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arXiv 2302.04574astro-ph.EPastro-ph.SR
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使用优化检索框架修正恒星活动对系外行星透射光谱的影响

Correcting Exoplanet Transmission Spectra for Stellar Activity with an Optimised Retrieval Framework

Alexandra Thompson, Alfredo Biagini, Gianluca Cracchiolo, Antonino Petralia, Quentin Changeat, Arianna Saba, Giuseppe Morello, Mario Morvan, Giuseppina Micela, Giovanna Tinetti

AI总结:

本研究使用StARPA和ASteRA两种恒星模型及TauREx3框架,基于27个合成光谱评估恒星活动对系外行星透射光谱检索的偏差,发现包含恒星活动参数可最小化偏差,ASteRA在中低活动下表现优异,但在高活动下因忽略黑子与临边昏暗效应的相互作用而存在微小残余偏差。

摘要:

主星上由光球层不均匀性(例如黑子和光斑)引起的色度污染,构成了系外行星透射光谱的一个显著噪声源。如果不修正这种污染,会在我们分析行星大气时引入显著偏差。我们利用两个复杂程度不同的恒星模型(StARPA和ASteRA),来探索在不同恒星活动程度下,恒星污染在检索中引入的偏差。我们使用检索框架TauREx3和由27个合成的受黑子污染的透射光谱组成的网格,来调查潜在偏差,并确定我们的恒星模型需要达到何种复杂程度,才能从透射光谱中准确提取行星参数。输入观测是使用更复杂的模型(StARPA)生成的,其中黑子纬度是一个额外的、可固定的参数。然后将该观测数据输入到一个包含简化恒星模型(ASteRA)的恒星-行星联合检索中。我们的结果证实,在所考虑的所有活动状态下,在检索中包含恒星活动参数可使偏差最小化。ASteRA在低至中等活动条件下表现非常出色,能以高精度检索出行星参数。对于最活跃的情况,其特征是更大、温度对比更高的黑子,由于ASteRA忽略了黑子与临边昏暗效应之间的相互作用,仍然存在一些微小的残余偏差。因此,我们发现对于中心黑子(0度)和靠近临边的黑子(60度),检索到的行星参数的误差比中间纬度(30度)的黑子更大。

英文摘要:

The chromatic contamination that arises from photospheric heterogeneities e.g. spots and faculae on the host star presents a significant noise source for exoplanet transmission spectra. If this contamination is not corrected for, it can introduce substantial bias in our analysis of the planetary atmosphere. We utilise two stellar models of differing complexity, StARPA and ASteRA, to explore the biases introduced by stellar contamination in retrieval under differing degrees of stellar activity. We use the retrieval framework TauREx3 and a grid of 27 synthetic, spot-contaminated transmission spectra to investigate potential biases and to determine how complex our stellar models must be in order to accurately extract the planetary parameters from transmission spectra. The input observation is generated using the more complex model (StARPA), in which the spot latitude is an additional, fixable parameter. This observation is then fed into a combined stellar-planetary retrieval which contains a simplified stellar model (ASteRA). Our results confirm that the inclusion of stellar activity parameters in retrieval minimises bias under all activity regimes considered. ASteRA performs very well under low to moderate activity conditions, retrieving the planetary parameters with a high degree of accuracy. For the most active cases, characterised by larger, higher temperature contrast spots, some minor residual bias remains due to ASteRA neglecting the interplay between the spot and the limb darkening effect. As a result of this, we find larger errors in retrieved planetary parameters for central spots (0 degrees) and those found close to the limb (60 degrees) than those at intermediate latitudes (30 degrees).

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