A Rotation Rate for the Planetary-mass Companion DH Tau b
A Rotation Rate for the Planetary-mass Companion DH Tau b
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DOI：
10.3847/1538-3881/ab67c4
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发表时间：
2020-01
期刊：
影响因子：
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通讯作者：
J. Xuan;M. Bryan;H. Knutson;B. Bowler;C. Morley;B. Benneke
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文献类型：
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作者：
J. Xuan;M. Bryan;H. Knutson;B. Bowler;C. Morley;B. Benneke
DHTau b是一颗年轻的行星质量的伴星，它的轨道与它的∼2 Myr老主星DHTau的预计距离为320Au。据估计，这个天体的质量在8-22之间，跨越了氢燃烧的极限，可能是通过核心或卵石吸积、圆盘不稳定或分子云碎裂而形成的。为了阐明DHTau b的形成历史，我们首次使用KECK/NIRSpec的高分辨率(R∼25,000)近红外光谱测量了该天体的旋转线展宽。我们测得的投影自转速度(V Sin I)为9.6±0.7千米S−1，对应的自转速度介于DHTaob预测的破裂速度的9%到15%之间。这种低的自转速度很好地符合这样的情景，即在吸积后期，伴星与其绕行星盘之间的磁耦合降低了角动量并调节了自转。我们将DHTau b的自转速度与其他质量在0.3到20之间的行星质量天体的公开值进行了比较，没有发现在这个质量区域内质量和自转速度之间存在关联的证据。最后，我们搜索了DHTau b光谱中单个分子的证据，发现它主要是CO和H2O，没有CH4存在的证据。考虑到DHTau b的有效温度相对较高(∼2300K)，这与预期相符。
DH Tau b is a young planetary-mass companion orbiting at a projected separation of 320 au from its ∼2 Myr old host star DH Tau. With an estimated mass of 8–22 this object straddles the deuterium-burning limit, and might have formed via core or pebble accretion, disk instability, or molecular cloud fragmentation. To shed light on the formation history of DH Tau b, we obtain the first measurement of rotational line broadening for this object using high-resolution (R ∼ 25,000) near-infrared spectroscopy from Keck/NIRSPEC. We measure a projected rotational velocity (v sin i) of 9.6 ± 0.7 km s−1, corresponding to a rotation rate that is between 9% and 15% of DH Tau b’s predicted breakup speed. This low rotation rate is in good agreement with scenarios in which magnetic coupling between the companion and its circumplanetary disk during the late stages of accretion reduces angular momentum and regulates spin. We compare the rotation rate of DH Tau b to published values for other planetary-mass objects with masses between 0.3 and 20 and find no evidence of a correlation between mass and rotation rate in this mass regime. Finally, we search for evidence of individual molecules in DH Tau b’s spectrum and find that it is dominated by CO and H2O, with no evidence of the presence of CH4. This agrees with expectations given DH Tau b’s relatively high effective temperature (∼2300 K).