Obliquity Constraints on an Extrasolar Planetary-mass Companion
Obliquity Constraints on an Extrasolar Planetary-mass Companion
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DOI：
10.3847/1538-3881/ab76c6
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发表时间：
2020-02
期刊：
影响因子：
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通讯作者：
M. Bryan;E. Chiang;B. Bowler;C. Morley;S. Millholland;S. Blunt;Katelyn B. Ashok;E. Nielsen
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文献类型：
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作者：
M. Bryan;E. Chiang;B. Bowler;C. Morley;S. Millholland;S. Blunt;Katelyn B. Ashok;E. Nielsen
我们首先对太阳系外行星质量伴星的倾斜度进行了限制。我们的目标是直接成像的系统2MASS J01225093-2439505(2M0122)，它由一颗120-0.4M的⊙星组成，在50Au的位置上有一颗12-27 MJ的伴星。我们约束了系统的所有三个角动量矢量：伴星自旋轴、恒星自旋轴和轨道法线相对于我们的视线是如何倾斜的。为了实现这一点，我们使用凯克天文台的NIRSpec的新的近红外高分辨率光谱来测量恒星和伴星的投影自转速度(V Sin I)。我们将其与TESS的新恒星光度自转周期和哈勃太空望远镜公布的伴随自转周期相结合，得到了两个天体的自旋轴倾角。我们还拟合了多个天体测量时期，包括一次新的NIRC2/Keck观测，以测量2M0122b的轨道倾斜度。三个视线倾角限制了真实的非投影伴星倾角和恒星倾角。我们发现，虽然恒星倾角略微倾向于对齐，但伴星倾角暂时倾向于不对齐。我们评估可能的起源场景。虽然碰撞、长期自旋轨道共振和Kozai-Lidov振荡不太可能发生，但由引力湍流圆盘中的引力不稳定形成的情况似乎很有希望。
We place the first constraints on the obliquity of a planetary-mass companion outside of the solar system. Our target is the directly imaged system 2MASS J01225093–2439505 (2M0122), which consists of a 120 Myr 0.4 M⊙ star hosting a 12–27 MJ companion at 50 au. We constrain all three of the system’s angular-momentum vectors: how the companion spin axis, the stellar spin axis, and the orbit normal are inclined relative to our line of sight. To accomplish this, we measure projected rotation rates (v sin i) for both the star and the companion using new near-infrared high-resolution spectra with NIRSPEC at Keck Observatory. We combine these with a new stellar photometric rotation period from TESS and a published companion rotation period from Hubble Space Telescope to obtain spin-axis inclinations for both objects. We also fitted multiple epochs of astrometry, including a new observation with NIRC2/Keck, to measure 2M0122b’s orbital inclination. The three line-of-sight inclinations place limits on the true de-projected companion obliquity and stellar obliquity. We find that while the stellar obliquity marginally prefers alignment, the companion obliquity tentatively favors misalignment. We evaluate possible origin scenarios. While collisions, secular spin–orbit resonances, and Kozai–Lidov oscillations are unlikely, formation by gravitational instability in a gravito-turbulent disk—the scenario favored for brown dwarf companions to stars—appears promising.