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arXiv 2410.06207astro-ph.EPastro-ph.SR
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引力不稳定性临界点处原行星盘的尘埃漂移时标

Dust Drift Timescales in Protoplanetary Disks at the Cusp of Gravitational Instability

Jonathan P. Williams, Caleb Painter, Alexa R. Anderson, Alvaro Ribas

AI总结:

本研究通过对比ALMA毫米波段观测的原行星盘半径,发现处于引力不稳定性临界点的盘尘埃漂移时标与恒星寿命相当,同时解决了尘埃寿命和系外行星质量预算两大难题。

摘要:

毫米波段发射辐射的尘埃颗粒尺寸使其易在原行星盘中发生漂移,这是由尘埃与气体的轨道速度差异导致的。特征漂移时标取决于气体面密度。通过对比ALMA在毫米波段的CO谱线观测和连续谱观测得到的盘半径测量结果,可以自洽地确定气体面密度分布和尘埃漂移时间。我们发现,与测得尘埃质量相匹配的分布具有极短的漂移时标,比恒星年龄短一个数量级甚至更多;而处于引力不稳定性临界点(通过Toomre参数最小值Qmin~1-2定义)的盘,其漂移时标与恒星寿命相当。这一结论适用于尘埃质量大于5倍地球质量(5 MEarth)的盘,覆盖的绝对年龄范围从不足1 Myr到超过10 Myr。推断得到的盘质量与恒星质量呈标度关系:Mdisk ~ Mstar / 5Qmin。这种对气体和尘埃盘尺寸的解释同时解决了两个长期存在的问题——尘埃寿命问题和系外行星质量预算问题,并表明我们可以将毫米波段观测作为一个窗口,用以研究处于长期演化中的、具有宽尺寸分布的底层粒子群,这些粒子与大质量星子盘共存。

英文摘要:

Millimeter emitting dust grains have sizes that make them susceptible to drift in protoplanetary disks due to a difference between their orbital speed and that of the gas. The characteristic drift timescale depends on the surface density of the gas. By comparing disk radii measurements from ALMA CO and continuum observations at millimeter wavelengths, the gas surface density profile and dust drift time can be self-consistently determined. We find that profiles which match the measured dust mass have very short drift timescales, an order of magnitude or more shorter than the stellar age, whereas profiles for disks that are on the cusp of gravitational instability, defined via the minimum value of the Toomre parameter, Qmin ~ 1-2, have drift timescales comparable to the stellar lifetime. This holds for disks with masses of dust > 5 MEarth across a range of absolute ages from less than 1 Myr to over 10 Myr. The inferred disk masses scale with stellar mass as Mdisk ~ Mstar / 5Qmin. This interpretation of the gas and dust disk sizes simultaneously solves two long standing issues regarding the dust lifetime and exoplanet mass budget and suggests that we consider millimeter wavelength observations as a window into an underlying population of particles with a wide size distribution in secular evolution with a massive planetesimal disk.

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