11 figures
DOI：: 10.1088/0004-637X/747/2/136

摘要：

我们目前的CARMA 1.3毫米连续观测的金牛座T星LkCa 15，解决了拱星尘埃连续辐射的角尺度在0.2-3角秒之间，对应于28-420 AU的距离的恒星。观测解决了尘埃排放的内部间隙，并揭示了外盘中的不对称尘埃分布。（阿布里奇）我们计算出90%的尘埃排放来自一个方位对称的环，其中包含约5 × 10 ^{-4} M_sun的尘埃。一个低表面亮度的尾巴，延伸到西北约300 AU的半径包含其余10%的观测到的连续辐射。环的表面密度在40到120天文单位之间相当平坦，而内腔在42天文单位处的1.3毫米尘埃光学深度急剧下降，或者在3到85天文单位之间向内平滑下降。（阿布里奇）。在40 AU范围内，观测到的尘埃量限制在10^{-6}到7个地球质量之间，其中最小和最大限制分别由近红外SED模拟和尘埃发射的毫米波观测确定。此外，我们证实了由尘埃和气体推断的外盘半径的差异，分别对应于150 AU和900 AU。我们不能调和这种差异，通过采用指数锥形表面密度分布的建议，为其他系统，但我们建议，在外盘的气体表面密度下降不太陡峭的模型拟合的尘埃连续排放的预测。在大于120天文单位的半径上缺乏连续辐射，这表明尘埃与气体的比率或尘埃的不透明度至少下降了5倍。我们发现，这种幅度的急剧尘埃不透明度下降是一致的径向变化的粒度分布预测现有的晶粒生长模型。

英文摘要：

We present CARMA 1.3 mm continuum observations of the T Tauri star LkCa 15,which resolve the circumstellar dust continuum emission on angular scales between 0.2-3 arcsec, corresponding to 28-420 AU at the distance of the star. The observations resolve the inner gap in the dust emission and reveal an asymmetric dust distribution in the outer disk. (Abridge) We calculate that 90% of the dust emission arises from an azimuthally symmetric ring that contains about 5x10^{-4} M_sun of dust. A low surface-brightness tail that extends to the northwest out to a radius of about 300 AU contains the remaining 10% of the observed continuum emission. The ring is modeled with a rather flat surface density profile between 40 and 120 AU, while the inner cavity is consistent with either a sharp drop of the 1.3 mm dust optical depth at about 42 AU or a smooth inward decrease between 3 and 85 AU. (Abridge). Within 40 AU, the observations constrain the amount of dust between 10^{-6} and 7 Earth masses, where the minimum and maximum limits are set by the near-IR SED modeling and by the mm-wave observations of the dust emission respectively. In addition, we confirm the discrepancy in the outer disk radius inferred from the dust and gas, which corresponds to 150 AU and 900 AU respectively. We cannot reconcile this difference by adopting an exponentially tapered surface density profile as suggested for other systems, but we instead suggest that the gas surface density in the outer disk decreases less steeply than that predicted by model fits to the dust continuum emission. The lack of continuum emission at radii lager than 120 AU suggests a drop of at least a factor of 5 in the dust-to-gas ratio, or in the dust opacity. We show that a sharp dust opacity drop of this magnitude is consistent with a radial variation of the grain size distribution as predicted by existing grain growth models.

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