Issue |
A&A
Volume 683, March 2024
|
|
---|---|---|
Article Number | A63 | |
Number of page(s) | 9 | |
Section | Planets and planetary systems | |
DOI | https://doi.org/10.1051/0004-6361/202348328 | |
Published online | 08 March 2024 |
The Rossiter-McLaughlin effect and exoplanet transits: A delicate association at medium and low spectral resolution
1
Observatoire Astronomique de l’Université de Genève,
Chemin Pegasi 51b,
1290
Versoix,
Switzerland
e-mail: yann.carteret@unige.ch
2
Univ. Grenoble Alpes, CNRS, IPAG,
38000
Grenoble,
France
Received:
19
October
2023
Accepted:
7
December
2023
The characterization of exoplanetary atmospheres via transit spectroscopy is based on the comparison between the stellar spectrum filtered through the atmosphere and the unadulterated spectrum from the occulted stellar region. The disk-integrated spectrum is often used as a proxy for the occulted spectrum, yet they differ along the transit chord depending on stellar type and rotational velocity. This is referred to as the Rossiter-McLaughlin (RM) effect, which is known to bias transmission spectra at high spectral resolution when calculated with the disk-integrated stellar spectrum. Recently, it was shown that the first claimed atmospheric signal from an exoplanet cannot arise from absorption in the core of the sodium doublet, because the features observed at high resolution are well reproduced by the RM effect. However, it remains unclear as to whether the detection made at medium spectral resolution with the HST arises from the smoothed RM signature or from the wings of the planetary absorption line. More generally, the impact of the RM effect at medium and low spectral resolution remains poorly explored. To address this question, we simulated realistic transmission spectra in a variety of systems using the EVaporating Exoplanets code. We find that the Rm effect should not bias broadband atmospheric features, such as hazes or molecular absorption, measured with the JWST/NIRSPEC (prism mode) at low resolution. However, absorption signatures from metastable helium or sodium measured at medium resolution with the JWST/NIRSPEC (G140H mode) or HST/STIS can be biased, especially for planets on misaligned orbits across fast rotators. In contrast, we show that the Na signature originally reported in HD 209458b, an aligned system, cannot be explained by the RM effect, supporting a planetary origin. Contamination by the RM effect should therefore be accounted for when interpreting high- and medium-resolution transmission spectra of exoplanets.
Key words: methods: numerical / techniques: spectroscopic / planets and satellites: atmospheres / planets and satellites: individual: HD 209458 b
© The Authors 2024
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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