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arXiv 2004.14812astro-ph.EPastro-ph.SR
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由恒星快速自转和自旋-轨道错位引起的KELT-9 b的不对称TESS Transit

KELT-9 b's Asymmetric TESS Transit Caused by Rapid Stellar Rotation and Spin-Orbit Misalignment

John P. Ahlers, Marshall C. Johnson, Keivan G Stassun, Knicole D. Colon, Jason W. Barnes, Daniel J. Stevens, Thomas Beatty, B. Scott Gaudi, Karen A. Collins, Jo… 展开作者

John P. Ahlers, Marshall C. Johnson, Keivan G Stassun, Knicole D. Colon, Jason W. Barnes, Daniel J. Stevens, Thomas Beatty, B. Scott Gaudi, Karen A. Collins, Joseph Rodriguez, George Ricker, Roland Vanderspek, David Latham, Sara Seager, Joshua Winn, Jon M. Jenkins, Douglas A. Caldwell, Robert F. Goeke, Hugh P. Osborn, Martin Paegert, Pam Rowden, Peter Tenenbaum

摘要:

KELT-9 b是一颗超热的木星,在极地轨道上经过一颗快速旋转的扁圆早A型恒星。我们模拟快速恒星旋转对KELT-9 b的凌日光变曲线的影响,使用凌日系外行星勘测卫星(\tess)的测光来限制行星的真实自旋轨道角,并探索KELT-9 b如何受到恒星重力变暗的影响。我们约束宿主星的赤道半径是其极地半径的$1.089\pm0.017$倍,其局部表面亮度在其热极和冷赤道之间变化$\sim38$ \%。我们建立了恒星扁率和表面亮度梯度的模型,发现它导致凌日光变曲线在最小光时附近缺乏通常的对称性。我们利用光变曲线的不对称性来限制KELT-9 b的真实自旋轨道角(${87^\circ}^{+10^\circ}_{-11^\circ}$),与\citet{gaudi2017giant}一致,KELT-9 b处于近极轨道。我们还应用重力暗化校正的光谱能量分布模型从\citet{gaudi2017giant},并发现会计快速旋转提供了一个更好的适合可用的光谱,并产生一个更可靠的估计恒星的极地有效温度。

英文摘要:

KELT-9 b is an ultra hot Jupiter transiting a rapidly rotating, oblate early-A-type star in a polar orbit. We model the effect of rapid stellar rotation on KELT-9 b's transit light curve using photometry from the Transiting Exoplanet Survey Satellite (\tess) to constrain the planet's true spin-orbit angle and to explore how KELT-9 b may be influenced by stellar gravity darkening. We constrain the host star's equatorial radius to be $1.089\pm0.017$ times as large as its polar radius and its local surface brightness to vary by $\sim38$\% between its hot poles and cooler equator. We model the stellar oblateness and surface brightness gradient and find that it causes the transit light curve to lack the usual symmetry around the time of minimum light. We take advantage of the light curve asymmetry to constrain KELT-9 b's true spin orbit angle (${87^\circ}^{+10^\circ}_{-11^\circ}$), agreeing with \citet{gaudi2017giant} that KELT-9 b is in a nearly polar orbit. We also apply a gravity darkening correction to the spectral energy distribution model from \citet{gaudi2017giant} and find that accounting for rapid rotation gives a better fit to available spectroscopy and yields a more reliable estimate for the star's polar effective temperature.

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