Jan-Vincent Harre

Context. Recent developments in exoplanetary research highlight the importance of Love numbers in understanding the internal dynamics, formation, migration history, and potential habitability of exoplanets. Love numbers represent crucial parameters that gauge how exoplanets respond to external forces such as tidal interactions and rotational effects. By measuring these responses, insights into the internal structure, composition, and density distribution of exoplanets can be gained. The rate of apsidal precession of a planetary orbit is directly linked to the second-order fluid Love numbers. Thus, Love numbers can also offer valuable insights into the mass distribution of a planet. Aims. In this context, we aim to re-determine the orbital parameters of WASP-43b – in particular, the orbital period, eccentricity, and argument of the periastron – and its orbital evolution. We study the outcomes of the tidal interaction with the host star in order to identify whether tidal decay and periastron precession occur in the system. Methods. We observed WASP-43b with HARPS, whose data we present for the first time, and we also analysed the newly acquired JWST full-phase light curve. We jointly fit new and archival radial velocity and transit and occultation mid-times, including tidal decay, periastron precession, and long-term acceleration in the system. Results. We detected a tidal decay rate of Ṗ_a = (−l.99±0.50) ms yr⁻¹ and a periastron precession rate of ω = 0.1727_−0.0089^+0.0083)° d⁻¹ = (621.72_−32.04^+29.88)″ d⁻¹). This is the first time that both periastron precession and tidal decay are simultaneously detected in an exoplanetary system. The observed tidal interactions can neither be explained by the tidal contribution to apsidal motion of a non-aligned stellar or planetary rotation axis nor by assuming a non-synchronous rotation for the planet, and a value for the planetary Love number cannot be derived. Moreover, we excluded the presence of a second body (e.g. a distant companion star or a yet undiscovered planet) down to a planetary mass of ≳0.3 M_J and up to an orbital period of ≲3700 days. We leave the question of the cause of the observed apsidal motion open.

Context. Recent developments in exoplanetary research highlight the importance of Love numbers in understanding their internal dynamics, formation, migration history and their potential habitability. Love numbers represent crucial parameters that gauge how exoplanets respond to external forces such as tidal interactions and rotational effects. By measuring these responses, we can gain insights into the internal structure, composition, and density distribution of exoplanets. The rate of apsidal precession of a planetary orbit is directly linked to the second-order fluid Love number, thus we can gain valuable insights into the mass distribution of the planet. Aims. In this context, we aim to re-determine the orbital parameters of WASP-43b-in particular, orbital period, eccentricity, and argument of the periastron-and its orbital evolution. We study the outcomes of the tidal interaction with the host star:whether tidal decay and periastron precession are occurring in the system. Method. We observed the system with HARPS, whose data we present for the first time, and we also analyse the newly acquired JWST full-phase light curve. We fit jointly archival and new radial velocity and transit and occultation mid-times, including tidal decay, periastron precession and long-term acceleration in the system. Results. We detected a tidal decay rate of \dotP_a=(-1.99pm0.50) and a periastron precession rate of \dotomega=(0.1851+0.0070-0.0077)=(0.1727+0.0083-0.0089)deg/d=(621.72+29.88-32.04)arcsec/d. This is the first time that both periastron precession and tidal decay are simultaneously detected in an exoplanetary system. The observed tidal interactions can neither be explained by the tidal contribution to apsidal motion of a non-aligned stellar or planetary rotation axis nor by assuming non-synchronous rotation for the planet, and a value for the planetary Love number cannot be derived. [...]

Context. Hot Jupiters (HJs) with close-by planetary companions are rare, with only a handful of them having been discovered so far. This could be due to their suggested dynamical histories, which lead to the possible ejection of other planets. TOI-2109 b is special in this regard because it is the HJ with the closest relative separation from its host star, being separated by less than 2.3 stellar radii. Unexpectedly, transit timing measurements from recently obtained CHEOPS observations show low-amplitude transit-timing variations (TTVs). Aims. We aim to search for signs of orbital decay and to characterise the apparent TTVs in an attempt to gain information about a possible companion. Methods. We fitted the newly obtained CHEOPS light curves using TLCM and extracted the resulting mid-transit timings. Successively, we used these measurements in combination with TESS and archival photometric data and radial velocity (RV) data to estimate the rate of tidal orbital decay of TOI-2109 b, and also to characterise the TTVs using the N-body code TRADES and the photo-dynamical approach of PyTTV. Results. We find tentative evidence at 3σ for orbital decay in the TOI-2109 system when we correct the mid-transit timings using the best-fitting sinusoidal model of the TTVs. We do not detect additional transits in the available photometric data, but find evidence supporting the authenticity of the apparent TTVs, indicating a close-by, outer companion with P_c > 1.125 d. Due to the fast rotation of the star, the new planetary candidate cannot be detected in the available RV measurements, and its parameters can only be loosely constrained by our joint TTV and RV modelling. Conclusions. TOI-2109 could join a small group of rare HJ systems that host close-by planetary companions, only one of which (WASP-47 b) has an outer companion. More high-precision photometric measurements are necessary to confirm the existence of this planetary companion.

Transiting planets around young stars are hard to find due to the enhanced stellar activity. Only a few transiting planets have been detected around stars younger than 100 Myr. We initially detected a transit-like signal in the K2 light curve of a very cool M dwarf star (EPIC 211101996) in the Pleiades open cluster, with an estimated age of about 100 Myr. Our detailed analysis of the per-pixel light curves, detrending with the Wōtan software and transit search with the Transit Least Squares algorithm showed that the source of the signal is a contaminant source (Gaia DR3 66767847894609792) 20" west of the target. The V-like shape of its phase-folded light curve and eclipse depth of ~15% suggest that it is a grazing eclipsing binary. The contaminant has hitherto been listed as a single star, which we now identify as an eclipsing stellar binary with a period of about 6 days.

Transiting planets around young stars are hard to find due to the enhanced stellar activity. Only a few transiting planets have been detected around stars younger than 100 Myr. We initially detected a transit-like signal in the K2 light curve of a very cool M dwarf star (EPIC 211101996) in the Pleiades open cluster, with an estimated age of about 100 Myr. Our detailed analysis of the per-pixel light curves, detrending with the Wōtan software and transit search with the Transit Least Squares algorithm showed that the source of the signal is a contaminant source (Gaia DR3 66767847894609792) 20″ west of the target. The V-like shape of its phase-folded light curve and eclipse depth of ∼15% suggest that it is a grazing eclipsing binary. The contaminant has hitherto been listed as a single star, which we now identify as an eclipsing stellar binary with a period of about 6 days.

Context. Occultations are windows of opportunity to indirectly peek into the dayside atmosphere of exoplanets. High-precision transit events provide information on the spin-orbit alignment of exoplanets around fast-rotating hosts. Aims. We aim to precisely measure the planetary radius and geometric albedo of the ultra-hot Jupiter (UHJ) KELT-20 b along with the spin-orbit alignment of the system. Methods. We obtained optical high-precision transits and occultations of KELT-20 b using CHEOPS observations in conjunction with simultaneous TESS observations. We interpreted the occultation measurements together with archival infrared observations to measure the planetary geometric albedo and dayside temperatures. We further used the host star’s gravity-darkened nature to measure the system’s obliquity. Results. We present a time-averaged precise occultation depth of 82 ± 6 ppm measured with seven CHEOPS visits and 131₋₇⁺⁸ from the analysis of all available TESS photometry. Using these measurements, we precisely constrain the geometric albedo of KELT-20 b to 0.26 ± 0.04 and the brightness temperature of the dayside hemisphere to 2566₋₈₀⁺⁷⁷ K. Assuming Lambertian scattering law, we constrain the Bond albedo to 0.36_−0.05^+0.04 along with a minimal heat transfer to the night side (ϵ = 0.14_−0.10^+0.13). Furthermore, using five transit observations we provide stricter constraints of 3 9 ± 1 1 deg on the sky-projected obliquity of the system. Conclusions. The aligned orbit of KELT-20 b is in contrast to previous CHEOPS studies that have found strongly inclined orbits for planets orbiting other A-type stars. The comparably high planetary geometric albedo of KELT-20 b corroborates a known trend of strongly irradiated planets being more reflective. Finally, we tentatively detect signs of temporal variability in the occultation depths, which might indicate variable cloud cover advecting onto the planetary day side.

Ongoing observing projects like the James Webb Space Telescope and future missions offer the chance to characterize Earth-like exoplanetary atmospheres. Thereby, M dwarfs are preferred targets for transit observations, for example, due to their favorable planet–star contrast ratio. However, the radiation and particle environment of these cool stars could be far more extreme than what we know from the Sun. Thus, knowing the stellar radiation and particle environment and its possible influence on detectable biosignatures—in particular, signs of life like ozone and methane—is crucial to understanding upcoming transit spectra. In this study, with the help of our unique model suite INCREASE, we investigate the impact of a strong stellar energetic particle event on the atmospheric ionization, neutral and ion chemistry, and atmospheric biosignatures of TRAPPIST-1e. Therefore, transit spectra for six scenarios are simulated. We find that a Carrington-like event drastically increases atmospheric ionization and induces substantial changes in ion chemistry and spectral transmission features: all scenarios show high event-induced amounts of nitrogen dioxide (i.e., at 6.2 μm), a reduction of the atmospheric transit depth in all water bands (i.e., at 5.5–7.0 μm), a decrease of the methane bands (i.e., at 3.0–3.5 μm), and depletion of ozone (i.e., at ∼9.6 μm). Therefore, it is essential to include high-energy particle effects to correctly assign biosignature signals from, e.g., ozone and methane. We further show that the nitric acid feature at 11.0–12.0 μm, discussed as a proxy for stellar particle contamination, is absent in wet-dead atmospheres.

Tidal orbital decay plays a vital role in the evolution of hot Jupiter systems. As of now, this has only been observationally confirmed for the WASP-12 system. There are a few other candidates, including WASP-4 b, but no conclusive result could be obtained for these systems as of yet. In this study, we present an analysis of new TESS data of WASP-4 b together with archival data, taking the light–time effect (LTE) induced by the second planetary companion into account as well. We make use of three different Markov chain Monte Carlo models: a circular orbit with a constant orbital period, a circular orbit with a decaying orbit, and an elliptical orbit with apsidal precession. This analysis is repeated for four cases. The first case features no LTE correction, with the remaining three cases featuring three different timing correction approaches because of the large uncertainties of the ephemeris of planet c. Comparison of these models yields no conclusive answer to the cause of WASP-4 b’s apparent transit timing variations. A broad range of values of the orbital decay and apsidal precession parameters are possible, depending on the LTE correction. However, the LTE caused by planet c can explain on its own—in full—the observed transit timing variations of planet b, with no orbital decay or apsidal precession being required at all. This work highlights the importance of continued photometric and spectroscopic monitoring of hot Jupiters.

Tidal orbital decay plays a vital role in the evolution of hot Jupiter systems. As of now, this was only observationally confirmed for the WASP-12 system. There are a few other candidates, including WASP-4 b, but no conclusive result could be obtained for these systems as of yet. In this study, we present an analysis of new TESS data of WASP-4 b together with archival data, taking the light-time effect (LTE), induced by the second planetary companion, into account as well. We make use of three different Markov-Chain-Monte-Carlo models; a circular orbit with a constant orbital period, a circular orbit with a decaying orbit, and an elliptical orbit with apsidal precession. This analysis is repeated for four cases. The first case features no LTE correction, with the remaining three cases featuring three different timing correction approaches. Comparison of these models yields no conclusive answer to the cause of WASP-4\,b's apparent transit timing variations. A broad range of values of the orbital decay and apsidal precession parameters are possible, depending on the LTE correction. This work highlights the importance of continued photometric and spectroscopic monitoring of hot Jupiters.