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SUMMARY:Understanding and modelling activity-induced distortions in the ab
 sorption lines of Sun-like stars - Baptiste Klein (Oxford)
DTSTART:20230502T120000Z
DTEND:20230502T130000Z
UID:TALK200128@talks.cam.ac.uk
CONTACT:Dr Emily Sandford
DESCRIPTION:Stellar magnetic activity induces both distortions and Doppler
 -shifts in the absorption line profiles of Sun-like stars. Those produce a
 pparent radial velocity (RV) signals which greatly hamper the search for p
 otentially-habitable\, Earth-like planets. With the advent of extreme-prec
 ision spectrographs\, it becomes crucial to develop robust methods to corr
 ect for the activity contributions while preserving signatures of planetar
 y origin. In the last few years\, innovative methods to exploit the wealth
  of information present in line profiles rather than just radial velocity 
 time-series have shown promising results.\n\nI propose to review different
  activity modelling strategies involving the use of stellar cross-correlat
 ion functions (CCFs)\, at the interface between the spectrum and the radia
 l velocity measurement. I will focus on two main types of techniques\, bot
 h applied to observations of the Sun\, intensively monitored with the high
 -precision spectrograph HARPS-N. In the first strategy\, activity-induced 
 line-shape variations are separated from pure Doppler shifts using data-dr
 iven processes. The extracted line-shape temporal variations are then incl
 uded in a multi-dimensional Gaussian process\, allowing us to robustly rec
 over RV signatures as low as 0.4 m/s for planets in the Sun’s habitable 
 zone. The second method uses an alternative physically-driven approach bas
 ed on Doppler Imaging to simultaneously reconstruct the distribution of ac
 tive regions at the surface of the stars and search for planet signatures 
 shifting the line profiles. Using solar data\, I demonstrate that Doppler 
 imaging\, initially designed for rapidly-rotating stars\, can not only be 
 applied to Sun-like stars\, but also give reliable results in term of plan
 et detection. I will discuss the advantages and limitations of both activi
 ty mitigation strategy\, and potential avenues to overcome them.\n\n
LOCATION:Ryle seminar room + ONLINE - Details to be sent by email
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