Imaging & Spectroscopy

The ANTARESS workflow I. Optimal Extraction Of Spatially Resolved Stellar Spectra With High-resolution Transit Spectroscopy

By Keith Cowing
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astro-ph.EP
July 30, 2024
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The ANTARESS workflow I. Optimal Extraction Of Spatially Resolved Stellar Spectra With High-resolution Transit Spectroscopy
Mock ESPRESSO-like time series in the sodium D2 line, for HD 209458b (Rp = 1.36 RJ ; P = 3.5 d) and a mock companion (Rp = 2 RJ ; P = 7 d) transiting simultaneously HD 209458 (1.16 R@) with v sin i‹ = 15 km s´1 . The transit configuration is illustrated in Fig. 2. Orbital phases are relative to the outer planet. Dotted and dashed lines show the contacts of the inner and outer planets, respectively. Top left: In-transit disk-integrated profile distorted by the occultation of the two planets. Bottom left: Double-transit light curve. We note that photometric light curves are typically not an observable from ground-based spectroscopic datasets. Top right: RV derived from a Gaussian fit to the disk-integrated profile series (similar to the output of most spectrographs DRS), blending the well-known RM anomalies from the larger planet on a highly misaligned orbit („flat deviation) and from the smaller planet on its aligned orbit (S-shaped deviation). The solid blue line show the mock Keplerian stellar reflex motion. Bottom right: 2D map of intrinsic profiles (see Sect. 6.5), showing the tracks of local stellar lines occulted by the planets along their respective transit cores. — astro-ph.EP

High-resolution spectrographs open a detailed window onto the atmospheres of stars and planets. As the number of systems observed with different instruments grows, it is crucial to develop a standard in analyzing spectral time series of exoplanet transits and occultations, for the benefit of reproducibility.

Here, we introduce the ANTARESS workflow, a set of methods aimed at processing high-resolution spectroscopy datasets in a robust way and extracting accurate exoplanetary and stellar spectra. While a fast preliminary analysis can be run on order-merged 1D spectra and cross-correlation functions (CCFs), the workflow was optimally designed for extracted 2D echelle spectra to remain close to the original detector counts, limit the spectral resampling, and propagate the correlated noise.

Input data from multiple instruments and epochs were corrected for relevant environmental and instrumental effects, processed homogeneously, and analyzed independently or jointly. In this first paper, we show how planet-occulted stellar spectra extracted along the transit chord and cleaned from planetary contamination provide a direct comparison with theoretical stellar models and enable a spectral and spatial mapping of the photosphere.

We illustrate this application of the workflow to archival ESPRESSO data, using the Rossiter-McLaughlin effect Revolutions (RMR) technique to confirm the spin-orbit alignment of HD 209458 b and unveil biases in WASP-76 b’s published orbital architecture. Because the workflow is modular and its concepts are general, it can support new methods and be extended to additional spectrographs to find a range of applications beyond the proposed scope.

In a companion paper, we will present how planet-occulted spectra can be processed further to extract and analyze planetary spectra decontaminated from the star, providing clean and direct measurements of atmospheric properties.

V. Bourrier, J.-B. Delisle, C. Lovis, H. M. Cegla, M. Cretignier, R. Allart, K. Al Moulla, S. Tavella, O. Attia, D. Mounzer, V. Vaulato, M. Steiner, T. Vrignaud, S. Mercier, X. Dumusque, D. Ehrenreich, J. V. Seidel, A. Wyttenbach, W. Dethier, F. Pepe

Comments: 30 pages and 30 figures (plus Appendix). Accepted for publication in A&A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2407.19012 [astro-ph.EP] (or arXiv:2407.19012v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2407.19012
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Submission history
From: Vincent Bourrier Dr
[v1] Fri, 26 Jul 2024 18:00:07 UTC (16,204 KB)
https://arxiv.org/abs/2407.19012
Astrobiology,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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