Zodiacal exoplanets in time – XI. The orbit and radiation environment of the young M dwarf-hosted planet K2-25b

Gaidos, Eric; Hirano, Teruyuki; Wilson, D. J.; Rockcliffe, Keighley E.; Newton, Elisabeth R.; Feiden, Gregory A.; Krishnamurthy, Vigneshwaran; Harakawa, Hiroki; Hodapp, Klaus W.; Ishizuka, Masato; Jacobson, Shane; Konishi, Mihoko; Kotani, Takayuki; Kudo, Tomoyuki; Kurokawa, Takashi; Kuzuhara, Masayuki; Nishikawa, Jun; Omiya, Masashi; Serizawa, Takuma; Tamura, Motohide; Ueda, Akitoshi; Vievard, Sébastien

doi:10.1093/mnrasl/slaa136

Cited by 28 publications

(16 citation statements)

References 41 publications

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“…During the preparation of this manuscript, we became aware that Gaidos et al (2020) performed a complimentary analysis of the K2-25b system to constrain its obliquity using the IRD on the 8.2 m Subaru Telescope. Although the submissions of these complementary studies were coordinated between the groups, the data analyses and interpretations were performed independently.…”

Section: Independent Analysis Of K2-25b By Irdmentioning

confidence: 99%

The Habitable Zone Planet Finder Reveals a High Mass and Low Obliquity for the Young Neptune K2-25b

Stefánsson

Mahadevan

Maney

et al. 2020

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Using radial velocity data from the Habitable Zone Planet Finder, we have measured the mass of the Neptune-sized planet K2-25b, as well as the obliquity of its M4.5 dwarf host star in the 600-800 Myr Hyades cluster. This is one of the youngest planetary systems for which both of these quantities have been measured and one of the very few M dwarfs with a measured obliquity. Based on a joint analysis of the radial velocity data, time-series photometry from the K2 mission, and new transit light curves obtained with diffuser-assisted photometry, the planet's radius and mass are 3.44±0.12 R ⊕ and -+ Å M 24.5 5.2 5.7. These properties are compatible with a rocky core enshrouded by a thin hydrogen-helium atmosphere (5% by mass). We measure an orbital eccentricity of e=0.43±0.05. The skyprojected stellar obliquity is λ=3°±16°, compatible with spin-orbit alignment, in contrast to other "hot Neptunes" that have been studied around older stars.

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Section: Independent Analysis Of K2-25b By Irdmentioning

confidence: 99%

The Habitable Zone Planet Finder Reveals a High Mass and Low Obliquity for the Young Neptune K2-25b

Stefánsson

Mahadevan

Maney

et al. 2020

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“…2020). This experiment has been challenging, mainly because of limitations in our instruments and our theories (e.g., Cubillos et al 2017;Kasper et al 2020;Gaidos et al 2020;Bean et al 2021).…”

Section: Introductionmentioning

confidence: 99%

p-winds: An open-source Python code to model planetary outflows and upper atmospheres

Santos

Vidotto

Vissapragada

et al. 2022

A&A

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Atmospheric escape is considered to be one of the main channels for evolution in sub-Jovian planets, particularly in their early lives. While there are several hypotheses proposed to explain escape in exoplanets, testing them with atmospheric observations remains a challenge. In this context, high-resolution transmission spectroscopy of transiting exoplanets for the metastable helium triplet (He 2 3 S) at 1 083 nm has emerged as a reliable technique for observing and measuring escape. To aid in the prediction and interpretation of metastable He transmission spectroscopy observations, we developed the code p-winds. This is an open-source, fully documented, scalable Python implementation of the one-dimensional, purely H+He Parker wind model for upper atmospheres coupled with ionization balance, ray-tracing, and radiative transfer routines. We demonstrate an atmospheric retrieval by fitting p-winds models to the observed metastable He transmission spectrum of the warm Neptune HAT-P-11 b and take the variation in the in-transit absorption caused by transit geometry into account. For this planet, our best fit yields a total atmospheric escape rate of approximately 2.5 × 10 10 g s −1 and an outflow temperature of 7200 K. The range of retrieved mass loss rates increases significantly when we let the H atom fraction be a free parameter, but its posterior distribution remains unconstrained by He observations alone. The stellar host limb darkening does not have a significant impact on the retrieved escape rate or outflow temperature for HAT-P-11 b. Based on the non-detection of escaping He for GJ 436 b, we are able to rule out total escape rates higher than 3.4 × 10 10 g s −1 at 99.7% (3σ) confidence.

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“…Observationally, these systems would appear to exhibit a low stellar obliquity, while providing no evidence of additional closein planets. A possible hallmark of such 'violently aligned' systems would be high eccentricity, despite low inclination, such as K2-25b (Gaidos et al 2020;Stefansson et al 2020). Moreover, eccentricities of single-transiting planets appear higher than those of multis (Xie et al 2016;Van Eylen et al 2019), which indicates a violent history.…”

Section: Instability and A Mixed Populationmentioning

confidence: 99%

The distribution of mutual inclinations arising from the stellar quadrupole moment

Schultz

Spalding

Batygin

2021

Monthly Notices of the Royal Astronomical Society

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A large proportion of transiting planetary systems appear to possess only a single planet as opposed to multiple transiting planets. This excess of singles is indicative of significant mutual inclinations existing within a large number of planetary systems, but the origin of these misalignments is unclear. Moreover, recent observational characterization reveals that mutual inclinations tend to increase with proximity to the host star. These trends are both consistent with the dynamical influence of a strong quadrupolar potential arising from the host star during its early phase of rapid rotation, coupled with a non-zero stellar obliquity. Here, we simulate a population of planetary systems subject to the secular perturbation arising from a tilted, oblate host star as it contracts and spins down subsequent to planet formation. We demonstrate that this mechanism can reproduce the general increase in planet-planet mutual inclinations with proximity to the host star, and delineate a parameter space wherein the host star can drive dynamical instabilities. We suggest that approximately 5-10% of low-mass Kepler systems are susceptible to this instability mechanism, suggesting that a significant number of single-transiting planets may truly be intrinsically single. We also report a novel connection between instability and stellar obliquity reduction and make predictions that can be tested within upcoming TESS observations.

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Zodiacal exoplanets in time – XI. The orbit and radiation environment of the young M dwarf-hosted planet K2-25b

Cited by 28 publications

References 41 publications

The Habitable Zone Planet Finder Reveals a High Mass and Low Obliquity for the Young Neptune K2-25b

The Habitable Zone Planet Finder Reveals a High Mass and Low Obliquity for the Young Neptune K2-25b

p-winds: An open-source Python code to model planetary outflows and upper atmospheres

The distribution of mutual inclinations arising from the stellar quadrupole moment

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