Observation and Modeling of Extrasolar Planets

Carter, Andrew James (2012). Observation and Modeling of Extrasolar Planets. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000ee26


The field of exoplanet research has currently yielded the discovery of 552 planets. This figure includes 132 transiting planets which can be studied in greater detail and have formed the cornerstone of research to characterise the exoplanet population. In particular, such studies seek to analyse the planetary atmospheres, but research has thus far yielded more questions than answers.

Exoplanetary atmospheric studies have typically focussed on one planet apiece - complicating any comparative analysis as every result employs different methods and instruments. For a comprehensive, comparative study, a robust and reliable means of reducing and analysing such observations is required, along with a body of data from a single instrument.

One such instrument is the Bubble Space Telescope (BST) whose NICMOS (Near Infrared Camera and Multi-Object Spectrometer) instrument has observed the transits of nine extrasolar planets across multiple wavelengths in the near-infrared. A robust pipeline has been developed to reduce all such observations using the fame techniques.

This pipeline reduces grism images of an exoplanet host star across a transit event. These exposures are checked for bad pixels, flat fielded and background-subtracted before robust extraction of a transit light curve. This light curve is then detrended to remove systematic noise by application of a new technique developed in this study. Following detrending, the light curve is modelled using a be- spoke MCMC (Markov-Chain Monte-Carlo) algorithm to determine the planetary parameters. A continuum of wavelength-dependent transit light curves is also extracted, detrended and modelled to de- termine the variation in transit depth with wavelength; and .hereby infer the transmission spectrum of the planet's atmosphere.

The finished pipeline has been applied to three sets of HST NIC- MOS observations covering the transits of WASP-2b, HD189733b and GJ436b. For each data set, a new set of planetary parameters has been derived and for WASP-2b and HD189733b an atmospheric transmission spectrum extracted. Both spectra show signs of atmospheric haze and molecular absorption, but also evidence of residual systematic noise, complicating analysis.

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