The climate of HD 189733b from fourteen transits and eclipses measured by Spitzer

• Published in: arXiv.org
• Main Authors: Agol, E, Cowan, N B, Knutson, H A, Deming, D, Steffen, J H, Henry, G W, Charbonneau, D
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 26.07.2010
• Subjects: Astronomical models; Atmospheric models; Darkening; Eclipses; Egress; Exponential functions; Extrasolar planets; Mars; Night; Orbital resonances (celestial mechanics); Photosphere; Physics - Earth and Planetary Astrophysics; Planetary atmospheres; Stellar atmospheres; Surface brightness; Time lag; Transit; Travel time
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1007.4378

We present observations of seven transits and seven eclipses of the transiting planet system HD 189733 taken with Spitzer IRAC at 8 microns. We use a new correction for the detector ramp variation with a double-exponential function. Our main findings are: (1) an upper limit on the variability of the day-side planet flux of 2.7% (68% confidence); (2) the most precise set of transit times measured for a transiting planet, with an average accuracy of 3 seconds; (3) a lack of transit-timing variations, excluding the presence of second planets in this system above 20% of the mass of Mars in low-order mean-motion resonance at 95% confidence; (4) a confirmation of the planet's phase variation, finding the night side is 64% as bright as the day side, as well as an upper limit on the night-side variability of 17% (68% confidence); (5) a better correction for stellar variability at 8 micron causing the phase function to peak 3.5 hrs before secondary eclipse, confirming that the advection and radiation timescales are comparable at the 8 micron photosphere; (6) variation in the depth of transit, which possibly implies variations in the surface brightness of the portion of the star occulted by the planet, posing a fundamental limit on non-simultaneous multi-wavelength transit absorption measurements of planet atmospheres; (7) a measurement of the infrared limb-darkening of the star, in agreement with stellar atmosphere models; (8) an offset in the times of secondary eclipse of 69 sec, which is mostly accounted for by a 31 sec light travel time delay and 33 sec delay due to the shift of ingress and egress by the planet hot spot; this confirms that the phase variation is due to an offset hot spot on the planet; (9) a retraction of the claimed eccentricity of this system due to the offset of secondary eclipse; and (10) high precision measurements of the parameters of this system.