用于ESPRESSO数据简化软件的基于模型的自动大地校正。径向速度计算的模型描述及应用
Automatic model-based telluric correction for the ESPRESSO data reduction software. Model description and application to radial velocity computation
摘要：
地面高分辨率摄谱仪是天体物理学若干领域的关键仪器。不幸的是，观测到的光谱被地球大气污染了。虽然在系外行星大气研究中存在不同的技术来校正大地线，但在径向速度（RV）研究中，吸收深度>2%的大地线通常被掩盖，这对微弱目标和M矮星造成了问题，因为它们的RV含量大部分存在于大地污染很重要的地方。我们提出了一个简单的大地模型嵌入在ESTERO DRS。目标是提供无大地光谱，使RV测量，包括大地线下降的光谱范围。该模式是一个逐线辐射转移代码，假设一个单一的大气层。我们使用天空条件和来自HITRAN的线的物理特性来创建大地光谱。选定的大地线的子集被用来通过Levenberg-Marquardt最小化算法稳健地拟合频谱。当应用到恒星光谱从A0到M5型的恒星，最强的H2O线的残差是低于2%的所有光谱型，除了M矮星，这是在伪连续。然后，我们确定的RV从碲校正ESTERO光谱的鲸鱼座τ和Proxima。我们创建了无碲掩模，并将获得的RV与DRS RV进行了比较。在鲸鱼座Tau的情况下，我们发现，微大地电磁线引入系统高达58厘米/秒的振幅和一年的周期。对于Proxima，在较红波长处的光谱内容的增益相当于光子噪声的25%的增益。这导致对Proxima d的半振幅和偏心率的更好约束。我们展示了我们的模型可以应用于其他分子，从而应用于其他光谱仪（如NIRPS）观察到的其他波长区域。
英文摘要：
Ground-based high-resolution spectrographs are key instruments for several astrophysical domains. Unfortunately, the observed spectra are contaminated by the Earth's atmosphere. While different techniques exist to correct for telluric lines in exoplanet atmospheric studies, in radial velocity (RV) studies, telluric lines with an absorption depth of >2% are generally masked, which poses a problem for faint targets and M dwarfs as most of their RV content is present where telluric contamination is important. We propose a simple telluric model to be embedded in the ESPRESSO DRS. The goal is to provide telluric-free spectra and enable RV measurements, including spectral ranges where telluric lines fall. The model is a line-by-line radiative transfer code that assumes a single atmospheric layer. We use the sky conditions and the physical properties of the lines from HITRAN to create the telluric spectrum. A subset of selected telluric lines is used to robustly fit the spectrum through a Levenberg-Marquardt minimization algorithm. When applied to stellar spectra from A0- to M5-type stars, the residuals of the strongest H2O lines are below 2% for all spectral types, with the exception of M dwarfs, which are within the pseudo-continuum. We then determined the RVs from the telluric-corrected ESPRESSO spectra of Tau Ceti and Proxima. We created telluric-free masks and compared the obtained RVs with the DRS RVs. In the case of Tau Ceti, we identified that micro-telluric lines introduce systematics up to an amplitude of 58 cm/s and with a period of one year. For Proxima, the gain in spectral content at redder wavelengths is equivalent to a gain of 25% in photon noise. This leads to better constraints on the semi-amplitude and eccentricity of Proxima d. We showcase that our model can be applied to other molecules, and thus to other wavelength regions observed by other spectrographs, such as NIRPS.
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