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CATEGORIES:Exoplanet Seminars
SUMMARY:Understanding and modelling activity-induced disto
 rtions in the absorption lines of Sun-like stars -
  Baptiste Klein (Oxford)
DTSTART;TZID=Europe/London:20230502T130000
DTEND;TZID=Europe/London:20230502T140000
UID:TALK200128AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/200128
DESCRIPTION:Stellar magnetic activity induces both distortions
  and Doppler-shifts in the absorption line profile
 s of Sun-like stars. Those produce apparent radial
  velocity (RV) signals which greatly hamper the se
 arch for potentially-habitable\, Earth-like planet
 s. With the advent of extreme-precision spectrogra
 phs\, it becomes crucial to develop robust methods
  to correct for the activity contributions while p
 reserving signatures of planetary origin. In the l
 ast few years\, innovative methods to exploit the 
 wealth of information present in line profiles rat
 her than just radial velocity time-series have sho
 wn promising results.\n\nI propose to review diffe
 rent activity modelling strategies involving the u
 se of stellar cross-correlation functions (CCFs)\,
  at the interface between the spectrum and the rad
 ial velocity measurement. I will focus on two main
  types of techniques\, both applied to observation
 s of the Sun\, intensively monitored with the high
 -precision spectrograph HARPS-N. In the first stra
 tegy\, activity-induced line-shape variations are 
 separated from pure Doppler shifts using data-driv
 en processes. The extracted line-shape temporal va
 riations are then included in a multi-dimensional 
 Gaussian process\, allowing us to robustly recover
  RV signatures as low as 0.4 m/s for planets in th
 e Sun’s habitable zone. The second method uses an 
 alternative physically-driven approach based on Do
 ppler Imaging to simultaneously reconstruct the di
 stribution of active regions at the surface of the
  stars and search for planet signatures shifting t
 he line profiles. Using solar data\, I demonstrate
  that Doppler imaging\, initially designed for rap
 idly-rotating stars\, can not only be applied to S
 un-like stars\, but also give reliable results in 
 term of planet detection. I will discuss the advan
 tages and limitations of both activity mitigation 
 strategy\, and potential avenues to overcome them.
 \n\n
LOCATION:Ryle seminar room + ONLINE - Details to be sent by
  email
CONTACT:Dr Emily Sandford
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