| 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. |
- Psaridi, A., et al.
(författare)
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Discovery of two warm mini-Neptunes with contrasting densities orbiting the young K3V star TOI-815
- 2024
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 685
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Tidskriftsartikel (refereegranskat)abstract
- We present the discovery and characterization of two warm mini-Neptunes transiting the K3V star TOI-815 in a K–M binary system. Analysis of its spectra and rotation period reveal the star to be young, with an age of 200+−400200 Myr. TOI-815b has a 11.2-day period and a radius of 2.94 ± 0.05 R+ with transits observed by TESS, CHEOPS, ASTEP, and LCOGT. The outer planet, TOI-815c, has a radius of 2.62 ± 0.10 R+, based on observations of three nonconsecutive transits with TESS; targeted CHEOPS photometry and radial velocity follow-up with ESPRESSO were required to confirm the 35-day period. ESPRESSO confirmed the planetary nature of both planets and measured masses of 7.6 ± 1.5 M+ (ρP = 1.64+−003331 g cm−3) and 23.5 ± 2.4 M+ (ρP = 7.2+−1110 g cm−3), respectively. Thus, the planets have very different masses, which is unusual for compact multi-planet systems. Moreover, our statistical analysis of mini-Neptunes orbiting FGK stars suggests that weakly irradiated planets tend to have higher bulk densities compared to those undergoing strong irradiation. This could be ascribed to their cooler atmospheres, which are more compressed and denser. Internal structure modeling of TOI-815b suggests it likely has a H-He atmosphere that constitutes a few percent of the total planet mass, or higher if the planet is assumed to have no water. In contrast, the measured mass and radius of TOI-815c can be explained without invoking any atmosphere, challenging planetary formation theories. Finally, we infer from our measurements that the star is viewed close to pole-on, which implies a spin-orbit misalignment at the 3σ level. This emphasizes the peculiarity of the system’s orbital architecture, and probably hints at an eventful dynamical history.
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| 3. |
- Tuson, A., et al.
(författare)
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TESS and CHEOPS discover two warm sub-Neptunes transiting the bright K-dwarf HD 15906
- 2023
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Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 523:2, s. 3090-3118
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Tidskriftsartikel (refereegranskat)abstract
- We report the discovery of two warm sub-Neptunes transiting the bright (G = 9.5 mag) K-dwarf HD 15906 (TOI 461, TIC 4646810). This star was observed by the Transiting Exoplanet Survey Satellite (TESS) in sectors 4 and 31, revealing two small transiting planets. The inner planet, HD 15906 b, was detected with an unambiguous period but the outer planet, HD 15906 c, showed only two transits separated by ∼ 734 d, leading to 36 possible values of its period. We performed follow-up observations with the CHaracterising ExOPlanet Satellite (CHEOPS) to confirm the true period of HD 15906 c and improve the radius precision of the two planets. From TESS, CHEOPS, and additional ground-based photometry, we find that HD 15906 b has a radius of 2.24 ± 0.08 R and a period of 10.924709 ± 0.000032 d, whilst HD 15906 c has a radius of 2.93+−000607 R and a period of 21.583298+−00000055000052 d. Assuming zero bond albedo and full day-night heat redistribution, the inner and outer planet have equilibrium temperatures of 668 ± 13 K and 532 ± 10 K, respectively. The HD 15906 system has become one of only six multiplanet systems with two warm (700 K) sub-Neptune sized planets transiting a bright star (G ≤ 10 mag). It is an excellent target for detailed characterization studies to constrain the composition of sub-Neptune planets and test theories of planet formation and evolution.
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| 4. |
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| 5. |
- Faulds, C.B., et al.
(författare)
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Synergy between xylanases from glycoside hydrolase family 10 and family 11 and feruloyl esterase in the release of phenolic acids from cereal arabinoxylan
- 2006
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Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 0175-7598 .- 1432-0614. ; 71:5, s. 622-629
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Tidskriftsartikel (refereegranskat)abstract
- The bioconversion of waste residues (by-products) from cereal processing industries requires the cooperation of enzymes able to degrade xylanolytic and cellulosic material. The type A feruloyl esterase from Aspergillus niger, AnFaeA, works synergistically with (1→4)-β-d-xylopyranosidases (xylanases) to release monomeric and dimeric ferulic acid (FA) from cereal cell wall-derived material. The esterase was more effective with a family 11 xylanase from Trichoderma viride in releasing FA and with a family 10 xylanase from Thermoascus aurantiacus in releasing the 5,5′ form of diferulic acid from arabinoxylan (AX) derived from brewers’ spent grain. The converse was found for the release of the phenolic acids from wheat bran-derived AXs. This may be indicative of compositional differences in AXs in cereals.
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| 6. |
- Kochukhov, Oleg, et al.
(författare)
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A search for very low amplitude magnetoacoustic pulsations with HARPS
- 2008
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Ingår i: Contributions of the Astronomical Observatory Skalnate Pleso. - 1335-1842. ; 38:2, s. 423-424
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Tidskriftsartikel (refereegranskat)abstract
- We have obtained time-resolved spectroscopic observations for a sample of 10 cool Ap stars using the ultra-stable spectrograph HARPS at the ESO 3.6-m telescope. The aim of our study was to search for low-amplitude oscillations in Ap stars with no or inconclusive evidence of pulsational variability. Here we report initial results of our investigation. We confirm the presence of approximate to 16-min period pulsations in beta CrB (HD 137909) and demonstrate multi-periodic character of oscillations in this star. Furthermore, we discovered very low amplitude 9-min pulsations in HD 75445 - an object spectroscopically very similar to known roAp stars.
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| 7. |
- Kochukhov, O., et al.
(författare)
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Discovery of very low amplitude 9-minute multiperiodic pulsations in the magnetic Ap star HD75445
- 2009
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 493:3, s. L45-L48
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Tidskriftsartikel (refereegranskat)abstract
- We present our discovery of pulsational radial-velocity variations in the cool Ap star HD75445, an object spectroscopically similar to the bright, rapidly-oscillating Ap (roAp) star gamma Equ. Based on high-resolution time-series spectroscopy obtained with the HARPS spectrometer at the European Southern Observatory 3.6-m telescope, we detected oscillations in Nd II and Nd III lines with a period close to 9 min and amplitudes of 20-30 m s(-1). Substantial variation in the pulsational amplitude during our 3.8 h observing run reveals the presence of at least three excited non-radial modes. The detection of extremely low amplitude pulsations in HD75445 indicates that the roAp excitation mechanism produces variability in the radial velocity amplitude of between a few tens ms(-1) and several km s(-1). This supports the idea that many, if not all, cool Ap stars occupying the roAp instability strip may harbour non-radial pulsations, which currently remain undetected due to their small photometric and radial-velocity amplitudes.
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| 8. |
- Kochukhov, O., et al.
(författare)
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The discovery of high-amplitude, 10.9-minute oscillations in the cool magnetic Ap star HD 115226
- 2008
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 479:2, s. L29-L32
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Tidskriftsartikel (refereegranskat)abstract
- We present the discovery of pulsational variations in the cool magnetic Ap star HD115226 - the first high-amplitude rapidly oscillating Ap (roAp) star discovered with time-series spectroscopy. Using high-resolution spectra obtained with the HARPS instrument at the European Southern Observatory 3.6-m telescope, we detect radial velocity variations with a period of 10.86 min in Pr III, Nd III, Dy III lines, and in the narrow cores of hydrogen lines. Pulsational amplitudes exceed 1 km s(-1) in individual lines of Nd III. The presence of running waves in the stellar atmosphere is inferred from a phase shift between the radial velocity maxima of rare-earth and hydrogen lines. Our abundance analysis demonstrates that HD115226 exhibits a typical roAp spectroscopic signature, notably ionization anomaly of Pr, Nd, and Dy. We discuss the discovery of pulsations in HD115226 in the context of recent spectroscopic studies of roAp stars and point to the existence of a correlation between spectroscopic pulsational amplitude and the stellar rotation rate.
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| 9. |
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| 10. |
- Ryabchikova, T., et al.
(författare)
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Pulsation in the atmosphere of the roAp star HD 24712 : I. Spectroscopic observations and radial velocity measurements
- 2007
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 462:3, s. 1103-1112
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Tidskriftsartikel (refereegranskat)abstract
- Aims.We have investigated the structure of the pulsating atmosphere of one of the best studied rapidly oscillating Ap stars, HD 24712.Methods.For this purpose we analyzed spectra collected during 2001-2004. An extensive data set was obtained in 2004 simultaneously with the photometry of the Canadian MOST mini-satellite. This allows us to connect directly atmospheric dynamics observed as radial velocity variations with light variations seen in photometry. Results.We directly derived for the first time and for different chemical elements, respectively ions, phase shifts between photometric and radial velocity pulsation maxima indicating, as we suggest, different line formation depths in the atmosphere. This allowed us to estimate for the first time the propagation velocity of a pulsation wave in the outer stellar atmosphere of a roAp star to be slightly lower than the sound speed. We confirm large pulsation amplitudes (150-400 m s-1) for REE lines and the H core, while spectral lines of the other elements (Mg, Si, Ca, and Fe-peak elements) have nearly constant velocities. We did not find different pulsation amplitudes and phases for the lines of rare-earth elements before and after the Balmer jump, which supports the hypothesis of REE concentration in the upper atmosphere above the hydrogen line-forming layers. We also discuss radial velocity amplitudes and phases measured for individual spectral lines as tools for a 3D tomography of the atmosphere of HD 24712.
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