Abstract
Context. Stellar activity limits the radial velocity (RV) search and characterisation of exoplanets, as it introduces spurious noise (called jitter) in the data sets and prevents the correct retrieval of a planetary signal. This is key for M dwarfs, considering that they manifest high activity levels and are primary targets for present and future searches of habitable Earth-like planets. To perform precise RV measurements, multi-line numerical techniques like cross-correlation and least-squares deconvolution (LSD) are typically employed. Aims. Effective filtering of activity is crucial to achieving the sensitivity required for small planet detections. Here we analyse the impact of selecting different line lists for LSD on the dispersion in our RV data sets, to identify the line list that most effectively reduces the jitter. Methods. We employ optical spectropolarimetric observations of the active M dwarf EV Lac collected with ESPaDOnS and NARVAL, and study two line down-selection approaches: a parametric method based on line properties (depth, wavelength, magnetic sensitivity) and a randomised algorithm that samples the line combination space. We test the latter further to find the line list that singles out the activity signal from other sources of noise, and on AD Leo and DS Leo to examine its consistency at mitigating jitter for different activity levels. The analysis is complemented with planetary injection tests. Results. The parametric selection yields a RV RMS reduction of less than 10%, while the randomised selection yields a systematic improvement (>50%) regardless of the activity level of the star examined. Furthermore, if activity is the dominant source of noise, this approach allows the construction of lists containing mainly activity-sensitive lines, which could be used to enhance the rotational modulation of the resulting data sets and determine the stellar rotation period more robustly. Finally, the output line lists allow the recovery of a synthetic planet (0.3–0.6 MJup on a 10 d orbit) in the presence of both moderate (20 m s−1 semi-amplitude) and high (200 m s−1) activity levels, without substantially affecting the planet signal (between 60 and 120 m s−1).
Highlights
A key scientific objective of exoplanetary sciences is to find and characterise habitable Earth-like planets, scrutinise their atmosphere and search for potential biomarkers; it is the main driver for current space-based missions such as TESS and CHEOPS (Ricker et al 2015; Benz et al 2020), as well as for future ones like JWST, PLATO, and ARIEL (Gardner et al 2006; Rauer et al 2014; Tinetti et al 2018) and ground-based facilities like ESO ELT (Marconi et al 2021)
We have carried out a study of the effects of different line masks for least-squares deconvolution on the dispersion of radial velocity (RV) data sets, with the intent to build a mask that mitigates the effects of activity jitter
This is of particular importance for M dwarfs, given their notoriously high activity levels, and their key role in future small planet searches
Summary
A key scientific objective of exoplanetary sciences is to find and characterise habitable Earth-like planets, scrutinise their atmosphere and search for potential biomarkers; it is the main driver for current space-based missions such as TESS and CHEOPS (Ricker et al 2015; Benz et al 2020), as well as for future ones like JWST, PLATO, and ARIEL (Gardner et al 2006; Rauer et al 2014; Tinetti et al 2018) and ground-based facilities like ESO ELT (Marconi et al 2021). RV measurements are commonly performed with numerical techniques such as cross correlation (Baranne et al 1996; Pepe et al 2002), least-squares deconvolution (LSD, Donati et al 1997; Kochukhov et al 2010) and least-squares template matching (e.g., Anglada-Escudé & Butler 2012; Astudillo-Defru et al 2015; Zechmeister et al 2018) The latter technique gives precise results for M dwarfs, because it makes use of a master spectrum template with high signal-to-noise ratio (SNR) and with a richer RV content than a synthetic spectrum with a lower number of absorption lines.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
