| 1. |
- Leleu, A., et al.
(författare)
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Six transiting planets and a chain of Laplace resonances in TOI-178
- 2021
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 649
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Tidskriftsartikel (refereegranskat)abstract
- Determining the architecture of multi-planetary systems is one of the cornerstones of understanding planet formation and evolution. Resonant systems are especially important as the fragility of their orbital configuration ensures that no significant scattering or collisional event has taken place since the earliest formation phase when the parent protoplanetary disc was still present. In this context, TOI-178 has been the subject of particular attention since the first TESS observations hinted at the possible presence of a near 2:3:3 resonant chain. Here we report the results of observations from CHEOPS, ESPRESSO, NGTS, and SPECULOOS with the aim of deciphering the peculiar orbital architecture of the system. We show that TOI-178 harbours at least six planets in the super-Earth to mini-Neptune regimes, with radii ranging from 1.152 to 2.87 Earth radii and periods of 1.91, 3.24, 6.56, 9.96, 15.23, and 20.71 days. All planets but the innermost one form a 2:4:6:9:12 chain of Laplace resonances, and the planetary densities show important variations from planet to planet, jumping from 1.02 to 0.177 times the Earth's density between planets c and d. Using Bayesian interior structure retrieval models, we show that the amount of gas in the planets does not vary in a monotonous way, contrary to what one would expect from simple formation and evolution models and unlike other known systems in a chain of Laplace resonances. The brightness of TOI-178 (H = 8.76 mag, J = 9.37 mag, V = 11.95 mag) allows for a precise characterisation of its orbital architecture as well as of the physical nature of the six presently known transiting planets it harbours. The peculiar orbital configuration and the diversity in average density among the planets in the system will enable the study of interior planetary structures and atmospheric evolution, providing important clues on the formation of super-Earths and mini-Neptunes. -0.070 -0.13 -0.23 -0.061 +0.073 +0.14 +0.28 +0.055
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| 2. |
- Nielsen, L. D., et al.
(författare)
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Mass determinations of the three mini-Neptunes transiting TOI-125
- 2020
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 492:4, s. 5399-5412
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Tidskriftsartikel (refereegranskat)abstract
- The Transiting Exoplanet Survey Satellite, TESS, is currently carrying out an all-sky search for small planets transiting bright stars. In the first year of the TESS survey, a steady progress was made in achieving the mission's primary science goal of establishing bulk densities for 50 planets smaller than Neptune. During that year, the TESS's observations were focused on the southern ecliptic hemisphere, resulting in the discovery of three mini-Neptunes orbiting the star T01-125, a V = 11,0 KO dwarf. We present intensive HARPS radial velocity observations, yielding precise mass measurements for TO1-125b, TOI-125c, and TOI-125d. TOI-125b has an orbital period of 4,65 d, a radius of 2,726 + 0,075 RE, a mass of 9,50 0,88 ME, and is near the 2:1 mean motion resonance with TOI-125c at 9.15 d. TOI-125c has a similar radius of 2,759 0.10 RE and a mass of 6,63 + 0,99 ME, being the puffiest of the three planets. T01-125d has an orbital period of 19,98 d and a radius of 2.93 + 0,17 RE and mass 13,6 1,2 ME, For T01-125b and d, we find unusual high eccentricities of 0.19 0.04 and 0.17+(c):(!,(, respectively. Our analysis also provides upper mass limits for the two low-SNR planet candidates in the system; for T01-125.04 (Rp = 1.36 RE, P = 0.53 d), we find a 2a upper mass limit of 1.6 ME, whereas T01-125.05 (RP = 4.2-'2E44 RE, P = 13.28 d) is unlikely a viable planet candidate with an upper mass limit of 2.7 ME. We discuss the internal structure of the three confirmed planets, as well as dynamical stability and system architecture for this intriguing exoplanet system.
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| 3. |
- Lee, Justin H., et al.
(författare)
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Application of Cold and Hot Plasma Composition Measurements to Investigate Impacts on Dusk-Side Electromagnetic Ion Cyclotron Waves
- 2021
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 126:1
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Tidskriftsartikel (refereegranskat)abstract
- An extended interval of perturbed magnetospheric conditions in November 2016 supported increased convection and sunward transport of plasmaspheric material. During this period of time the Magnetospheric Multiscale satellites, with their apogees along Earth's dusk-side outer magnetosphere, encountered several cold plasma density structures at the same time as plasma bulk flows capable of accelerating hidden cold plasma occurred. Investigating the charged particle and fields data during two subintervals showed that the satellites made direct measurements of cold plasmaspheric ions embedded within multicomponent hot plasmas as well as electromagnetic emissions consistent with electromagnetic ion cyclotron (EMIC) waves. The complex in situ ion composition measurements were applied to linear wave modeling to interpret the impacts of cold and hot ion species on wave growth and band structure. Although the waves for both intervals were predicted to have peak growth rate below omega(He+), substantial differences were observed among all other dispersive properties. The modeling also showed EMIC waves generated in the presence of heavy ions had growth rates and unstable wave numbers always smaller than predicted for a pure proton-electron plasma. The results provide implications for future investigation of EMIC wave generation with and without direct measurements of the cold and hot plasma composition as well as of subsequent wave-particle interactions.
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| 4. |
- Persson, Carina, 1964, et al.
(författare)
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TOI-2196 b: Rare planet in the hot Neptune desert transiting a G-type star
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 666
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Tidskriftsartikel (refereegranskat)abstract
- The hot Neptune desert is a region hosting a small number of short-period Neptunes in the radius-instellation diagram. Highly irradiated planets are usually either small (R less than or similar to 2 R-circle plus) and rocky or they are gas giants with radii of greater than or similar to 1 R-J. Here, we report on the intermediate-sized planet TOI-2196 b (TIC 372172128.01) on a 1.2 day orbit around a G-type star (V = 12.0, [Fe/H] = 0.14 dex) discovered by the Transiting Exoplanet Survey Satellite in sector 27. We collected 41 radial velocity measurements with the HARPS spectrograph to confirm the planetary nature of the transit signal and to determine the mass. The radius of TOI-2196 b is 3.51 +/- 0.15 R-circle plus, which, combined with the mass of 26.0 +/- 1.3 M-circle plus, results in a bulk density of 3.31(-0.43)(+0.51) g cm(-3). Hence, the radius implies that this planet is a sub-Neptune, although the density is twice than that of Neptune. A significant trend in the HARPS radial velocity measurements points to the presence of a distant companion with a lower limit on the period and mass of 220 days and 0.65 M-J, respectively, assuming zero eccentricity. The short period of planet b implies a high equilibrium temperature of 1860 +/- 20 K, for zero albedo and isotropic emission. This places the planet in the hot Neptune desert, joining a group of very few planets in this parameter space discovered in recent years. These planets suggest that the hot Neptune desert may be divided in two parts for planets with equilibrium temperatures of greater than or similar to 1800 K: a hot sub-Neptune desert devoid of planets with radii of approximate to 1.8-3 R-circle plus and a sub-Jovian desert for radii of approximate to 5-12 R-circle plus. More planets in this parameter space are needed to further investigate this finding. Planetary interior structure models of TOI-2196 b are consistent with a H/He atmosphere mass fraction between 0.4% and 3%, with a mean value of 0.7% on top of a rocky interior. We estimated the amount of mass this planet might have lost at a young age and we find that while the mass loss could have been significant, the planet had not changed in terms of character: it was born as a small volatile-rich planet and it remains one at present.
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| 5. |
- Toledo-Redondo, S., et al.
(författare)
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Kinetic Interaction of Cold and Hot Protons With an Oblique EMIC Wave Near the Dayside Reconnecting Magnetopause
- 2021
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 48:8
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Tidskriftsartikel (refereegranskat)abstract
- We report observations of the ion dynamics inside an Alfven branch wave that propagates near the reconnecting dayside magnetopause. The measured frequency, wave normal angle and polarization are consistent with the predictions of a dispersion solver. The magnetospheric plasma contains hot protons (keV), cold protons (eV), plus some heavy ions. While the cold protons follow the magnetic field fluctuations and remain frozen-in, the hot protons are at the limit of magnetization. The cold protons exchange energy back and forth, adiabatically, with the wave fields. The cold proton velocity fluctuations contribute to balance the Hall term fluctuations in Ohm's law, and the wave E field has small ellipticity and right-handed polarization. The dispersion solver indicates that increasing the cold proton density facilitates propagation and amplification of these waves at oblique angles, as for the observed wave. Plain Language Summary The Earth's magnetosphere is a very dilute cloud of charged particles that are trapped in the Earth's magnetic field. This cloud is surrounded by the solar wind, another very dilute gas that flows supersonically throughout the solar system. These two plasmas can couple to each other via magnetic reconnection, a fundamental plasma process that occurs at the dayside region of the interface between the two plasmas. When reconnection occurs, large amounts of energy and particles enter the magnetosphere, driving the near Earth space dynamics and generating, for instance, aurorae. The magnetospheric plasma sources are the solar wind and the Earth's ionosphere. Multiple plasma populations can be found inside the Earth's magnetosphere, depending on the plasma origin and its time history, as well as the magnetospheric forcing of the solar wind. In this study, we show how the presence of multiple particle populations at the interface between the solar wind and the magnetosphere modifies the properties of the waves that propagate there. Waves are known to play a fundamental role in converting energy and heating these very dilute charged gas clouds.
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| 6. |
- Bathen, M. E., et al.
(författare)
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Influence of carbon cap on self-diffusion in silicon carbide
- 2020
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Ingår i: Crystals. - : MDPI AG. - 2073-4352. ; 10:9, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- Self-diffusion of carbon (12C and13C) and silicon (28Si and30Si) in 4H silicon carbide has been investigated by utilizing a structure containing an isotope purified 4H-28Si12C epitaxial layer grown on an n-type (0001) 4H-SiC substrate, and finally covered by a carbon capping layer (C-cap). The13C and30Si isotope profiles were monitored using secondary ion mass spectrometry (SIMS) following successive heat treatments performed at 2300–2450◦C in Ar atmosphere using an inductively heated furnace. The30Si profiles show little redistribution within the studied temperature range, with the extracted diffusion lengths for Si being within the error bar for surface roughening during annealing, as determined by profilometer measurements. On the other hand, a significant diffusion of13C was observed into the isotope purified layer from both the substrate and the C-cap. A diffusivity of D = 8.3 × 106 e−10.4/kBT cm2/s for13C was extracted, in contrast to previous findings that yielded lower both pre-factors and activation energies for C self-diffusion in SiC. The discrepancy between the present measurements and previous theoretical and experimental works is ascribed to the presence of the C-cap, which is responsible for continuous injection of C interstitials during annealing, and thereby suppressing the vacancy mediated diffusion.
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| 7. |
- Diaz, Matias R., et al.
(författare)
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TOI-132 b: A short-period planet in the Neptune desert transiting a V=11.3 G-type star
- 2020
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 493:1, s. 973-985
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Tidskriftsartikel (refereegranskat)abstract
- The Neptune desert is a feature seen in the radius-period plane, whereby a notable dearth of short period, Neptune-like planets is found. Here, we report the Transiting Exoplanet Survey Satellite (TESS) discovery of a new short-period planet in the Neptune desert, orbiting the G-type dwarf TYC 8003-1117-1 (TOI-132). TESS photometry shows transit-like dips at the level of similar to 1400 ppm occurring every similar to 2.11 d. High-precision radial velocity follow-up with High Accuracy Radial Velocity Planet Searcher confirmed the planetary nature of the transit signal and provided a semi-amplitude radial velocity variation of 11.38(-0.85)(+0.84) m s(-1), which, when combined with the stellar mass of 0.97 +/- 0.06 M-circle dot, provides a planetary mass of 22.40(-1.92)(+1.90) M-circle plus. Modelling the TESS light curve returns a planet radius of 3.42(-0.14)(+0.13) R-circle plus , and therefore the planet bulk density is found to be 3.08(-0.46)(+0.44) g cm(-3). Planet structure models suggest that the bulk of the planet mass is in the form of a rocky core, with an atmospheric mass fraction of 4.3(-2.3)(+1.2) percent. TOI-132 b is a TESS Level 1 Science Requirement candidate, and therefore priority follow-up will allow the search for additional planets in the system, whilst helping to constrain low-mass planet formation and evolution models, particularly valuable for better understanding of the Neptune desert.
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| 8. |
- Gogova, D., et al.
(författare)
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High crystalline quality homoepitaxial Si-doped β-Ga2O3(010) layers with reduced structural anisotropy grown by hot-wall MOCVD
- 2024
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Ingår i: Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films. - 0734-2101. ; 42:2
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Tidskriftsartikel (refereegranskat)abstract
- A new growth approach, based on the hot-wall metalorganic chemical vapor deposition concept, is developed for high-quality homoepitaxial growth of Si-doped single-crystalline β -Ga 2 O 3 layers on (010)-oriented native substrates. Substrate annealing in argon atmosphere for 1 min at temperatures below 600 ° C is proposed for the formation of epi-ready surfaces as a cost-effective alternative to the traditionally employed annealing process in oxygen-containing atmosphere with a time duration of 1 h at about 1000 ° C. It is shown that the on-axis rocking curve widths exhibit anisotropic dependence on the azimuth angle with minima for in-plane direction parallel to the [001] and maximum for the [100] for both substrate and layer. The homoepitaxial layers are demonstrated to have excellent structural properties with a β -Ga 2 O 3 (020) rocking curve full-widths at half-maximum as low as 11 arc sec, which is lower than the corresponding one for the substrates (19 arc sec), even for highly Si-doped (low 10 19 cm − 3 range) layers. Furthermore, the structural anisotropy in the layer is substantially reduced with respect to the substrate. Very smooth surface morphology of the epilayers with a root mean square roughness value of 0.6 nm over a 5 × 5 μ m 2 area is achieved along with a high electron mobility of 69 cm 2 V − 1 s − 1 at a free carrier concentration n = 1.9 × 10 19 cm − 3 . These values compare well with state-of-the-art parameters reported in the literature for β -Ga 2 O 3 (010) homoepitaxial layers with respective Si doping levels. Thermal conductivity of 17.4 W m − 1 K − 1 is determined along the [010] direction for the homoepitaxial layers at 300 K, which approaches the respective value of bulk crystal (20.6 W m − 1 K − 1 ). This result is explained by a weak boundary effect and a low dislocation density in the homoepitaxial layers.
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| 9. |
- Grini, S., et al.
(författare)
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Dynamic Impurity Redistributions in Kesterite Absorbers
- 2020
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Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951.
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Tidskriftsartikel (refereegranskat)abstract
- Cu2ZnSn(S,Se)4 is a promising nontoxic earth-abundant solar cell absorber. To optimize the thin films for solar cell device performance, postdeposition treatments at temperatures below the crystallization temperature are normally performed, which alter the surface and bulk properties. The polycrystalline thin films contain relatively high concentrations of impurities, such as sodium, oxygen and hydrogen. During the treatments, these impurities migrate and likely agglomerate at lattice defects or interfaces. Herein, impurity redistribution after air annealing for temperatures up to 200 °C and short heavy water treatments are studied. In addition, nonuniformities of the sodium distribution on a nanometer and micrometer scale are characterized by atom probe tomography and secondary ion mass spectrometry, respectively. Sodium and oxygen correlate to a greater extent after heat treatments, supporting strong binding between the two impurities. Redistributions of these impurities occur even at room temperature over longer time periods. Heavy water treatments confirm out-diffusion of sodium with more incorporation of oxygen and hydrogen. It is observed that the increased hydrogen content does not originate from the heavy water. The existence of an “ice-like” layer on top of the Cu2ZnSnS4 layer is proposed.
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| 10. |
- Li, Yu-Xuan, et al.
(författare)
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Quantification of Cold-Ion Beams in a Magnetic Reconnection Jet
- 2021
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Ingår i: Frontiers in Astronomy and Space Sciences. - : Frontiers Media S.A.. - 2296-987X. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Cold (few eV) ions of ionospheric origin are widely observed in the lobe region of Earth's magnetotail and can enter the ion jet region after magnetic reconnection is triggered in the magnetotail. Here, we investigate a magnetotail crossing with cold ions in one tailward and two earthward ion jets observed by the Magnetospheric Multiscale (MMS) constellation of spacecraft. Cold ions co-existing with hot plasma-sheet ions form types of ion velocity distribution functions (VDFs) in the three jets. In one earthward jet, MMS observe cold-ion beams with large velocities parallel to the magnetic fields, and we perform quantitative analysis on the ion VDFs in this jet. The cold ions, together with the hot ions, are reconnection outflow ions and are a minor population in terms of number density inside this jet. The average bulk speed of the cold-ion beams is approximately 38% larger than that of the hot plasma-sheet ions. The cold-ion beams inside the explored jet are about one order of magnitude colder than the hot plasma-sheet ions. These cold-ion beams could be accelerated by the Hall electric field in the cold ion diffusion region and the shrinking magnetic field lines through the Fermi effect.
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