Keywords

The tidal interactions of planets affect the stellar evolutionary status and the constraint of their physical parameters by gyrochronology. In this work, we incorporate the tidal interaction and magnetic braking of the stellar wind into MESA and calculate a large grid of 25,000 models, covering planets with masses of 0.1–13.0 M_J with different orbital distances that orbit late-type stars of different metallicities. We also explore the effect of different stellar initial rotations on the tidal interactions. Our results show that in the case of tidal inward migration, the stellar rotation periods are always lower than that of the star without planet before the planet is engulfed and the difference in the rotation period of its host star always increases with time. After the planet is engulfed, the stellar rotation periods are still lower than that of star without planet, but the difference of periods can be quickly eliminated if the star has a thick convective envelope (smaller mass and larger metallicity), regardless of the mass of the planet and the initial rotation period of the star. In the case of stars with thinner convective envelopes (larger mass and smaller metallicity), the stars will be spun up and remain the faster rotation in a long time. Meanwhile, the planet is easily swallowed and the period differences are large if the initial rotation period of its host star is higher. Finally, we also study the evolution of WASP-19 and estimate the range of tidal quality parameter ${Q}_{* }^{{\prime} }=(4.6\pm 0.9)\times {10}^{6}$ and the initial semimajor axis as (0.035 ± 0.004) au.

Photospheric C, N, and O abundances of 118 solar-analog stars were determined by applying the synthetic-fitting analysis to their spectra in the blue or near-UV region comprising lines of CH, NH, and OH molecules, with an aim of clarifying the behaviors of these abundances in comparison with [Fe/H]. It turned out that, in the range of −0.6 ≲ [Fe/H] ≲ +0.3, [C/Fe] shows a marginally increasing tendency with decreasing [Fe/H] with a slight upturn around [Fe/H] ∼ 0, [N/Fe] tends to somewhat decrease toward lower [Fe/H], and [O/Fe] systematically increases (and thus [C/O] decreases) with a decrease in [Fe/H]. While these results are qualitatively consistent with previous determinations mostly based on atomic lines, the distribution centers of these [C/Fe], [N/Fe], and [O/Fe] at the near-solar metallicity are slightly negative by several hundredths of dex, which is interpreted as due to unusual solar abundances possibly related to the planetary formation of our solar system. However, clear anomalies are not observed in the [C, N, O/Fe] ratios of planet-host stars. Three out of four very Be-deficient stars were found to show anomalous [C/Fe] or [N/Fe] which may be due to mass transfer from the evolved companion, though its relation to the Be depletion mechanism is still unclear.

We consider the impact of electromagnetic induction and ohmic heating on a conducting planetary object that orbits a magnetic star. Power dissipated as heat saps orbital energy. If this heat is trapped by an insulating crust or mantle, interior temperatures increase substantially. We provide a quantitative description of this behavior and discuss the astrophysical scenarios in which it might occur. Magnetic fields around some main-sequence stars and white dwarfs are strong enough to cause the decay of close-in orbits of asteroids and dwarf planets, drawing them through the Roche limit on megayear timescales. We confirm that ohmic heating around neutron stars is driven by the rotation of the stellar magnetic dipole, not orbital dynamics. In any case, heating can raise interior temperatures of asteroids or dwarf planets on close-in orbits to well above liquidus. Hot material escaping to the surface may lead to volcanic ejections that can obscure the host star (as in the light curve of KIC 8462852) and pollute its atmosphere (as observed with metal-rich white dwarfs). We speculate that mixing of a volatile-rich mantle or crust with material from an induction-heated core may lead to an explosion that could destroy the asteroid prior to tidal breakup.

Because of their activity, late-type stars are known to host powerful flares producing intense high-energy radiation on short timescales that may significantly affect the atmosphere of nearby planets. We employ a one-dimensional aeronomic model to study the reaction of the upper atmosphere of the hot Jupiter HD 209458b to the additional high-energy irradiation caused by a stellar flare. Atmospheric absorption of the additional energy produced during a flare leads to local atmospheric heating, accompanied by the formation of two propagating shock waves. We present estimates of the additional atmospheric loss occurring in response to the flare. We find the mass-loss rate at the exobase level to significantly increase (3.8 × 10¹⁰, 8 × 10¹⁰, and 3.5 × 10¹¹ g s⁻¹ for 10, 100, and 1000 times the high-energy flux of the quiet star, respectively) in comparison to that found considering the inactive star (2 × 10¹⁰ g s⁻¹).

We present new observations of four closely spaced near-ultraviolet (NUV) transits of the hot Jupiter-like exoplanet WASP-12b using Hubble Space Telescope (HST)/Cosmic Origins Spectrograph (COS), significantly increasing the phase resolution of the observed NUV light curve relative to previous observations, while minimizing the temporal variation of the system. We observe significant excess NUV absorption during the transit, with mean normalized in-transit fluxes of ${{F}_{{\rm norm}}}\simeq 0.97$, i.e., $\simeq$2–5σ deeper than the optical transit level of $\simeq 0.986$ for a uniform stellar disk (the exact confidence level depending on the normalization method used). We further observe an asymmetric transit shape, such that the post-conjunction fluxes are overall $\simeq$2–3σ higher than pre-conjunction values, and characterized by rapid variations in count rate between the pre-conjunction and out-of-transit levels. We do not find evidence for an early ingress to the NUV transit as suggested by earlier HST observations. However, we show that the NUV count rate observed prior to the optical transit is highly variable, but overall $\simeq$2.2–3.0σ below the post-transit values and comparable in depth to the optical transit, possibly forming a variable region of NUV absorption from at least phase $\phi \simeq 0.83$, limited by the data coverage.

The search for life on planets outside our solar system will use spectroscopic identification of atmospheric biosignatures. The most robust remotely detectable potential biosignature is considered to be the detection of oxygen (O₂) or ozone (O₃) simultaneous to methane (CH₄) at levels indicating fluxes from the planetary surface in excess of those that could be produced abiotically. Here we use an altitude-dependent photochemical model with the enhanced lower boundary conditions necessary to carefully explore abiotic O₂ and O₃ production on lifeless planets with a wide variety of volcanic gas fluxes and stellar energy distributions. On some of these worlds, we predict limited O₂ and O₃ buildup, caused by fast chemical production of these gases. This results in detectable abiotic O₃ and CH₄ features in the UV-visible, but no detectable abiotic O₂ features. Thus, simultaneous detection of O₃ and CH₄ by a UV-visible mission is not a strong biosignature without proper contextual information. Discrimination between biological and abiotic sources of O₂ and O₃ is possible through analysis of the stellar and atmospheric context—particularly redox state and O atom inventory—of the planet in question. Specifically, understanding the spectral characteristics of the star and obtaining a broad wavelength range for planetary spectra should allow more robust identification of false positives for life. This highlights the importance of wide spectral coverage for future exoplanet characterization missions. Specifically, discrimination between true and false positives may require spectral observations that extend into infrared wavelengths and provide contextual information on the planet's atmospheric chemistry.

Near-UV observations of the planet host star WASP-12 uncovered the apparent absence of the normally conspicuous core emission of the Mg ii h and k resonance lines. This anomaly could be due either to (1) a lack of stellar activity, which would be unprecedented for a solar-like star of the imputed age of WASP-12 or (2) extrinsic absorption, from the intervening interstellar medium (ISM) or from material within the WASP-12 system itself, presumably ablated from the extreme hot Jupiter WASP-12 b. HIRES archival spectra of the Ca ii H and K lines of WASP-12 show broad depressions in the line cores, deeper than those of other inactive and similarly distant stars and similar to WASP-12's Mg ii h and k line profiles. We took high-resolution ESPaDOnS and FIES spectra of three early-type stars within 20' of WASP-12 and at similar distances, which show the ISM column is insufficient to produce the broad Ca ii depression observed in WASP-12. The EBHIS H i column density map supports and strengthens this conclusion. Extrinsic absorption by material local to the WASP-12 system is therefore the most likely cause of the line core anomalies. Gas escaping from the heavily irradiated planet could form a stable and thick circumstellar disk/cloud. The anomalously low stellar activity index ($\log R^{{\prime }}_{{\rm HK}}$) of WASP-12 is evidently a direct consequence of the extra core absorption, so similar HK index deficiencies might signal the presence of translucent circumstellar gas around other stars hosting evaporating planets.