The EBLM project. VII. Spin-orbit alignment for the circumbinary planet host EBLM J0608-59 A/TOI-1338 A

Abstract

A dozen short-period detached binaries are known to host transiting circumbinary planets. In all circumbinary systems so far, the planetary and binary orbits are aligned within a couple of degrees. However, the obliquity of the primary star, which is an important tracer of their formation, evolution, and tidal history, has only been measured in one circumbinary system until now. EBLM J0608-59/TOI-1338 is a low-mass eclipsing binary system with a recently discovered circumbinary planet identified by TESS. Here, we perform high-resolution spectroscopy during primary eclipse to measure the projected stellar obliquity of the primary component. The obliquity is low, and thus the primary star is aligned with the binary and planetary orbits with a projected spin-orbit angle $\beta =2.8\pm 17.1$ deg. The rotation period of $18.1\pm 1.6$ days implied by our measurement of $v\sin i_{\star }$ suggests that the primary has not yet pseudo-synchronized with the binary orbit, but is consistent with gyrochronology and weak tidal interaction with the binary companion. Our result, combined with the known coplanarity of the binary and planet orbits, is suggestive of formation from a single disc. Finally, we considered whether the spectrum of the faint secondary star could affect our measurements. We show through simulations that the effect is negligible for our system, but can lead to strong biases in $v\sin i_{\star }$ and $\beta$ for higher flux ratios. We encourage future studies in eclipse spectroscopy test the assumption of a dark secondary for flux ratios $\gtrsim 1$ ppt.

arXiv comment7 pages, 3 figures. Accepted in MNRAS. Fixed a few typos

References in corpus (34)

• emcee: The MCMC Hammer
• Accurate masses and radii of normal stars: modern results and applications
• Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics
• The WASP Project and the SuperWASP Cameras
• SparsePak: A Formatted Fiber Field Unit for The WIYN Telescope Bench Spectrograph. I. Design, Construction, and Calibration
• The Occurrence and Architecture of Exoplanetary Systems
• Kepler-16: A Transiting Circumbinary Planet
• EXOFAST: A fast exoplanetary fitting suite in IDL
• Kepler-47: A Transiting Circumbinary Multi-Planet System
• A new list of thorium and argon spectral lines in the visible
• The Formation of Close Binary Systems by Dynamical Interactions and Orbital Decay
• 55 Cancri (Copernicus): A Multi-Planet System with a Hot Super-Earth and a Jupiter Analogue
• 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
• Misaligned spin and orbital axes cause the anomalous precession of DI Herculis
• The EBLM Project I-Physical and orbital parameters, including spin-orbit angles, of two low-mass eclipsing binaries on opposite sides of the Brown Dwarf limit
• The Rossiter-McLaughlin effect in Exoplanet Research
• Asteroseismic detection of latitudinal differential rotation in 13 Sun-like stars
• The spin axes orbital alignment of both stars within the eclipsing binary system V1143Cyg using the Rossiter-McLaughlin effect
• The EBLM Project IV. Spectroscopic orbits of over 100 eclipsing M dwarfs masquerading as transiting hot-Jupiters
• TOI-1338: TESS' First Transiting Circumbinary Planet
• The BEBOP radial-velocity survey for circumbinary planets I. Eight years of CORALIE observations of 47 single-line eclipsing binaries and abundance constraints on the masses of circumbinary planets
• Two Upper Limits on the Rossiter-McLaughlin Effect, with Differing Implications: WASP-1 has a High Obliquity and WASP-2 is Indeterminate
• Comparison of the power-2 limb-darkening law from the Stagger-grid to Kepler light curves of transiting exoplanets
• Spin-Orbit Alignment for the Circumbinary Planet Host Kepler-16A
• The BANANA project. V. Misaligned and precessing stellar rotation axes in CV Velorum
• Evidence for Spin-orbit Alignment in the TRAPPIST-1 System
• Modelling the Rossiter-McLaughlin Effect: Impact of the Convective Centre-to-Limb Variations in the Stellar Photosphere
• The EBLM Project VI. The mass and radius of five low-mass stars in F+M binaries discovered by the WASP survey
• The binary mass ratios of circumbinary planet hosts
• Doppler imaging of stellar surface structure - XXIV. The lithium-rich single K-giants DP Canum Venaticorum and DI Piscium
• Tracking the spin axes orbital alignment in selected binary systems - Torun Rossiter-McLaughlin effect survey
• Lithium enrichment on the single active K1-giant DI Piscium -- Possible joint origin of differential rotation and Li enrichment

Cited by in corpus (10)

• Radial-velocity discovery of a second planet in the TOI-1338/BEBOP-1 circumbinary system
• Orbital misalignment of the super-Earth $\pi$ Men c with the spin of its star
• The spin-orbit alignment of visual binaries
• THE BANANA PROJECT. VI. Close double stars are well aligned with noticeable exceptions; results from an ensemble study using apsidal motion and Rossiter-McLaughlin measurements
• The EBLM project X. Benchmark masses, radii and temperatures for two fully convective M-dwarfs using K2
• TIC-320687387 B: a long-period eclipsing M-dwarf close to the hydrogen burning limit
• NGTS-EB-7, an eccentric, long-period, low-mass eclipsing binary
• Orbits of the TOI-1338 and TIC-172900988 systems
• Projected spin-orbit alignments from Kepler asteroseismology and Gaia astrometry
• The EBLM Project XVIII. 3D Obliquities of Five Low-Mass Eclipsing Binaries