Refined architecture of the WASP-8 system: a cautionary tale for traditional Rossiter-McLaughlin analysis

Abstract

Probing the trajectory of a transiting planet across the disk of its star through the analysis of its Rossiter-McLaughlin effect can be used to measure the differential rotation of the host star and the true obliquity of the system. Highly misaligned systems could be particularly conducive to these mesurements, which is why we reanalysed the HARPS transit spectra of WASP-8b using the 'Rossiter-McLaughlin effect reloaded' (reloaded RM) technique. This approach allows us to isolate the local stellar CCF emitted by the planet-occulted regions. As a result we identified a $\sim$35% variation in the local CCF contrast along the transit chord, which might trace a deepening of the stellar lines from the equator to the poles. Whatever its origin, such an effect cannot be detected when analyzing the RV centroids of the disk-integrated CCFs through a traditional velocimetric analysis of the RM effect. Consequently it injected a significant bias into the results obtained by Queloz et al. (2010) for the projected rotational velocity $v_{eq}\sin i_{\star }$ (1.59$\stackrel{+0.08}{{}_{-0.09}}$ km/s) and the sky-projected obliquity $\lambda$ (-123.0${\stackrel{+3.4}{{}_{-4.4}}}^{\circ }$). Using our technique, we measured these values to be $v_{eq}\sin i_{\star }$ = 1.90$\pm$0.05 km/s and $\lambda$ = -143.0${\stackrel{+1.6}{{}_{-1.5}}}^{\circ }$. We found no compelling evidence for differential rotation of the star, although there are hints that WASP-8 is pointing away from us with the stellar poles rotating about 25% slower than the equator. Measurements at higher accuracy during ingress/egress will be required to confirm this result. In contrast to the traditional analysis of the RM effect, the reloaded RM technique directly extracts the local stellar CCFs, allowing us to analyze their shape and to measure their RV centroids, unbiased by variations in their contrast or FWHM.

arXiv commentAccepted for publication in A&A. 12 pages

References in corpus (22)

• Cosmological parameters from SDSS and WMAP
• Analytic Lightcurves for Planetary Transit Searches
• batman: BAsic Transit Model cAlculatioN in Python
• EXOFAST: A fast exoplanetary fitting suite in IDL
• Obliquities of Hot Jupiter host stars: Evidence for tidal interactions and primordial misalignments
• Improving the Efficiency of Markov Chain Monte Carlo for Analyzing the Orbits of Extrasolar Planets
• Friends of Hot Jupiters I: A Radial Velocity Search for Massive, Long-Period Companions to Close-In Gas Giant Planets
• The Rossiter-McLaughlin effect and analytic radial velocity curves for transiting extrasolar planetary systems
• PASTIS: Bayesian extrasolar planet validation. I. General framework, models, and performance
• The Rossiter-McLaughlin effect of CoRoT-3b & HD189733b
• Improved Modeling of the Rossiter-McLaughlin Effect for Transiting Exoplanets
• Line-profile tomography of exoplanet transits I: The Doppler shadow of HD 189733b
• The Rossiter-McLaughlin effect reloaded: Probing the 3D spin-orbit geometry, differential stellar rotation, and the spatially-resolved stellar spectrum of star-planet systems
• WASP-8b: a retrograde transiting planet in a multiple system
• Analytic Description of the Rossiter-McLaughlin Effect for Transiting Exoplanets: Cross-Correlation Method and Comparison with Simulated Data
• Differential rotation in K, G, F and A stars
• Rossiter--McLaughlin models and their effect on estimates of stellar rotation, illustrated using six WASP systems
• New analytical expressions of the Rossiter-McLaughlin effect adapted to different observation techniques
• Spin-Orbit angle distribution and the origin of (mis)aligned hot Jupiters
• High-resolution Imaging of Transiting Extrasolar Planetary systems (HITEP). I. Lucky imaging observations of 101 systems in the southern hemisphere
• Modelling the Rossiter-McLaughlin Effect: Impact of the Convective Centre-to-Limb Variations in the Stellar Photosphere
• Doppler tomography of transiting exoplanets: A prograde, low-inclined orbit for the hot Jupiter CoRoT-11b

Cited by in corpus (36)

• Nightside condensation of iron in an ultra-hot giant exoplanet
• Stellar obliquities in exoplanetary systems
• Orbital misalignment of the Neptune-mass exoplanet GJ 436b with the spin of its cool star
• Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS) I. Detection of hot neutral sodium at high altitudes on WASP-49b
• Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS) III. Atmospheric structure of the misaligned ultra-hot Jupiter WASP-121b
• The Rossiter-McLaughlin effect in Exoplanet Research
• A Preponderance of Perpendicular Planets
• Mass loss rate and local thermodynamic state of KELT-9 b thermosphere from the hydrogen Balmer series
• The GAPS Programme with HARPS-N at TNG XVI: Measurement of the Rossiter-McLaughlin effect of the transiting planetary systems HAT-P-3, HAT-P-12, HAT-P-22, WASP-39 and WASP-60
• Detection of Na, K, and H$\alpha$ absorption in the atmosphere of WASP-52b using ESPRESSO
• The atmosphere of HD 209458b seen with ESPRESSO. No detectable planetary absorptions at high resolution
• DREAM I. Orbital architecture orrery
• The Rossiter-McLaughlin effect Revolutions: An ultra-short period planet and a warm mini-Neptune on perpendicular orbits
• A Tendency Toward Alignment in Single-Star Warm Jupiter Systems
• Is there NaI in the atmosphere of HD 209458b? Effect of the centre-to-limb variation and Rossiter-McLaughlin effect in transmission spectroscopy studies
• WASP-127b: A misaligned planet with a partly cloudy atmosphere and tenuous sodium signature seen by ESPRESSO
• Nearly Polar orbit of the sub-Neptune HD3167 c: Constraints on a multi-planet system dynamical history
• The TESS-Keck Survey IV: A Retrograde, Polar Orbit for the Ultra-Low-Density, Hot Super-Neptune WASP-107b
• DREAM II. The spin-orbit angle distribution of close-in exoplanets under the lens of tides
• The polar orbit of the warm Neptune GJ436b seen with VLT/ESPRESSO
• Orbital misalignment of the super-Earth $\pi$ Men c with the spin of its star
• MASCARA-4 b/bRing-1b - A retrograde hot Jupiter around the bright A3V star HD 85628
• Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS) VII. Detection of sodium on the long-transiting inflated sub-Saturn KELT-11 b
• Obliquity measurement and atmospheric characterization of the WASP-74 planetary system
• The Spin-Orbit Alignment of 8 Warm Gas Giant Systems
• Can we detect the stellar differential rotation of WASP-7 through theRossiter-McLaughlin observations?
• The Hot Neptune WASP-166~b with ESPRESSO I: Refining the Planetary Architecture and Stellar Variability
• WASP-131 b with ESPRESSO I: A bloated sub-Saturn on a polar orbit around a differentially rotating solar-type star
• Creating retrogradely orbiting planets by prograde stellar fly-bys
• Rossiter-McLaughlin detection of the 9-month period transiting exoplanet HIP41378 d
• The First Spin-Orbit Obliquity of an M dwarf/brown dwarf System: An eccentric and aligned TOI-2119 b
• Looking For Timing Variations in the Transits of 16 Exoplanets
• Three Saturn-mass planets transiting F-type stars revealed with TESS and HARPS
• Exploring the stellar surface phenomena of WASP-52 and HAT-P-30 with ESPRESSO
• Variability of Known Exoplanet Host Stars Observed by TESS
• TOI-858 B b: A hot Jupiter on a polar orbit in a loose binary