Selective Principal Component Extraction and Reconstruction: A Novel Method for Ground Based Exoplanet Spectroscopy

摘要

Context: Infrared spectroscopy of primary and secondary eclipse events probesthe composition of exoplanet atmospheres and, using space telescopes, hasdetected H2O, CH4 and CO2 in three hot Jupiters. However, the available datafrom space telescopes has limited spectral resolution and does not cover the2.4 - 5.2 micron spectral region. While large ground based telescopes have thepotential to obtain molecular-abundance-grade spectra for many exoplanets,realizing this potential requires retrieving the astrophysical signal in thepresence of large Earth-atmospheric and instrument systematic errors. Aims:Here we report a wavelet-assisted, selective principal component extractionmethod for ground based retrieval of the dayside spectrum of HD 189733b fromdata containing systematic errors. Methods: The method uses singular valuedecomposition and extracts those critical points of the Rayleigh quotient whichcorrespond to the planet induced signal. The method does not require priorknowledge of the planet spectrum or the physical mechanisms causing systematicerrors. Results: The spectrum obtained with our method is in excellentagreement with space based measurements made with HST and Spitzer (Swain et al.2009b; Charbonneau et al. 2008) and confirms the recent ground basedmeasurements (Swain et al. 2010) including the strong 3.3 micron emission.