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arXiv 2103.15124astro-ph.EPastro-ph.IM
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一种新的光谱相位曲线研究方法:WASP-12 b的发射光谱与HST/WFC3正交观测

A new approach to spectroscopic phase curves: The emission spectrum of WASP-12b observed in quadrature with HST/WFC3

J. Arcangeli, J. -M. Désert, V. Parmentier, S. -M. Tsai, K. B. Stevenson

摘要:

我们分析发射光谱的WASP-12 b从部分相位曲线观察到三个时代的哈勃太空望远镜,涵盖日食,正交和过境,分别。由于1.1天周期的相位曲线在三个历元中只被部分覆盖,传统的提取行星通量和仪器系统误差的方法无法恢复二次日食的热辐射。为了分析该部分相位曲线,我们引入了一种新的方法,该方法校正了系统误差中与波长无关的分量。我们的新方法删除了消色差仪器和恒星的变化,并使用在日食测量恒星光谱,然后检索在每个阶段的波长相对行星光谱。我们能够提取的系外行星的发射光谱在正交以外的相位曲线的第一次,我们恢复WASP-12 b的正交光谱的添加剂常数。以类似的方式提取昼侧发射光谱,在这两种情况下,我们都能够估计亮度温度,尽管精度大大降低。我们估计的亮温从向阳面(Tday=3186+-677 K)和从正交光谱(Tquad=2124+-417 K),并结合它们来约束行星的能量预算。我们将我们提取的相对光谱与这个星球的全球环流模型进行比较,这通常被认为是一个很好的匹配。然而,我们确实看到了与我们的模型相比,在测量的昼侧光谱中光谱斜率更陡的初步证据。我们发现,我们不能通过增加我们的模型中的光学不透明度来匹配这种增加的斜率。我们还发现,这种光谱斜率是不太可能被解释的非平衡态水丰度,因为水平流从阴面上的阳面迅速解离。

英文摘要:

We analyse emission spectra of WASP-12b from a partial phase curve observed over three epochs with the Hubble Space Telescope, covering eclipse, quadrature, and transit, respectively. As the 1.1-day period phase curve was only partially covered over three epochs, traditional methods to extract the planet flux and instrument systematic errors cannot recover the thermal emission away from the secondary eclipse. To analyse this partial phase curve, we introduce a new method, which corrects for the wavelength-independent component of the systematic errors. Our new method removes the achromatic instrument and stellar variability, and uses the measured stellar spectrum in eclipse to then retrieve a relative planetary spectrum in wavelength at each phase. We are able to extract the emission spectrum of an exoplanet at quadrature outside of a phase curve for the first time; we recover the quadrature spectrum of WASP-12b up to an additive constant. The dayside emission spectrum is extracted in a similar manner, and in both cases we are able to estimate the brightness temperature, albeit at a greatly reduced precision. We estimate the brightness temperature from the dayside (Tday=3186+-677 K) and from the quadrature spectrum (Tquad=2124+-417 K) and combine them to constrain the energy budget of the planet. We compare our extracted relative spectra to global circulation models of this planet, which are generally found to be a good match. However, we do see tentative evidence of a steeper spectral slope in the measured dayside spectrum compared to our models. We find that we cannot match this increased slope by increasing optical opacities in our models. We also find that this spectral slope is unlikely to be explained by a non-equilibrium water abundance, as water advected from the nightside is quickly dissociated on the dayside.

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