Recalibrating the SOPHIE Spectroscopic Archive to Identify Mass-Losing Exoplanets

McCune, Calum Scott (2016). Recalibrating the SOPHIE Spectroscopic Archive to Identify Mass-Losing Exoplanets. MPhil thesis The Open University.



Recent investigations of the WASP-12 system led to the discovery of an extensive thick and stable circumstellar gas cloud within being fed by material from the evaporating hot Jupiter planet WASP-12b (Haswell et al., 2012) (Fossati et al., 2010b). This planetary material veils the disc of the star providing a unique opportunity to probe composition via transmission spectroscopy. This would not be possible except for in this extreme scenario of catastrophic planet disintegration. Prior investigation of this system reported the anomalously low value of logR'HK = -5.50 (Knutson et al. 2010), which parameterises the activity in the Ca II H & K resonance line cores. A basal value of logR'HK = -5.1 is expected even for inactive main sequence stars (Henry et al. 1996; Wright 2004). Any stars with values below this lower limit must either be evolved or hosting similar gas shrouds. So far only a few such cases of this phenomenon have been identified but more are expected to be found within existing spectral archives. The intention of this project was to construct a reliable software pipeline for reducing large numbers of high resolution stellar spectra from the SOPHIE Echelle spectrograph with the eventual aim of producing archival measurements of the stellar activity parameter logR'HK for many stars. Integral to this goal was developing means of reliably achieving a good background subtraction of Echelle CCD spectra, specifically in the regions of the Ca II resonance lines, vital to the accurate measurement of logR'HK. The background subtraction software SKYBM was developed for this task and was then tested against existing background subtraction methods offered by the Echelle data reduction package ECHOMOP. SKYBM was found to provide the most accurate subtraction of all methods considered. This SKYBM software is therefore deemed appropriate for future work calibrating archival stellar spectra in terms of logR'HK to aid in the search for stars hosting mass losing planets.

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