HD 210058 b and BD+37 4838 b: A precessing eccentric hot Jupiter and a misaligned substellar companion around two A-type stars

Z. Balkóová; J. Žák; M. Skarka; M. C. Johnson; A. W. Mann; M. G. Barber; P. Gajdoš; T. G. Beatty; M. A. Kroft; I. Ilyin; P. Kabáth

arXiv · 2611.00378

HD 210058 b and BD+37 4838 b: A precessing eccentric hot Jupiter and a misaligned substellar companion around two A-type stars

Z. Balkóová·J. Žák·M. Skarka·M. C. Johnson·A. W. Mann·M. G. Barber·P. Gajdoš·T. G. Beatty·M. A. Kroft·I. Ilyin·P. Kabáth

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Abstract

The number of A- and F-type stars known to host exoplanets is relatively low, as is the number of planets with measured spin-orbit angle, which is the angle between the planet's orbital axis and the star's rotational axis. Expanding the sample of such systems is important for constraining the formation and migration mechanisms of close-in giant planets around early-type stars. We aim to measure the sky-projected spin-orbit angles of HD~210058b (TOI-1355b) and BD+37~4838b (TOI-1414b), two objects still listed as candidate exoplanets, and to assess the planetary nature of these systems. Both of their host stars are fast rotators. We analyzed TESS photometry together with transit time-series of HARPS-N spectra. For both objects, we created cross-correlation functions from the spectra to analyze Doppler tomography and detect and model the Doppler shadow, while we also used the photometric observations to refine a number of previously poorly constrained photometric and spectroscopic parameters of both the host stars and the companions. When possible, we used the derived results to constrain the companion masses. We verified the planetary and substellar nature for both objects respectively. We report HD~210058~b to be a giant hot Jupiter with a mass of 10 M_Jup, residing on a slightly misaligned orbit with the sky-projected spin-orbit angle λ=-32 -6 +4 deg. Archival photometry reveals continuously changing inclination and impact parameter, pointing to a nodal precession with period of 860 yr, and giving availability of only about six upcoming years for any further transit observations. The second target, BD+37~4838~b, orbits a hybrid γ~Dor-δ~Sct pulsator on a misaligned orbit with λ=56.9 +1.4 -2.3 deg. Since we could not reliably recover its mass, we only report an upper limit of approx. 24.3 M_Jup, leaving the possible planetary nature of this object unresolved.

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Z. Balkóová, J. Žák, M. Skarka, M. C. Johnson, A. W. Mann, M. G. Barber, P. Gajdoš, T. G. Beatty, M. A. Kroft, I. Ilyin, P. Kabáth. 2026-10-30. HD 210058 b and BD+37 4838 b: A precessing eccentric hot Jupiter and a misaligned substellar companion around two A-type stars. https://arxiv.org/abs/2611.00378

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