Observation of the full 12-hour-long transit of the exoplanet HD 80606b

Abstract

We present new observations of a transit of the 111.4-day-period exoplanet HD 80606b. Due to this long orbital period and to the orientation of the eccentric orbit (e = 0.9), HD 80606b's transits last for about 12 hours. This makes the observation of a full transit practically impossible from a given ground-based observatory. With the Spitzer Space Telescope and its IRAC camera on the postcryogenic mission, we performed a 19-h photometric observation of HD 80606 that covers the full 2010 January 13-14 transit as well as off-transit references immediately before and after the event. We complement these photometric data by new spectroscopic observations that we simultaneously performed with SOPHIE at the Haute-Provence Observatory. This provides radial velocity measurements of the first half of the transit that was previously uncovered with spectroscopy. This new dataset allows the parameters of this singular planetary system to be significantly refined. We obtained a planet-to-star radius ratio R p /R * = 0.1001 ± 0.0006 that is more accurate but slightly lower than the one measured from previous ground observations in the optical. We found no astrophysical interpretations able to explain this difference between optical and infrared radii; we rather favor underestimated systematic uncertainties, maybe in the ground-based composite light curve. We detected a feature in the Spitzer light curve that could be due to a stellar spot. We also found a transit timing about 20 minutes earlier than the ephemeris prediction; this could be caused by actual transit-timing variations due to an additional body in the system, or again by underestimated systematic uncertainties. The actual angle between the spin-axis of HD 80606 and the normal to the planetary orbital plane is found to be near 40• thanks to the fit of the Rossiter-McLaughlin anomaly, with a sky-projected value λ = 42• ± 8• . This allows scenarios with aligned spin-orbit to be definitively rejected. Over the twenty planetary systems with measured spin-orbit angles, a few are misaligned; this is probably the signature of two different evolution scenarios for misaligned and aligned systems, depending whether or not they experienced gravitational interaction with a third body. As in the case of HD 80606, most of the planetary systems including a massive planet are tilted; this could be the signature of a separate evolution scenario for massive planets compared with Jupiter-mass planets.

Deformation and tidal evolution of close-in planets and satellites using a Maxwell viscoelastic rheology

“…Here, we apply our model to the planets HAT-P-34 b (Bakos et al 2012) and HD 80606 b (Hébrard et al 2010), both belonging to single-planet systems. The main difference between these two planets is their present orbital period, only 5.45 day for HAT-P-34 b, and about 111 day for HD 80606 b (Table 1).…”

Multiwavelength flux variations induced by stellar magnetic activity: effects on planetary transits

“…However, the infrared (IR) observations are affected by systematic effects that may compromise the measurements because these effects induce flux variations comparable to the depth of a planetary transit. For example, the 3.6 and 4.5 μm Spitzer/IRAC channels (InSb detectors) are affected by the pixel-phase effect (Reach et al 2005;Charbonneau et al 2005;MoralesCalderón et al 2006;Knutson et al 2008) due to the telescope jitter and intra-pixel variation in the sensitivity of the detector, which may cause a flux peak-to-peak amplitude of up to ∼1% (Beaulieu et al 2008;Hébrard et al 2010) or even higher (Désert et al 2011b;Fressin et al 2011), according to the exposure time. The light curves of the 5.8 and 8.0 μm channels (Si:As detectors) follow non-linear trends with time, called the ramp effect Knutson et al 2007a), caused by the trapping of electrons by the detector impurities (see Agol et al 2010 for further details), which produce mmag level flux variations in photometry.…”

Gran Telescopio Canarias OSIRIS transiting exoplanet atmospheric survey: detection of potassium in XO-2b from narrowband spectrophotometry

“…We used the three-parameter non-linear limb-darkening law, because it provides the best flexibility to capture the inherent non-linearity of the limb-darkening intensity profile and helps to avoid the deficient ATLAS model values near the limb (see Sing 2010, for more details). This law has now successfully been used to model high precision transit light curves including data from HST/NICMOS ), Spitzer (Hébrard et al 2010;Désert et al 2011), and CoRot. In the fits we also allowed the baseline flux level of each visit to linearly vary in time, which is described by the two fit-parameters.…”