Selective principal component extraction and reconstruction: a novel method for ground based exoplanet spectroscopy

Abstract

Context. Infrared spectroscopy of primary and secondary eclipse events probes the composition of exoplanet atmospheres and, using space telescopes, has detected H 2 O, CH 4 and CO 2 in three hot Jupiters. However, the available data from space telescopes has limited spectral resolution and does not cover the 2.4−5.2 μm spectral region. While large ground based telescopes have the potential to obtain molecular-abundance-grade spectra for many exoplanets, realizing this potential requires retrieving the astrophysical signal in the presence of large Earth-atmospheric and instrument systematic errors. Aims. Here we report a wavelet-assisted, selective principal component extraction method for ground based retrieval of the dayside spectrum of HD 189733b from data containing systematic errors. Methods. The method uses singular value decomposition and extracts those critical points of the Rayleigh quotient which correspond to the planet induced signal. The method does not require prior knowledge of the planet spectrum or the physical mechanisms causing systematic errors. Results. The spectrum obtained with our method is in excellent agreement with space based measurements made with HST and Spitzer and confirms the recent ground based measurements including the strong ∼3.3 μm emission.

NICMOS spectroscopy of HD 189733b

“…An ideal test of the Hubble/NICMOS results would be confirming observations with a different instrument. Recently reported, groundbased, near-IR emission spectra of HD 189733b Thatte et al 2010) are consistent with the previous Hubble/NICMOS measurements (Swain et al 2009a); this detection of the same spectral shape by two completely different instruments, with two completely different sets of systematics, is a strong indication that both instruments are measuring the exoplanet emission spectrum.…”

“…From this initial result, molecular spectroscopy of exoplanet atmospheres has grown rapidly, using Spitzer (Grillmair et al 2008), Hubble (Swain et al 2009a(Swain et al , 2009b, and ground-based measurements Thatte et al 2010;Snellen et al 2010). The alkali element sodium has also been detected in exoplanet atmospheres using Hubble, (Charbonneau et al 2002) and ground-based measurements have also been made (Redfield et al 2008;Snellen et al 2008).…”

Data analysis pipeline for EChO end-to-end simulations

“…These systematics tend to be due to array wide fluctuations of quantum efficiencies, insufficient flatfielding, slit-loss effects and pointing jitter. These complex non-Gaussian signals have shown to be important effects in real instruments [14,[27][28][29]. EChOSim implements inter and intra-pixel variations and non-Gaussian pointing jitter noise.…”

Of “Cocktail Parties” and Exoplanets

“…1901;Manly 1994;Jolliffe 2002;Press et al 2007). An application of PCA to exoplanetary light-curve de-trending is given by Thatte et al (2010). 2.…”

“…Hence, it is important to work toward an alternative route to quantify or remove systematic noise using non-parametric models that work as independent confirmations of existing results. Carter & Winn (2009), Thatte et al (2010), Gibson et al (2011b), and Waldmann et al (2012) have progressed toward non-parametric noise models and signal separation using wavelets, principal component, Gaussian processes and Fourier-based analysis.…”