TRANSIT AND ECLIPSE ANALYSES OF THE EXOPLANET HD 149026b USING BLISS MAPPING

Abstract

The dayside of HD 149026b is near the edge of detectability by the Spitzer Space Telescope. We report on eleven secondary-eclipse events at 3.6, 4.5, 3 × 5.8, 4 × 8.0, and 2 × 16 µm plus three primary-transit events at 8.0 µm. The eclipse depths from jointly-fit models at each wavelength are 0.040 ± 0.003% at 3.6 µm, 0.034 ± 0.006% at 4.5 µm, 0.044 ± 0.010% at 5.8 µm, 0.052 ± 0.006% at 8.0 µm, and 0.085 ± 0.032% at 16 µm. Multiple observations at the longer wavelengths improved eclipse-depth signal-to-noise ratios by up to a factor of two and improved estimates of the planet-to-star radius ratio (R p /R ⋆ = 0.0518 ± 0.0006). We also identify no significant deviations from a circular orbit and, using this model, report an improved period of 2.8758916 ± 0.0000014 days. Chemical-equilibrium models find no indication of a temperature inversion in the dayside atmosphere of HD 149026b. Our best-fit model favors large amounts of CO and CO 2 , moderate heat redistribution ( f = 0.5), and a strongly enhanced metallicity. These analyses use BiLinearly-Interpolated Subpixel Sensitivity (BLISS) mapping, a new technique to model two position-dependent systematics (intrapixel variability and pixelation) by mapping the pixel surface at high resolution. BLISS mapping outperforms previous methods in both speed and goodness of fit. We also present an orthogonalization technique for linearly-correlated parameters that accelerates the convergence of Markov chains that employ the Metropolis random walk sampler. The electronic supplement contains light-curve files and supplementary figures.

The HARPS-N Rocky Planet Search

“…The third, optional, function was a polynomial of the logarithm of time + a slope to represent a sharp decrease of the detector response at the start of the AOR ("ramp" effect, Knutson et al 2008). To improve the quality of the modelling of the pixel phase effect, especially the fitting of its highest frequency components, we supplemented the x-and y-polynomial with the Bi-Linearly-Interpolated Sub-pixel Sensitivity (BLISS) mapping method (Stevenson et al 2012). The sampling of the positions in space was selected so that at least five measurements fall within the same subpixel.…”

“…Spitzer photometry divided by two different best-fit baseline models. The first (top) aims to remove position-and PSF effects, and consists of a 4th order polynomial of the PSF x-and y-centres and widths, supplemented with the BLISS mapping method (Stevenson et al 2012) to remove high-frequency position effects. The second baseline model (bottom) adds to the first a slope and a quadratic function of the logarithm of time to model the sharp decrease in the counts at the beginning of the run (negative ramp).…”

Variability in the super-Earth 55 Cnc e

“…In the present work, we use a modified implementation of the BLISS (BiLinearly-Interpolated Subpixel Sensitivity) method (Stevenson et al 2012).…”

A global analysis ofSpitzerand new HARPS data confirms the loneliness and metal-richness of GJ 436 b

“…For an improved modelling of the effect, Ballard et al (2010a) and Stevenson et al (2012a) demonstrated the efficiency of building a "pixel map" to characterise the intra-pixel variability on a fine grid. Here we combine the bi-linearly-interpolated sub-pixel sensitivity (BLISS) mapping method presented by Stevenson et al (2012a) with the position/FWHM polynomial models. The BLISS mapping is performed at every step of the chain after the modelling of the polynomial models.…”