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- Van Grootel, V., et al.
(författare)
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A search for transiting planets around hot subdwarfs: I. Methods and performance tests on light curves from Kepler, K2, TESS, and CHEOPS
- 2021
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 650
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Tidskriftsartikel (refereegranskat)abstract
- Context. Hot subdwarfs experienced strong mass loss on the red giant branch (RGB) and are now hot and small He-burning objects. These stars constitute excellent opportunities for addressing the question of the evolution of exoplanetary systems directly after the RGB phase of evolution. Aims. In this project we aim to perform a transit survey in all available light curves of hot subdwarfs from space-based telescopes (Kepler, K2, TESS, and CHEOPS) with our custom-made pipeline SHERLOCK in order to determine the occurrence rate of planets around these stars as a function of orbital period and planetary radius. We also aim to determine whether planets that were previously engulfed in the envelope of their red giant host star can survive, even partially, as a planetary remnant. Methods. For this first paper, we performed injection-and-recovery tests of synthetic transits for a selection of representative Kepler, K2, and TESS light curves to determine which transiting bodies in terms of object radius and orbital period we will be able to detect with our tools. We also provide estimates for CHEOPS data, which we analyzed with the pycheops package. Results. Transiting objects with a radius ≤ 1.0 R⊕ can be detected in most of the Kepler, K2, and CHEOPS targets for the shortest orbital periods (1 d and shorter), reaching values as low as ∼0.3 R⊕ in the best cases. Sub-Earth-sized bodies are only reached for the brightest TESS targets and for those that were observed in a significant number of sectors. We also give a series of representative results for larger planets at greater distances, which strongly depend on the target magnitude and on the length and quality of the data. Conclusions. The TESS sample will provide the most important statistics for the global aim of measuring the planet occurrence rate around hot subdwarfs. The Kepler, K2, and CHEOPS data will allow us to search for planetary remnants, that is, very close and small (possibly disintegrating) objects.
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| 2. |
- Wikström, Victoria, et al.
(författare)
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Friction torque and slip of rollers in roller bearings under arctic conditions
- 1991
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Ingår i: Tezisy dokladov / Meždunarodnyj Sovetsko-Skandinavskij Seminar Mašiny, Materialy i Konstrukcii v Arktičeskich Uslovijach = Abstracts / International Soviet-Scandinavian Seminar Machines, Materials and Structures in Arctic Conditions.
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Konferensbidrag (refereegranskat)
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| 3. |
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| 4. |
- Östensen, J.O., et al.
(författare)
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Analysis of a grease-lubricated roller bearing under arctic conditions
- 1995
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Ingår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - 1350-6501 .- 2041-305X. ; 209:3, s. 213-220
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Tidskriftsartikel (refereegranskat)abstract
- This paper summarizes measurements of starting torque and motion of the rollers in a roller bearing during start-up at a temperature of -30 °C. The bearing was lubricated with three different greases and the tests were carried out after a running-in procedure at +20 °C. The results were compared with measurements obtained at +20 °C and with results from one base oil at +20 °C. A model for the roller motion was also built and simulations of the roller motion were compared with the measurements. Independent of temperature and lubricant the rollers rolled in the loaded zone and slipped, more or less, in the unloaded zone. The degree of sliding in the unloaded zone was found to be governed mainly by the local lubricant distribution and the position of the roller in the cage pocket. Some differences are also seen in the slide-roll ratio between the lubricants. A roller diameter difference of 1.3 μm gave a significant difference in roller motion, with the slightly thinner roller slides more in the unloaded zone of the bearing.
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| 5. |
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| 6. |
- Östensen, J. O.
(författare)
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Prediction of film thickness in an elastohydrodynamic point contact lubricated with a viscosity index improved base oil
- 1995
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Ingår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - 1350-6501 .- 2041-305X. ; 209:4, s. 235-242
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Tidskriftsartikel (refereegranskat)abstract
- A simple iterative method is used for the computation of the central film thickness in a fully flooded elastohydrodynamic (EHD) point contact lubricated with a polymeric viscosity index (V1)-improved base oil. The shear stress dependence of the Vl-improved base oil is included in the iterative method. Experimental data are presented on temporary viscosity loss and central film thickness at different temperatures from —8 to 40° C.A good approximation of the central film thickness in an EHD point contact lubricated with V1-improved oil is given by using an iterative method involving the temporary viscosity loss of the Vl-improved base oil. The central film thickness depends on the mean shear stress at the inlet of the contact, and this shear-thinning effect has been accounted for in the calculations.
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