The California-Kepler Survey. XI. A Survey of Chromospheric Activity through the Lens of Precise Stellar Properties

Isaacson, Howard; Kane, Stephen R.; Carter, Brad; Howard, Andrew W.; Weiss, Lauren; Petigura, Erik A.; Fulton, Benjamin

doi:10.3847/1538-4357/ad077b

Cited by 5 publications

(1 citation statement)

References 85 publications

(177 reference statements)

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“…A possible cause of this discrepancy in rotation period measurements is differential rotation, similar to that observed for the known exoplanet host HD 219134 (Johnson et al 2016). Furthermore, there is growing evidence that spectroscopic and photometric rotation period measurements do not always agree, possibly the result of activity differences in the chromosphere and photosphere (Lafarga et al 2021;Schöfer et al 2022;Isaacson et al 2024). However, there are several other pieces of information to note here.…”

Section: Stellar Propertiesmentioning

confidence: 61%

A Perfect Tidal Storm: HD 104067 Planetary Architecture Creating an Incandescent World

Kane,

Fetherolf,

et al. 2024

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The discovery of planetary systems beyond the solar system has revealed a diversity of architectures, most of which differ significantly from our system. The initial detection of an exoplanet is often followed by subsequent discoveries within the same system as observations continue, measurement precision is improved, or additional techniques are employed. The HD 104067 system is known to consist of a bright K-dwarf host star and a giant planet in a ∼55 days period eccentric orbit. Here we report the discovery of an additional planet within the HD 104067 system, detected through the combined analysis of radial velocity (RV) data from the High Resolution Echelle Spectrometer and High Accuracy Radial velocity Planet Searcher instruments. The new planet has a mass similar to Uranus and is in an eccentric ∼14 days orbit. Our injection-recovery analysis of the RV data exclude Saturn-mass and Jupiter-mass planets out to 3 au and 8 au, respectively. We further present Transiting Exoplanet Survey Satellite observations that reveal a terrestrial planet candidate (R p = 1.30 ± 0.12 R ⊕) in a ∼2.2 days period orbit. Our dynamical analysis of the three planet model shows that the two outer planets produce significant eccentricity excitation of the inner planet, resulting in tidally induced surface temperatures as high as ∼2600 K for an emissivity of unity. The terrestrial planet candidate may therefore be caught in a tidal storm, potentially resulting in its surface radiating at optical wavelengths.

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Section: Stellar Propertiesmentioning

confidence: 61%

A Perfect Tidal Storm: HD 104067 Planetary Architecture Creating an Incandescent World

Kane,

Fetherolf,

et al. 2024

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Equilibrium tides and magnetic activity in stars with close-by massive planets

Lanza,

Breton

2024

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WASP-18 is an F6V star that hosts a planet with a mass of $ 10$ Jupiter masses and an orbital period of $ 0.94$ days. In spite of its relatively fast rotation and young age, the star remains undetected in X-rays, thus implying a very low level of magnetic activity. To account for such unexpected properties, we propose a mechanism that modifies the internal stratification and the photospheric magnetic activity of a late-type main sequence star with a close-by massive planet based on the action of the equilibrium tide. We speculate that the horizontal flow produced by the equilibrium tide may interact with the convective plumes in the overshoot layer below the stellar outer convective envelope. The interaction is characterised by a very high Reynolds number ($Re $), leading to the development of turbulent boundary layers at the surface of such structures, whereas turbulent wakes extend over most of the overshoot layer that they straddle. We propose that such a tidally induced turbulence can lead to a reduction of the filling factor of the downdrafts in the overshoot layer. As a consequence, the absolute value of the sub-adiabatic gradient increases in that layer hindering the emergence of magnetic flux tubes responsible for the formation of photospheric starspots. We conjecture that this process is occurring in WASP-18, thus providing a possible mechanism to account for the very low level of magnetic activity observed for such a planet host.

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The GAPS Programme at TNG

Nardiello,

Akana Murphy,

Spinelli

et al. 2024

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Small-sized ($<4$ $R_ oplus $) exoplanets in tight orbits around young stars (10--1000 Myr) give us the opportunity to investigate the mechanisms that led to their formation, the evolution of their physical and orbital properties, and, in particular, their atmospheres. Thanks to the all-sky survey carried out by the spacecraft, many of these exoplanets have been discovered, and have subsequently been characterized with dedicated follow-up observations. In the context of a collaboration among the Global Architecture of Planetary Systems (GAPS) team, the TESS-Keck Survey (TKS) team, and the California Planet Search (CPS) team, we measured ---with a high level of precision--- the mass and the radius of TOI-1430 b, a young ($ 700$ Myr) exoplanet with an escaping He atmosphere orbiting the K-dwarf star HD 235088 (TOI-1430). By adopting appropriate stellar parameters, which were measured in this work, we were able to simultaneously model the signals due to strong stellar activity and the transiting planet TOI-1430 b in both photometric and spectroscopic series. This allowed us to measure both the radius and mass (and consequently the density) of the planet with high precision, and to reconstruct the evolution of its atmosphere. TOI-1430 is an active K-dwarf star born $700 150$ Myr ago, with a rotation period of rot 12$ days. This star hosts a mini-Neptune, whose orbital period is b 0.000004$ days. Thanks to long-term photometric and spectroscopic monitoring of this target performed with TESS, HARPS-N, HIRES, and APF, we estimate a radius of P,b oplus $, a mass of $M_ P,b oplus $, and thus a planetary density of $ b oplus $. TOI-1430 b is therefore a low-density mini-Neptune with an extended atmosphere, and is at the edge of the radius gap. Because this planet is known to have an evaporating atmosphere of He, we reconstructed its atmospheric history. Our analysis supports the scenario in which, shortly after its birth, TOI-1430 b was super-puffy, with a radius $5 and a mass $1.5 the values of today; in $ 200$ Myr from now, TOI-1430 b should lose its envelope, showing its Earth-size core. We also looked for signals from a second planet in the spectroscopic and photometric series, without detecting any.

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The California-Kepler Survey. XI. A Survey of Chromospheric Activity through the Lens of Precise Stellar Properties

Cited by 5 publications

References 85 publications

A Perfect Tidal Storm: HD 104067 Planetary Architecture Creating an Incandescent World

A Perfect Tidal Storm: HD 104067 Planetary Architecture Creating an Incandescent World

Equilibrium tides and magnetic activity in stars with close-by massive planets

The GAPS Programme at TNG

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