| 1. |
- Morales, J. C., et al.
(författare)
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A giant exoplanet orbiting a very-low-mass star challenges planet formation models
- 2019
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 365:6460, s. 1441-1445
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Tidskriftsartikel (refereegranskat)abstract
- Surveys have shown that super-Earth and Neptune-mass exoplanets are more frequent than gas giants around low-mass stars, as predicted by the core accretion theory of planet formation. We report the discovery of a giant planet around the very-low-mass star GJ 3512, as determined by optical and near-infrared radial-velocity observations. The planet has a minimum mass of 0.46 Jupiter masses, very high for such a small host star, and an eccentric 204-day orbit. Dynamical models show that the high eccentricity is most likely due to planet-planet interactions. We use simulations to demonstrate that the GJ 3512 planetary system challenges generally accepted formation theories, and that it puts constraints on the planet accretion and migration rates. Disk instabilities may be more efficient in forming planets than previously thought.
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| 2. |
- Rauer, H., et al.
(författare)
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The PLATO 2.0 mission
- 2014
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Ingår i: Experimental astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 38:1-2, s. 249-330
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Tidskriftsartikel (refereegranskat)abstract
- PLATO 2.0 has recently been selected for ESA's M3 launch opportunity (2022/24). Providing accurate key planet parameters (radius, mass, density and age) in statistical numbers, it addresses fundamental questions such as: How do planetary systems form and evolve? Are there other systems with planets like ours, including potentially habitable planets? The PLATO 2.0 instrument consists of 34 small aperture telescopes (32 with 25 s readout cadence and 2 with 2.5 s cadence) providing a wide field-of-view (2232 deg(2)) and a large photometric magnitude range (4-16 mag). It focuses on bright (4-11 mag) stars in wide fields to detect and characterize planets down to Earth-size by photometric transits, whose masses can then be determined by ground-based radial-velocity follow-up measurements. Asteroseismology will be performed for these bright stars to obtain highly accurate stellar parameters, including masses and ages. The combination of bright targets and asteroseismology results in high accuracy for the bulk planet parameters: 2 %, 4-10 % and 10 % for planet radii, masses and ages, respectively. The planned baseline observing strategy includes two long pointings (2-3 years) to detect and bulk characterize planets reaching into the habitable zone (HZ) of solar-like stars and an additional step-and-stare phase to cover in total about 50 % of the sky. PLATO 2.0 will observe up to 1,000,000 stars and detect and characterize hundreds of small planets, and thousands of planets in the Neptune to gas giant regime out to the HZ. It will therefore provide the first large-scale catalogue of bulk characterized planets with accurate radii, masses, mean densities and ages. This catalogue will include terrestrial planets at intermediate orbital distances, where surface temperatures are moderate. Coverage of this parameter range with statistical numbers of bulk characterized planets is unique to PLATO 2.0. The PLATO 2.0 catalogue allows us to e. g.: - complete our knowledge of planet diversity for low-mass objects, - correlate the planet mean density-orbital distance distribution with predictions from planet formation theories,- constrain the influence of planet migration and scattering on the architecture of multiple systems, and - specify how planet and system parameters change with host star characteristics, such as type, metallicity and age. The catalogue will allow us to study planets and planetary systems at different evolutionary phases. It will further provide a census for small, low-mass planets. This will serve to identify objects which retained their primordial hydrogen atmosphere and in general the typical characteristics of planets in such a low-mass, low-density range. Planets detected by PLATO 2.0 will orbit bright stars and many of them will be targets for future atmosphere spectroscopy exploring their atmospheres. Furthermore, the mission has the potential to detect exomoons, planetary rings, binary and Trojan planets. The planetary science possible with PLATO 2.0 is complemented by its impact on stellar and galactic science via asteroseismology as well as light curves of all kinds of variable stars, together with observations of stellar clusters of different ages. This will allow us to improve stellar models and study stellar activity. A large number of well-known ages from red giant stars will probe the structure and evolution of our Galaxy. Asteroseismic ages of bright stars for different phases of stellar evolution allow calibrating stellar age-rotation relationships. Together with the results of ESA's Gaia mission, the results of PLATO 2.0 will provide a huge legacy to planetary, stellar and galactic science.
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| 3. |
- Mallorquin, M., et al.
(författare)
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TOI-1801 b: A temperate mini-Neptune around a young M0.5 dwarf
- 2023
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 680
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Tidskriftsartikel (refereegranskat)abstract
- We report the discovery, mass, and radius determination of TOI-1801 b, a temperate mini-Neptune around a young M dwarf. TOI-1801 b was observed in TESS sectors 22 and 49, and the alert that this was a TESS planet candidate with a period of 21.3 days went out in April 2020. However, ground-based follow-up observations, including seeing-limited photometry in and outside transit together with precise radial velocity (RV) measurements with CARMENES and HIRES revealed that the true period of the planet is 10.6 days. These observations also allowed us to retrieve a mass of 5.74 +/- 1.46 M-circle plus, which together with a radius of 2.08 +/- 0.12 R-circle plus, means that TOI-1801 b is most probably composed of water and rock, with an upper limit of 2% by mass of H-2 in its atmosphere. The stellar rotation period of 16 days is readily detectable in our RV time series and in the ground-based photometry. We derived a likely age of 600-800 Myr for the parent star TOI-1801, which means that TOI-1801 b is the least massive young mini-Neptune with precise mass and radius determinations. Our results suggest that if TOI-1801 b had a larger atmosphere in the past, it must have been removed by some evolutionary mechanism on timescales shorter than 1 Gyr.
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| 4. |
- Bluhm, P., et al.
(författare)
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Precise mass and radius of a transiting super-Earth planet orbiting the M dwarf TOI-1235: a planet in the radius gap?
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 639
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Tidskriftsartikel (refereegranskat)abstract
- We report the confirmation of a transiting planet around the bright weakly active M0.5 V star TOI-1235 (TYC 4384-1735-1, V ≈ 11.5 mag), whose transit signal was detected in the photometric time series of sectors 14, 20, and 21 of the TESS space mission. We confirm the planetary nature of the transit signal, which has a period of 3.44 d, by using precise RV measurements with the CARMENES, HARPS-N, and iSHELL spectrographs, supplemented by high-resolution imaging and ground-based photometry. A comparison of the properties derived for TOI-1235 b with theoretical models reveals that the planet has a rocky composition, with a bulk density slightly higher than that of Earth. In particular, we measure a mass of Mp = 5.9 ± 0.6 M⊕ and a radius of Rp = 1.69 ± 0.08 R⊕, which together result in a density of ρp = 6.7- 1.1+ 1.3 g cm-3. When compared with other well-characterized exoplanetary systems, the particular combination of planetary radius and mass places our discovery in the radius gap, which is a transition region between rocky planets and planets with significant atmospheric envelopes. A few examples of planets occupying the radius gap are known to date. While the exact location of the radius gap for M dwarfs is still a matter of debate, our results constrain it to be located at around 1.7 R⊕ or larger at the insolation levels received by TOI-1235 b (~60 S⊕). This makes it an extremely interesting object for further studies of planet formation and atmospheric evolution.
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| 5. |
- Goffo, E., et al.
(författare)
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TOI-4438 b: a transiting mini-Neptune amenable to atmospheric characterization
- 2024
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 685
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Tidskriftsartikel (refereegranskat)abstract
- We report the confirmation and mass determination of a mini-Neptune transiting the M3.5 V star TOI-4438 (G 182-34) every 7.44 days. A transit signal was detected with NASA's TESS space mission in the sectors 40, 52, and 53. In order to validate the planet TOI-4438 b and to determine the system properties, we combined TESS data with high-precision radial velocity measurements from the CARMENES spectrograph, spanning almost one year, and ground-based transit photometry. We found that TOI-4438 b has a radius of Rb = 2.52 ± 0.13 R⊕ (5% precision), which together with a mass of Mb = 5.4 ± 1.1 M⊕ (20% precision), results in a bulk density of ρb = 1.85-0.44+0.51 g cm-3 (~28% precision), aligning the discovery with a volatile-rich planet. Our interior structure retrieval with a pure water envelope yields aminimum water mass fraction of 46% (1σ). TOI-4438 b is a volatile-rich mini-Neptune with likely H/He mixed with molecules, such as water, CO2, and CH4. The primary star has a J-band magnitude of 9.7, and the planet has a high transmission spectroscopy metric (TSM) of 136 ± 13. Taking into account the relatively warm equilibrium temperature of Teq = 435 ± 15 K, and the low activity level of its host star, TOI-4438 b is one of the most promising mini-Neptunes around an M dwarf for transmission spectroscopy studies.
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| 6. |
- Luque, R., et al.
(författare)
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Precise mass determination for the keystone sub-Neptune planet transiting the mid-type M dwarf G 9-40
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 666
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Tidskriftsartikel (refereegranskat)abstract
- Context. Despite being a prominent subset of the exoplanet population discovered in the past three decades, the nature and provenance of sub-Neptune-sized planets is still one of the open questions in exoplanet science. Aims. For planets orbiting bright stars, precisely measuring the orbital and planet parameters of the system is the best approach to distinguish between competing theories regarding their formation and evolution. Methods. We obtained 69 new radial velocity observations of the mid-M dwarf G 9-40 with the CARMENES instrument to measure for the first time the mass of its transiting sub-Neptune planet, G 9-40 b, discovered in data from the K2 mission. Results. Combined with new observations from the TESS mission during Sectors 44, 45, and 46, we are able to measure the radius of the planet to an uncertainty of 3.4% (R-b = 1.900 +/- 0.065 R-circle plus) and determine its mass with a precision of 16% (M-b = 4.00 +/- 0.63 M-circle plus). The resulting bulk density of the planet is inconsistent with a terrestrial composition and suggests the presence of either a water-rich core or a significant hydrogen-rich envelope. Conclusions. G 9-40 b is referred to as a keystone planet due to its location in period-radius space within the radius valley. Several theories offer explanations for the origin and properties of this population and this planet is a valuable target for testing the dependence of those models on stellar host mass. By virtue of its brightness and small size of the host, it joins L 98-59 d as one of the two best warm (T-eq similar to 400 K) sub-Neptunes for atmospheric characterization with JWST, which will probe cloud formation in sub-Neptune-sized planets and break the degeneracies of internal composition models.
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| 7. |
- Fiorina, B., et al.
(författare)
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Challenging modeling strategies for LES of non-adiabatic turbulent stratified combustion
- 2015
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180 .- 1556-2921. ; 162:11, s. 4264-4282
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Tidskriftsartikel (refereegranskat)abstract
- Five different low-Mach large eddy simulations are compared to the turbulent stratified flame experiments conducted at the Technical University of Darmstadt (TUD). The simulations were contributed by TUD, the Institute for Combustion Technology (ITV) at Aachen, Lund University (LUND), the EM2C laboratory at Ecole Centrale Paris, and the University of Duisburg-Essen (UDE). Combustion is modeled by a premixed flamelet tabulation with local flame thickening (TUD), a premixed flamelet progress variable approach coupled to a level set method (ITV), a 4-steps mechanism combined with implicit LES (LUND), the F-TACLES model that is based on filtered premixed flamelet tabulation (EM2C), and a flame surface density approach (UDE). An extensive comparison of simulation and experimental data is presented for the first two moments of velocity, temperature, mixture fraction, and major species mass fractions. The importance of heat-losses was assessed by comparing simulations for adiabatic and isothermal boundary conditions at the burner walls. The adiabatic computations predict a flame anchored on the burner lip, while the non-adiabatic simulations show a flame lift-off of one half pilot diameter and a better agreement with experimental evidence for temperature and species concentrations. Most simulations agree on the mean flame brush position, but it is evident that subgrid turbulence must be considered to achieve the correct turbulent flame speed. Qualitative comparisons of instantaneous snapshots of the flame show differences in the size of the resolved flame wrinkling patterns. These differences are (a) caused by the influence of the LES combustion model on the flame dynamics and (b) by the different simulation strategies in terms of grid, inlet condition and numerics. The simulations were conducted with approaches optimized for different objectives, for example low computational cost, or in another case, short turn around. (C) 2015 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 8. |
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| 9. |
- Kuzuhara, Masayuki, et al.
(författare)
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Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Transmission Spectroscopy
- 2024
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Ingår i: Astrophysical Journal Letters. - 2041-8213 .- 2041-8205. ; 969:1
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Tidskriftsartikel (refereegranskat)abstract
- Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (P(or)b) of 12.76 days. The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous P-orb from TESS data. We confirmed the transit signal and P-orb using ground-based photometry with MuSCAT2 and MuSCAT3, and validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host star is inactive, with an X-ray-to-bolometric luminosity ratio of log L-X/L-bol approximate to - 5.7. Joint analysis of the light curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 +/- 0.05 R-circle plus, a 3 sigma mass upper limit of 3.9M(circle plus), and an equilibrium temperature of 315 +/- 6 K assuming zero albedo. The transmission spectroscopy metric (TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
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| 10. |
- Nauert, A., et al.
(författare)
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Experimental analysis of flashback in lean premixed swirling flames: conditions close to flashback
- 2007
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Ingår i: Experiments in Fluids. - : Springer Science and Business Media LLC. - 1432-1114 .- 0723-4864. ; 43:1, s. 89-100
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Tidskriftsartikel (refereegranskat)abstract
- Swirling lean premixed flames are of practical relevance due to their potential for low nitric oxide (NOx) emissions. Unfortunately, these flames have various drawbacks. One critical attribute is the possibility for flashback of the reacting flow into the nozzle. Advanced numerical simulations should be able in the future to predict the transition from stable flames to flashback. For a better understanding of the process itself and for validation of numerical simulation a well-documented generic benchmark experiment is needed. This study presents a burner configuration that has already been studied extensively in the past. By minor geometrical adaptations, and via the possibility to vary the swirl intensity in a controlled way, the transition from stable flames to flashback is now accessible to detailed characterisation using advanced laser diagnostics. In a first part of this study the different states of the flame were classified. In the second part, both a stable and a precessing flame very close to flash back were compared in terms of flow and scalar field. The variation of the swirl intensity on the flame is discussed. Because the flame is strongly influenced by its inflow conditions additional velocity measurements inside the nozzle were carried out. This is of special importance for subsequent numerical simulations to match the experimental conditions. The quantitative investigation of the flame during flashback is subjected to consecutive experiments where planar laser diagnostics at high repetition rates will be exploited.
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| 11. |
- Nogenmyr, Karl-Johan, et al.
(författare)
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Large Eddy Simulation and Experiments of Stratified Lean Premixed Methane/Air Turbulent Flames
- 2007
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 31:1, s. 1467-1475
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a joint large eddy simulation and laser diagnostic investigation of premixed turbulent low swirl flames. A lean premixed methane/air mixture, of the equivalence ratio 0.60-0.66, is injected from a 50 mm diameter low swirl burner to a low speed co-flowing air at room temperature and pressure. The level-set G-equation is employed to simulate the inner layer flame front. Flamelet chemistry is used to determine the flame properties in the reactive zones. Mixing and heat transfer in the post-flame zone down-stream are modeled using transport equations. In addition to large eddy simulation, simultaneous 2-D laser induced fluorescence of OH and 2-D particle image velocimetry are used to characterize the basic flame structure. Laser Doppler velocimetry is employed to further analyze the flow velocity along the central axis above the burner, and 2-D filtered Rayleigh scattering is used to measure the temperature field in the lower part of the flame. A bowl-shaped, highly wrinkled turbulent flame is stabilized at a position about one-half diameter above the burner. The flame consists of two distinct parts; around the burner axis, a premixed flame with uniform mixture fraction is stabilized in the low speed flow region induced by the inflow swirl; off the axis of the burner, a stratified lean premixed flame is found in the shear layer of the flow field. Flame holes (local extinction) owing to overly lean mixtures are observed in the off-axis lean stratified part of the flame. A unified level-set G-equation is developed to model the flame holes. The basic flow and flame structure from the model simulations are compared to the laser diagnostic measurements; the height of flame stabilization (lift-off height), the mean temperature profile, and the mean axial and radial velocity components together with rms velocity components are in fairly good agreement with measurement data. © 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 12. |
- Bruebach, J., et al.
(författare)
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Determination of surface normal temperature gradients using thermographic phosphors and filtered Rayleigh scattering
- 2006
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 84:3, s. 537-541
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Tidskriftsartikel (refereegranskat)abstract
- Wall temperature as well as the temperature distribution within or close-by the boundary layer of an electrically heated axisymmetric jet impinging on a flat plate were monitored to deduce wall-normal temperature gradients. The radial surface temperature profile of the plate was determined by coating it with thermographic phosphors (TPs), materials whose phosphorescence decay time is dependent on their temperature. The TP was excited electronically by a frequency-tripled Nd:YAG laser (355 nm) and the temporal decay of the phosphorescence intensity was measured zero-dimensionally by a photomultiplier tube. In this case the 659-nm emission line of Mg3F2GeO4:Mn was monitored. The non-intrusive measurement of gas temperatures near the surface was performed two-dimensionally by filtered Rayleigh scattering (FRS). A tunable frequency-tripled single-longitudinal-mode alexandrite laser beam at 254 nm was formed into a light sheet pointing parallel to the surface. The scattered light was imaged through a very narrow linewidth atomic mercury filter onto an intensified charged coupled device (ICCD). The elastic stray light from surfaces was strongly suppressed, whereas Doppler-broadened light was detected. Thermographic phosphors proved to be reliable for the measurement of surface temperatures. Dependent on the specific experimental conditions, problems appeared with signals interfering with the FRS radiation close-by the surface. Results and challenges of this approach are discussed.
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| 13. |
- Giesers, B., et al.
(författare)
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A stellar census in globular clusters with MUSE: Binaries in NGC 3201
- 2019
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 632
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Tidskriftsartikel (refereegranskat)abstract
- We utilise multi-epoch MUSE spectroscopy to study binary stars in the core of the Galactic globular cluster NGC 3201. Our sample consists of 3553 stars with 54 883 spectra in total comprising 3200 main-sequence stars up to 4 magnitudes below the turn-off. Each star in our sample has between 3 and 63 (with a median of 14) reliable radial velocity measurements within five years of observations. We introduce a statistical method to determine the probability of a star showing radial velocity variations based on the whole inhomogeneous radial velocity sample. Using HST photometry and an advanced dynamical MOCCA simulation of this specific cluster we overcome observational biases that previous spectroscopic studies had to deal with. This allows us to infer a binary frequency in the MUSE field of view and enables us to deduce the underlying true binary frequency of (6.75 ± 0.72)% in NGC 3201. The comparison of the MUSE observations with the MOCCA simulation suggests a large portion of primordial binaries. We can also confirm a radial increase in the binary fraction towards the cluster centre due to mass segregation. We discovered that in the core of NGC 3201 at least (57.5 ± 7.9)% of blue straggler stars are in a binary system. For the first time in a study of globular clusters, we were able to fit Keplerian orbits to a significant sample of 95 binaries. We present the binary system properties of eleven blue straggler stars and the connection to SX Phoenicis-type stars. We show evidence that two blue straggler formation scenarios, the mass transfer in binary (or triple) star systems and the coalescence due to binary-binary interactions, are present in our data. We also describe the binary and spectroscopic properties of four sub-subgiant (or red straggler) stars. Furthermore, we discovered two new black hole candidates with minimum masses (M sin i) of (7.68 ± 0.50) M⊙, (4.4 ± 2.8) M⊙, and refine the minimum mass estimate on the already published black hole to (4.53 ± 0.21) M⊙. These black holes are consistent with an extensive black hole subsystem hosted by NGC 3201.
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| 14. |
- Kaminski, Clemens, et al.
(författare)
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Flame growth and wrinkling in a turbulent flow
- 2000
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Ingår i: Applied physics. B, Lasers and optics (Print). - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 71:5, s. 711-716
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Tidskriftsartikel (refereegranskat)abstract
- High-speed planar laser-induced fluorescence (PLIF) and 3-D large eddy simulations (LES) are used to study turbulent flame kernel growth, wrinkling and the formation of separated flame pockets in methane/air mixtures. Turbulence was effected by a set of rotary fans situated in a cylindrical enclosure. Flame wrinkling was followed on sequential 2-D OH images captured at kHz repetition rates. Under stoichiometric conditions and low turbulence levels the flame kernel remains singly connected and close to spherical in shape. By increasing turbulence or reducing the stoichiometry of the mixture the formation of separated pockets could be observed and studied. The mechanisms behind these phenomena are investigated qualitatively by LES of a level-set G-equation describing the flame surface propagation in turbulent flows.
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| 15. |
- Walewski, Joachim, et al.
(författare)
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Polarization spectroscopy applied to the detection of trace constituents in sooting combustion
- 2004
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 58:2, s. 238-242
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Tidskriftsartikel (refereegranskat)abstract
- The potential of polarization spectroscopy for the detection of trace constituents in sooting combustion was investigated. It was demonstrated that the directionality of the polarization spectroscopy signal can be exploited to efficiently suppress incoherent interferences, e.g., Rayleigh scattering at soot particles. We also show how polarization spectroscopy compares with laser-induced fluorescence in this type of environment by applying both techniques to atmospheric-pressure, premixed propane/oxygen flames. The acquired signals were spatially resolved along the centerline of the flame, and measurements were conducted at several heights above the burner head and for medium to very high fuel-to-oxidizer ratios. Through our work we found that polarization spectroscopy can be applied even in the presence of large soot fractions. For most conditions, where laser-induced fluorescence suffered from interferences like elastic scattering, spatially filtered polarization spectroscopy signals were virtually background-free, and only for high soot loads did a noticeable background on the latter signal appear. This background likely stems from Mie scattering at very large soot particles.
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