Search

Stellar activity poses a severe limitation to the search and characterisation of small exoplanets with the radial velocity method. This is particularly important for M dwarfs, as they are crucial targets for both ground-based instruments (e.g., SPIRou, NIRPS, CRIRES) as well as space-based missions (e.g., JWST, ARIEL), but can manifest high activity levels over long time-scales. Efficient activity filtering techniques are therefore necessary to disentangle genuine planetary signatures and improve the detectability. In this context, and knowing from previous studies that different spectral lines are affected differently by magnetic activity, we developed a new mitigating technique based on a randomised selection of lines to use in Least-Square Deconvolution (LSD). We benchmarked the analysis on optical spectropolarimetric time series of the active M dwarf EV Lac collected with ESPaDOnS at CHFT, obtaining a reduction of the radial velocity dispersion by at least 50-60%. A similar and consistent improvement was also found when targeting stars of analogous (AD Leo) and lower (DS Leo) activity levels. Finally, we injected synthetic planets with semi-amplitudes between 60 and 120 m/s (i.e. 0.3-0.6 MJup) in our data sets containing moderate (20 m/s) and high (200 m/s) activity levels and we retrieved reasonably unaltered planetary signals, indicating that our technique does not suppress these signals substantially.

Stellar activity hinders the detection of small exoplanets with the radial velocity (RV) method, because it introduces spurious signals that can drown or mimic planetary signatures. It is therefore crucial to understand and filter out activity signals, especially in light of future small planet searches. We investigate ways to reduce activity jitter in RV time series using spectropolarimetric data sets in optical (ESPaDOnS@CHFT and NARVAL@TBL), and in near-infrared (nIR) with SPIRou@CHFT. We employ two approaches: 1) perform a chromatic study of typical stellar activity proxies, and 2) study a parametric selection of spectral lines to build a mask for Least-Square Deconvolution. The study is performed for EV Lac and AD Leo, two very active M dwarfs., {"references":["Queloz et al. 2001, A&A, 379, 279-287","Huelamo et al. 2008, A&A, 2, L9-L13","Donati et al. 1997, MNRAS, 291, 658","Boisse et al. 2009, A&A, 495, 959-966","Donati et al. 2016, Nature, 7609, 662-666","Hebrard et al. 2016, MNRAS, 461, 1465-1497","Haywood et al. 2014, MNRAS, 443, 2517-2531","Zechmeister & Kürster 2009, A&A, 496, 577-584"]}