title: Search for extrasolar planets around young stars in the presence of stellar activity
creator: Mohler-Fischer, Maren
subject: 520
subject: 520 Astronomy and allied sciences
description: Planets form in circumstellar disks around newly born stars. The timescales of planet formation and migration remain poorly constrained and are a matter of ongoing debate.  The disk dispersal timescale, which sets a limit to the duration of planet formation, was derived from infrared surveys to be less than 10Myr. In order to test the predicted planet formation time scales described in current theories, it is important to find planets in the age range of 1 to 100Myrs. In the same manner, non-detections can help to understand the current theories. However, the number of discoveries is still very small due to the challenging task to analyze RV signals contaminated by the high stellar activity.  Within this thesis, I performed a systematic radial velocity (RV) search for planets around 21 young targets with ages between ~3 and ~400Myr and spectral types between F6 and M0. In order to account for the strong stellar activity, I analyzed the stellar spectra in terms of a variety of activity indicators, analyzing both single spectral lines and the RV cross-correlation function. For three targets, a strong radial velocity signal could be identified, which was not induced by measurement sampling. Due to the analysis of available photometric data and activity indicators, it was possible to exhibit stellar activity patterns such as cool stellar spots as origin of the signal. The simulation with a spot program allowed to reconstruct possible spot scenarios that could have caused the detected RV variability.  The challenge of the conformation of a transit planet with follow-up observations in presence of stellar activity is shown in the discussion of HATS-2b, a transiting extrasolar planet orbiting a K-type star showing starspot activity.  Furthermore, the discussion of a possible companion around the young eruptive star EX Lupi is part of this thesis. The detailed RV and activity analyses show the challenging task to disentangle RV signals caused by a possible companions and by stellar activity.  Although no planet could be identified in the RV search around 21 young stars, it can in summary be stated that the detailed analyses in this thesis allow to put constraints on further RV surveys looking for exoplanets around young stars. This includes not only the sample size and target selection but also the observations and data analysis methods.
date: 2013
type: Dissertation
type: info:eu-repo/semantics/doctoralThesis
type: NonPeerReviewed
format: application/pdf
identifier: https://archiv.ub.uni-heidelberg.de/volltextserverhttps://archiv.ub.uni-heidelberg.de/volltextserver/15633/1/PhD_M_Mohler-Fischer_2013.pdf
identifier: DOI:10.11588/heidok.00015633
identifier: urn:nbn:de:bsz:16-heidok-156338
identifier:   Mohler-Fischer, Maren  (2013) Search for extrasolar planets around young stars in the presence of stellar activity.  [Dissertation]     
relation: https://archiv.ub.uni-heidelberg.de/volltextserver/15633/
rights: info:eu-repo/semantics/openAccess
rights: http://archiv.ub.uni-heidelberg.de/volltextserver/help/license_urhg.html
language: eng