Black Mirror: Detecting the Elusive Reflected Light Signal of 51 Pegasi b Using High Resolution Spectroscopy

The detection of the stellar light reflected by an exoplanet can provide a wealth of insight into that planet's atmosphere, internal heat and fundamental structure.   Unfortunately such a signal is challenging to isolate, and the reflected light has only previously been detected a couple of times in the optical regime. Highly-resolved spectral data, however, reveal a finely spaced forest of molecular lines. The reflected spectrum from an orbiting exoplanet is far more significantly Doppler shifted than that of its relatively stationary parent star. At high resolution, the spectral lines are deep and sharp enough that the Doppler shifted spectrum reflected from an exoplanet can be disentangled from the stellar spectrum.  Thus high resolution spectroscopy offers the possibility of extracting the elusive stellar reflection - and insights into the composition and structure of the exoplanet itself.

There is a necessity to perfect robust methods for characterising planetary atmospheres, including composition, structure and dynamics. Happily, when a star's reflection is captured from a planetary mirror, that planet's signature will be written into the light. I am using high-resolution data from HARPS-N of 51 Pegasi b - the first exoplanet and hot Jupiter ever discovered orbiting a Sun-like star. 51 Peg does not transit, therefore this high resolution method offers a new means of detecting the planet's signal and learning about its atmosphere. By cross correlating my data with models I can test the presence of a planetary signal to very high significance - drawing this planetary mirror out of the darkness.

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