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arXiv 2109.11235astro-ph.EPastro-ph.SR
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HAT-P-12 b透射光谱中恒星污染的证据

Evidence for stellar contamination in the transmission spectra of HAT-P-12b

C. Jiang, G. Chen, E. Palle, F. Murgas, H. Parviainen, F. Yan, Y. Ma

摘要:

透射光谱表征了过境深度的波长依赖性,揭示了行星终结者区域的大气吸收特征。在这种情况下,先前研究中报道的HAT-P-12 b的不同光学透射光谱表现出不一致的大气特征(例如,瑞利散射、碱吸收)。我们的目标是利用加那利大望远镜(GTC)的两次过境光谱观测来了解HAT-P-12 b的大气,并寻找恒星活动污染透射光谱的证据,这可能是差异背后的原因。我们使用高斯过程来解释过境光变曲线中的系统噪声,并使用嵌套采样进行贝叶斯推断。我们进行了联合大气反演使用GTC OSIRIS获得的两个透射光谱,以及以前发表的结果,再加上不同的观测恒星污染校正。反演的大气模式没有显示出碱吸收特征,但显示出初步的分子吸收特征,包括$\rm H_2O$,$\rm CH_4$和$\rm NH_3$。组合的附加公共数据分析的联合检索检索到类似的结果,但具有更高的金属丰度。基于贝叶斯模型比较,HAT-P-12 b透射谱的差异可以用不同水平的未掩星斑和光斑的影响来解释。此外,我们没有从联合分析中找到多云或朦胧大气的有力证据,这与先前基于哈勃太空望远镜观测的研究不一致。

英文摘要:

Transmission spectroscopy characterizes the wavelength dependence of transit depth, revealing atmospheric absorption features in planetary terminator regions. In this context, different optical transmission spectra of HAT-P-12b reported in previous studies exhibited discrepant atmospheric features (e.g., Rayleigh scattering, alkali absorption). We aim to understand the atmosphere of HAT-P-12b using two transit spectroscopic observations by the Gran Telescopio CANARIAS (GTC), and to search for evidence of stellar activity contaminating the transmission spectra, which might be the reason behind the discrepancies. We used Gaussian processes to account for systematic noise in the transit light curves and used nested sampling for Bayesian inferences. We performed joint atmospheric retrievals using the two transmission spectra obtained by GTC OSIRIS, as well as previously published results, coupled with stellar contamination corrections for different observations. The retrieved atmospheric model exhibits no alkali absorption signatures, but shows tentative molecular absorption features including $\rm H_2O$, $\rm CH_4$ and $\rm NH_3$. The joint retrieval of the combined additional public data analysis retrieves similar results, but with a higher metallicity. Based on Bayesian model comparison, the discrepancies of the transmission spectra of HAT-P-12b can be explained by the effect of different levels of unocculted stellar spots and faculae. In addition, we did not find strong evidence for a cloudy or hazy atmosphere from the joint analysis, which is inconsistent with prior studies based on the observations of Hubble Space Telescope.

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