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arXiv 2007.13510astro-ph.EP
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用FORS2进行地基透射光谱学:超热木星WASP-103 b的无特征光学透射光谱和H $_2$ O探测

Ground-Based Transmission Spectroscopy with FORS2: A featureless optical transmission spectrum and detection of H$_2$O for the ultra-hot Jupiter WASP-103b

J. Wilson, N. P. Gibson, N. Nikolov, S. Constantinou, N. Madhusudhan, J. Goyal, J. K. Barstow, A. L. Carter, E. J. W. de Mooij, B. Drummond, T. Mikal-Evans, C. … 展开作者

J. Wilson, N. P. Gibson, N. Nikolov, S. Constantinou, N. Madhusudhan, J. Goyal, J. K. Barstow, A. L. Carter, E. J. W. de Mooij, B. Drummond, T. Mikal-Evans, C. Helling, N. J. Mayne, D. K. Sing

摘要:

我们报告的高度辐射和超短周期热木星WASP-103 b覆盖的波长范围$\approx$ 400-600 nm的甚大望远镜上使用FORS 2仪器的地基透射光谱。光变曲线显示出显著的时间相关噪声,其主要在波长上是不变的,并且我们使用高斯过程对其进行建模。我们的透射光谱的精度得到改善,通过应用来自白光曲线的共模校正,达到典型的不确定性在过渡深度$\approx$ 2 × 10 $^{-4}$在15 nm的波长箱。经过混合伴星的通量污染校正后,我们的观测结果显示FORS 2观测的整个范围内都是一个无特征的光谱,我们无法确认先前使用Gemini/GMOS推断的Na吸收或使用宽带光变曲线观察到的强瑞利散射。我们使用Gemini/GMOS,HST/WFC 3和Spitzer观测的额外数据对全光红外透射光谱进行了贝叶斯大气反演,并在4.0 $σ$水平上恢复了H $_2$ O吸收的证据。然而,我们的观察不能完全排除Na的存在,在我们的检索中发现Na在2.0 $σ$。这可以部分地解释为片状/不均匀的云或薄雾阻尼了我们的FORS 2光谱中的任何吸收特征,但是固有的小尺度高度也使得从地面探测该特征具有挑战性。尽管如此,我们的研究结果表明,地面观测调查系外行星大气的持续潜力,并强调需要应用一致和强大的统计技术,低分辨率光谱仪器系统学的存在。

英文摘要:

We report ground-based transmission spectroscopy of the highly irradiated and ultra-short period hot-Jupiter WASP-103b covering the wavelength range $\approx$ 400-600 nm using the FORS2 instrument on the Very Large Telescope. The light curves show significant time-correlated noise which is mainly invariant in wavelength and which we model using a Gaussian process. The precision of our transmission spectrum is improved by applying a common-mode correction derived from the white light curve, reaching typical uncertainties in transit depth of $\approx$ 2x10$^{-4}$ in wavelength bins of 15 nm. After correction for flux contamination from a blended companion star, our observations reveal a featureless spectrum across the full range of the FORS2 observations and we are unable to confirm the Na absorption previously inferred using Gemini/GMOS or the strong Rayleigh scattering observed using broad-band light curves. We performed a Bayesian atmospheric retrieval on the full optical-infrared transmission spectrum using the additional data from Gemini/GMOS, HST/WFC3 and Spitzer observations and recover evidence for H$_2$O absorption at the 4.0$σ$ level. However, our observations are not able to completely rule out the presence of Na, which is found at 2.0$σ$ in our retrievals. This may in part be explained by patchy/inhomogeneous clouds or hazes damping any absorption features in our FORS2 spectrum, but an inherently small scale height also makes this feature challenging to probe from the ground. Our results nonetheless demonstrate the continuing potential of ground-based observations for investigating exoplanet atmospheres and emphasise the need for the application of consistent and robust statistical techniques to low-resolution spectra in the presence of instrumental systematics.

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