University of Cambridge > Talks.cam > Institute of Astronomy Seminars > Robustness of Molecular Detections Using High-Resolution Transmission Spectroscopy

Robustness of Molecular Detections Using High-Resolution Transmission Spectroscopy

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In recent years, high-resolution transmission spectroscopy has emerged as one of the most successful techniques for detecting chemicals in transiting exoplanetary atmospheres. Despite many molecular detections to date, concerns have been raised about robustness when removing telluric and stellar features from the observed spectra, a step known as detrending. A robust detrending method has yet to be agreed upon, leaving previous detections inconsistent and sometimes irreproducible. We examine how overfitting detrending parameters can falsely amplify detection significances, and propose a robust methodology to select these parameters without introducing bias. To do this, we use CARMENES observations of the hot Jupiter HD189733b as a case study to investigate the robustness of different detrending optimisations. We find that selecting detrending parameters by optimising the difference between a signal-injected cross-correlation function and the observed cross-correlation function is robust against noise and spurious signals. On the other hand, optimising without this subtraction, as is often done, can induce spurious peaks and inflate detection significances. We reproduce previous detections with decreased significances reflecting more robust detrending. Our findings provide a robust framework for future homogeneous molecular surveys of exoplanetary atmospheres using high-resolution transmission spectroscopy.

This talk is part of the Institute of Astronomy Seminars series.

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