Discovery of a substellar companion in the TESS light curve of the $\delta$ Scuti/$\gamma$ Doradus hybrid pulsator HD 31221

Abstract

Close-in, sub-stellar companions to $\delta$ Scuti type stars present a highly suitable testbed for examining how planetary-mass objects can influence stellar pulsations. We aim to constrain the mass of HD 31221 b, probe its atmosphere, and demonstrate how it affects the pulsational pattern of its host, HD 31221. We made use of the available data from the short-cadence Transiting Exoplanet Survey Satellite (TESS). We modeled the nine observed transits and the out-of-phase variations, including Doppler beaming, ellipsoidal variations, and the reflection effect. We also incorporated ground-based photometry from the MuSCAT2 imager installed at the 1.52 m Telescopio Carlos Sanchez in the Teide Observatory, Spain. We found HD 31221 b to have an orbital period of $4.66631\pm 0.00011$ days, with a radius of $1.32\pm 0.14$ R${}_J$ and a mass of $11.5\pm 10.3$ M${}_J$ (from the ellipsoidal effect), making it consistent with either a brown dwarf or a giant planet. As HD 31221 is a rapid rotator ($v\sin I_{\star }=175.31\pm 1.74$ km s${}^{-1}$), we deduced the spin-orbit misalignment to be $\lambda =-121.6\pm 14.4^{\circ }$ and $I_{\star }=55.9\pm 11.3^{\circ }$. The phase curve is dominated by the reflection effect, with a geometric albedo of $1.58\pm 0.50$. We also found evidence that HD 31221 is a $\delta$ Scuti/$\gamma$ Doradus hybrid pulsator. There are three cases for which the $3$rd, $85$th, and $221$st orbital harmonics almost exactly coincide with peaks in the Fourier spectrum of the star, hinting at tidally perturbed stellar oscillations. HD 31221 b is the third substellar object that is found to be disrupting the pulsations of its host, following HAT-P-2 and WASP-33. Additional photometric observations by CHEOPS and/or PLATO can be used to further constrain its mass and provide a more in-depth analysis of its atmosphere.

arXiv commentAccepted for publication as a Letter in A&A, 12 pages, 10 figures

References in corpus (47)

• Astropy: A Community Python Package for Astronomy
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• The Transiting Exoplanet Survey Satellite
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• Analytic Lightcurves for Planetary Transit Searches
• The PLATO 2.0 Mission
• astroquery: An Astronomical Web-Querying Package in Python
• Homogeneous studies of transiting extrasolar planets. IV. Thirty systems with space-based light curves
• The Kepler characterization of the variability among A- and F-type stars. I. General overview
• Parameter Estimation from Time-Series Data with Correlated Errors: A Wavelet-Based Method and its Application to Transit Light Curves
• Line-profile tomography of exoplanet transits -- II. A gas-giant planet transiting a rapidly-rotating A5 star
• KELT-1b: A Strongly Irradiated, Highly Inflated, Short Period, 27 Jupiter-mass Companion Transiting a mid-F Star
• The CHEOPS mission
• Exoplanetary Spin-Orbit Alignment: Results from the Ensemble of Rossiter-McLaughlin Observations
• A giant planet undergoing extreme ultraviolet irradiation by its hot massive-star host
• Planetary nebulae seen with TESS: Discovery of new binary central star candidates from Cycle 1
• Hybrid gamma Doradus - delta Scuti pulsators: New insights into the physics of the oscillations from Kepler observations
• HD147506b: A Super-Massive Planet in an Eccentric Orbit Transiting a Bright Star
• Photometric detection of non-transiting short-period low-mass companions through the beaming, ellipsoidal and reflection effects in Kepler and CoRoT lightcurves
• Beaming Binaries - a New Observational Category of Photometric Binary Stars
• Transit Lightcurves of Extrasolar Planets Orbiting Rapidly-Rotating Stars
• The hot dayside and asymmetric transit of WASP-189b seen by CHEOPS
• Multicolour photometry for exoplanet candidate validation
• Kepler photometry of KIC 10661783: a binary star with total eclipses and delta Scuti pulsations
• WASP-33: The first delta Scuti exoplanet host star
• Visible-light Phase Curves from the Second Year of the TESS Primary Mission
• Confirmation of Hot Jupiter Kepler-41b via Phase Curve Analysis
• TESS unveils the phase curve of WASP-33b. Characterization of the planetary atmosphere and the pulsations from the star
• KELT-9 b's Asymmetric TESS Transit Caused by Rapid Stellar Rotation and Spin-Orbit Misalignment
• Discovery of $\beta$ Cep pulsations in the eclipsing binary V453 Cygni
• MASCARA-1 b: A hot Jupiter transiting a bright $m_V=8.3$ A-star in a misaligned orbit
• Spi-OPS: Spitzer and CHEOPS confirm the near-polar orbit of MASCARA-1 b and reveal a hint of dayside reflection
• Speckle interferometry at SOAR in 2016 and 2017
• Asteroseismology of KIC 11754974: a high-amplitude SX Phe pulsator in a 343-day binary system
• Tidally perturbed pulsations in the pre-main sequence $\delta$ Scuti binary RS Cha
• Binarity and multiperiodicity in high-amplitude delta Scuti stars
• The stable climate of KELT-9b
• Planet-Induced Stellar Pulsations in HAT-P-2's Eccentric System
• The TESS Phase Curve of KELT-1b Suggests a High Dayside Albedo
• The GAPS Programme with HARPS-N at TNG. XXXI. The WASP-33 system revisited with HARPS-N
• CHEOPS finds KELT-1b darker than expected in visible light: Discrepancy between the CHEOPS and TESS eclipse depths
• Dealing With $\delta$-Scuti Variables: Transit Light Curve Analysis of Planets Orbiting Rapidly-Rotating, Seismically Active A/F Stars
• Power of wavelets in analyses of transit and phase curves in the presence of stellar variability and instrumental noise. II. Accuracy of the transit parameters
• Tidally Perturbed Oblique Pulsations in the Hierarchical Triple System V1031 Orionis
• Gravity darkening and tidally perturbed stellar pulsation in the misaligned exoplanet system WASP-33
• Efficient and precise transit light curves for rapidly-rotating, oblate stars
• TESS search for substellar companions through pulsation timing of $\delta$ Scuti stars. I. Discovery of companions around Chang 134 and V393 Car

Cited by in corpus (4)

• The phase curve of the ultra-hot Jupiter WASP-167b as seen by TESS
• The coevolution of migrating planets and their pulsating stars through episodic resonance locking
• Pulsation in TESS Objects of Interest
• CHEOPS observations confirm nodal precession in the WASP-33 system