Margrethe Wold

• Ho, Alex; Wold, Margrethe; Poursina, Mohammad & Conway, John Thomas (2023). The accuracy of mutual potential approximations in simulations of binary asteroids. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 671. doi: 10.1051/0004-6361/202245552. Vis sammendrag

  Context. Simulations of asteroid binaries commonly use mutual gravitational potentials approximated by series expansions, leading to truncation errors, and also preventing correct computations of force and torque for certain configurations where the bodies have overlapping bounding spheres, such as in the rotational fission model for creating asteroid binaries and pairs. Aims. We address errors encountered when potentials truncated at order two and four are used in simulations of binaries, as well as other errors related to configurations with overlapping bounding spheres where the series diverge. Methods. For this we utilized a recently developed method where the gravitational interaction between two triaxial ellipsoids can be calculated without approximations for any configuration. The method utilizes surface integration for both force and torque calculations, and it is exact for ellipsoidal shapes. We also computed approximate solutions using potentials truncated at second and fourth order, and we compare these with the solutions obtained with the surface integral method. The approximate solutions were generated with the “General Use Binary Asteroid Simulator” (GUBAS). Results. If the secondary is located with its centroid in the equatorial plane of the primary, the error in the force increases as the secondary is moved closer to the primary, but is still relatively small for both second and fourth order potentials. For torque calculations, the errors become more significant, especially if the other body is located close to one of the extended principal axes. On the axes themselves, the second order series approximation fails by 100%. For dynamical simulations of components separated a few primary radii apart, the fourth order approximation is significantly more accurate than the second order. Furthermore, because of larger errors in the torque calculations, the rotational motion is subject to greater inaccuracies than the translational motion. For configurations resembling contact binaries where the bounding spheres overlap, the errors in both force and torque in the initial stages of the simulation are considerable, regardless of the approximation order, because the series diverge. A comparison of the computational efficiency of the force and torque calculations shows that the surface integration method is approximately 82 times and four times slower than the second and fourth order potentials, respectively, but approximately 16 times faster than the order eight potential. Comparing the computation efficiency of full simulations, including the calculations of the equations of motion, shows that the surface integration scheme is comparable with GUBAS when an order four potential is used. Conclusions. The errors generated when mutual gravitational potentials are truncated at second or fourth order lead to larger errors in the rotational than in the translational motion. Using a mathematically exact method for computing forces and torques becomes important when the bodies are initially close and the bounding spheres overlap, in which case both the translational and rotational motion of the bodies have large errors associated with them. For simulations with two triaxial ellipsoids, the computational efficiency of the surface integral method is comparable to fourth order approximations with GUBAS, and superior to eight order or higher.

• Ho, Alex; Wold, Margrethe; Poursina, Mohammad & Conway, John Thomas (2022). Dynamics of asteroid systems post-rotational fission. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 665. doi: 10.1051/0004-6361/202243706. Fulltekst i vitenarkiv
• Ho, Alex; Wold, Margrethe; Conway, John Thomas & Poursina, Mohammad (2021). Extended two-body problem for rotating rigid bodies. Celestial mechanics & dynamical astronomy. ISSN 0923-2958. 133. doi: 10.1007/s10569-021-10034-8. Fulltekst i vitenarkiv Vis sammendrag

  A new technique that utilizes surface integrals to find the force, torque and potential energy between two non-spherical, rigid bodies is presented. The method is relatively fast, and allows us to solve the full rigid two-body problem for pairs of spheroids and ellipsoids with 12 degrees of freedom. We demonstrate the method with two dimensionless test scenarios, one where tumbling motion develops, and one where the motion of the bodies resemble spinning tops. We also test the method on the asteroid binary (66391) 1999 KW4, where both components are modelled either as spheroids or ellipsoids. The two different shape models have negligible effects on the eccentricity and semi-major axis, but have a larger impact on the angular velocity along the z-direction. In all cases, energy and total angular momentum is conserved, and the simulation accuracy is kept at the machine accuracy level.

• Wold, Margrethe & Conway, John Thomas (2021). The planar two-body problem for spheroids and disks. Celestial mechanics & dynamical astronomy. ISSN 0923-2958. 133. doi: 10.1007/s10569-021-10023-x. Fulltekst i vitenarkiv
• Wold, Margrethe (2018). Students' usage patterns of video recorded lectures in an undergraduate mathematics course . International Network for Didactic Research in University Mathematics : INDRUM. ISSN 2496-1027. s. 370–371.
• Gjesteland, Thomas; Vos, Pauline & Wold, Margrethe (2018). Mathematical modelling and activation – a study on a large class, a project-based task and students’ flow. International Network for Didactic Research in University Mathematics : INDRUM. ISSN 2496-1027. s. 175–184. Vis sammendrag

  We studied how engineering students in a large class (n=346) can be activated by a project-based task, in which they have to model mathematically the motion of an object. The students had to throw an object, use (1) their smart phones for filming, and (2) tracker software for capturing the motion. Through a poster, they had to report their video analysis. We framed activation through the concept of flow, which is a state of being fully absorbed by an activity. We administered a web-based questionnaire (response rate 69%). The results show that such a project-based task is feasible with >300 students and activated them: three out of five experienced flow. Also, we validated the theory that for experiencing flow, a task must be perceived as challenging and that one’s skills should match that challenge.

• Gjesteland, Thomas; Vos, Pauline & Wold, Margrethe (2017). Students experiencing flow in a Physics lab task using mobile phones and free software. I Tveiten, Oddgeir (Red.), Smart Universities: Education´s Digital Future. Logos Verlag Berlin. ISSN 978-3-8325-4595-6. s. 37–44.
• Hogner, Silje; Riera, Albert Burgas; Wold, Margrethe; Lifjeld, Jan Terje & Johnsen, Arild (2015). Intergeneric hybridization between Common Redstart Phoenicurus phoenicurus and Whinchat Saxicola rubetra revealed by molecular analyses. Journal of Ornithology. ISSN 2193-7192. 156, s. 829–836. doi: 10.1007/s10336-015-1165-x.
• Toft, Sune; Gallazzi, Anna; Zirm, Andrew; Wold, Margrethe; Zibetti, S. & Grillo, C. [Vis alle 7 forfattere av denne artikkelen] (2012). Deep absorption line studies of quiescent galaxies at z~2: The dynamical-mass-size-relation and first contraints on the fundamental plane. The Astrophysical Journal (ApJ). ISSN 0004-637X. 754. doi: 10.1088/0004-637X/754/1/3.
• Hiner, Kyle; Canalizo, Gabriela; Wold, Margrethe; Brotherton, Michael S. & Cales, Sabrina L. (2012). Black-hole-bulge relationship of post-starburst quasars at z~0.3. The Astrophysical Journal (ApJ). ISSN 0004-637X. 756. doi: 10.1088/0004-637X/756/2/162.
• Canalizo, Gabriela; Wold, Margrethe; Hiner, Kyle; Lacy, Mark & Aylor, Kevin (2012). Probing the M-sigma relation in the non-local universe using red qsos. The Astrophysical Journal (ApJ). ISSN 0004-637X. 760. doi: 10.1088/0004-637X/760/1/38.
• Wold, Margrethe; Brotherton, M. S. & Shang, Z. (2008). Quasar Optical Variability and Black Hole Mass. Revista mexicana de astronomía y astrofísica. ISSN 0185-1101. 32, s. 15–17.
• Canalizo, G.; Wold, Margrethe; Lazarova, M. & Lacy, Mark (2008). Quasar Black Hole Masses from Velocity Dispersions. AIP Conference Proceedings. ISSN 0094-243X. 1053, s. 63–66. doi: 10.1063/1.3009525. Vis sammendrag

  Much progress has been made in measuring black hole (BH) masses in (non-active) galactic nuclei using the tight correlation between stellar velocity dispersions σ in galaxies and the mass of their central BH. The use of this correlation in quasars, however, is hampered by the difficulty in measuring sigma in host galaxies that tend to be overpowered by their very bright nuclei. We discuss results from a project that focuses on z~0.3 quasars suffering from heavy extinction at shorter wavelengths. This makes it possible to obtain clean spectra of the hosts in the spectral regions of interest, while broad lines (like Hα) are still visible at longer wavelengths. We compare BH masses obtained from velocity dispersions to those obtained from the BLR and thus probe the evolution of this relation and BH growth with redshift and luminosity. Our preliminary results show an offset between the position of our objects and the local relation, in the sense that red quasars have, on average, lower velocity dispersions than local galaxies. We discuss possible biases and systematic errors that may affect our results.

• Wold, Margrethe; Brotherton, M. S. & Shang, Z. (2008). Black hole mass and variability in quasars. AIP Conference Proceedings. ISSN 0094-243X. 1053, s. 55–58. doi: 10.1063/1.3009523.
• Wold, Margrethe; Brotherton, M. S. & Shang, Z. (2008). Black hole mass and variability in quasars. I Chakrabarti, Sandip K. & Majumdar, Archan S. (Red.), Observational evidence for black holes in the universe. AIP Publishing (American Institute of Physics). ISSN 978-0-7354-0582-0. Vis sammendrag

  We report on a study that finds a positive correlation between black hole mass and variability amplitude in quasars. Roughly 100 quasars at z<0.75 were selected by matching objects from the QUEST1 Variability Survey with broad‐lined objects from the Sloan Digital Sky Survey. Black hole masses were estimated with the virial method using the broad Hβ line, and variability was characterized from the QUEST1 light curves. The correlation between black hole mass and variability amplitude is significant at the 99% level or better and does not appear to be caused by obvious selection effects inherent to flux‐limited samples. It is most evident for rest frame time lags of the order a few months up to the QUEST1 maximum temporal resolution of about 2 years. The correlation between black hole mass and variability amplitude means that the more massive black holes have larger percentage flux variations. Over 2–3 orders of magnitude in black hole mass, the amplitude increases by ∼0.2 mag. A likely explanation for the correlation is that the more massive black holes are starving and produce larger flux variations because they do not have a steady inflow of gaseous fuel. Assuming that the variability arises from changes in the accretion rate Li & Cao [8] show that flux variations similar to those observed are expected as a consequence of the more massive black holes having cooler accretion disks.

• Wold, Margrethe; Brotherton, M. S. & Shang, Z. (2007). The dependence of quasar variability on black hole mass. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 375, s. 989–999.
• de Diego, J.A.; Binette, L.; Ogle, P.; Anderson, A.C.; Haro-Corzo, S. & Wold, Margrethe (2007). Quasar 3C298: a test-case for meteoritic nanodiamond 3.5micron emission. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 467, s. L7–L10.
• Wold, Margrethe; Lacy, Mark & Armus, Lee (2007). The influence of AGN nuclear parameters on the FRI/FRII dichotomy. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 470, s. 531–538. doi: 10.1051/0004-6361:20065266.
• Sollerman, J.; Jaunsen, Andreas Ortmann; Fynbo, J.P.U.; Hjorth, J; Jakobsson, P. & Stritzinger, M. [Vis alle 26 forfattere av denne artikkelen] (2006). Supernova 2006aj and the associated X-Ray Flash 060218. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 454, s. 503–509. doi: 10.1051/0004-6361:20065226.
• Wold, Margrethe & Galliano, E. (2006). Nuclear embedded star clusters in NGC 7582. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 369.
• Müller, A. & Wold, Margrethe (2006). On the signatures of gravitational redshift: The onset of relativistic emission lines. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 457. doi: 10.1051/0004-6361:20065615.
• Wold, Margrethe; Lacy, Mark; Kaufl, H.U. & Siebenmorgen, R. (2006). The nuclear regions of NGC 7582 from [Ne II] spectroscopy at 12.8 μm - an estimate of the black hole mass. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 460(449). doi: 10.1051/0004-6361:20053385.
• McLure, R.; Lacy, Mark; Willott, C.J.; Jarvis, M.J.; Rawlings, S. & Hill, G. [Vis alle 9 forfattere av denne artikkelen] (2004). A sample of radio galaxies spanning three decades in radio luminosity - I. The host galaxy properties and black hole masses. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 351.
• Wold, Margrethe; Armus, L.; Neugebauer, G.; Jarrett, T.H. & Lehnert, M. (2003). Overdensities of extremely red objects in the fields of high-redshift QSOs. Astronomical Journal. ISSN 0004-6256. 126.
• Wold, Margrethe; Lacy, Mark; Dahle, H. & Lilje, Per Barth (2002). AGN-selected clusters as revealed by weak lensing. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 355.
• Wold, Margrethe; Lacy, Mark; Lilje, Per Barth & Serjeant, Stephen (2001). Radio-quiet quasar environments at 0.5 < z < 0.8. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 323.
• Wold, Margrethe; Lacy, Mark; Lilje, Per Barth & Serjeant, Stephen (2000). Clustering of galaxies around radio quasars at 0.5 < z < 0.8. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 316.
• Lacy, Mark; Ridgway, S.; Wold, Margrethe; Lilje, Per Barth & Rawlings, S. (1999). Radio-optical alignments in a low radio luminosity sample. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 307.
• Pedersen, H.; Jaunsen, A.O.; Grav, T.; Østensen, R.; Andersen, M.I. & Wold, Margrethe [Vis alle 27 forfattere av denne artikkelen] (1998). Evidence for diverse optical emission from gamma-ray burst sources. The Astrophysical Journal (ApJ). ISSN 0004-637X. 496. doi: 10.1086/305385.
• Castro-Tirado, A.J.; Gorosabel, J; Benitez, N.; Wolf, C.; Fockenbrock, R. & Martínez-González, E. [Vis alle 27 forfattere av denne artikkelen] (1998). Photometry and spectroscopy of the GRB 970508 optical counterpart. Science. ISSN 0036-8075. 279(1011). doi: 10.1126/science.279.5353.1011.

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• Wold, Margrethe; Ho, Alex; Poursina, Mohammad & Conway, John Thomas (2022). Two-body interactions with surface integrals.
• Ho, Alex; Wold, Margrethe; Conway, John Thomas & Poursina, Mohammad (2021). Dynamics of Asteroid Binary Systems through the Use of Surface Integrals.
• Wold, Margrethe (2020). NRK Sørlandet, intervju om vintersolverv og Saturn og Jupiters konjunksjon i desember 2020. [Radio]. NRK Sørlandet.
• Wold, Margrethe; Conway, John Thomas & Ho, Alex (2019). The planar rigid two-body problem.
• Wold, Margrethe (2019). On black holes.
• Wold, Margrethe (2019). Måneformørkelse 2019. [TV]. NRK radio og TV.
• Wold, Margrethe (2019). Astronomi.
• Wold, Margrethe (2018). Nobelprisen 2017 og oppdagelsen av gravitajonsbølger .
• Wold, Margrethe (2018). Stephen Hawking - hans utrolige liv og banebrytende forskning.
• Wold, Margrethe (2018). Student's usage patterns of video recorded lectures in an undergraduate mathematics course.
• Wold, Margrethe (2018). Om Nobelprisen i fysikk 2017. I Jahr, Ernst Håkon; Nossum, Rolf Tomas; Thygesen, Ragnar & Breen, Olav (Red.), Agder Vitenskapsakademi, Årbok 2017. Portal forlag. ISSN 978-82-02-59723-8. s. 224–227.
• Wold, Margrethe (2017). Om Nobelprisen i fysikk 2017.
• Wold, Margrethe (2017). Nobelprisen i fysikk 2016. I Jahr, Ernst Håkon; Håland Knutson, Inger Johanne; Nossum, Rolf Tomas & Breen, Olav (Red.), Agder Vitenskapsakademi - Årbok 2016 . Portal forlag. ISSN 978-82-8314-153-5. s. 242–246.
• Gjesteland, Thomas; Vos, Pauline & Wold, Margrethe (2017). Students experiencing flow in a Physics lab task using mobile phones and free software.
• Gjesteland, Thomas; Vos, Pauline & Wold, Margrethe (2016). Students Experiencing Flow in a Physic Laboratory Task using Mobile Phones and Free Software.
• Wold, Margrethe (2016). Nobelprisen i fysikk 2016, foredrag.
• Wold, Margrethe (2016). Moderne astronomi.
• Wold, Margrethe (2015). Nobelprisen i fysikk 2014: Blå lysdioder. I Jahr, Ernst Håkon; Nossum, Rolf Tomas; Storesletten, Leiv & Breen, Olav (Red.), Agder Vitenskapsakademi - Årbok 2014. Portal forlag. ISSN 978-82-8314-034-7. s. 199–202.
• Wold, Margrethe; Røer, J.; Gundersen, G. & Kristiansen, V. (2013). Trekkfuglovervåking ved Lista og Jomfruland fuglestasjoner. Vår Fuglefauna. ISSN 0332-5601.
• Hiner, Kyle; Canalizo, Gabriela; Wold, Margrethe & Brotherton, Michael S. (2012). Measuring the M-sigma relation with quasars from 0.2 < z < 1.
• Canalizo, Gabriela; Wold, Margrethe; Hiner, Kyle; Lazarova, M.; Lacy, Mark & Aylor, K. (2012). Probing black hole - host galaxy relations using dust reddened qsos.
• Hiner, Kyle; Canalizo, Gabriela; Wold, Margrethe; Lazarova, M. & Lacy, Mark (2010). Investigating the M-sigma relation of red qsos.
• Skedsmo, Guri Leyell; Jaunsen, Andreas Ortmann; Wold, Margrethe; Langangen, Øystein; Mysen, Eirik & Dahle, Håkon [Vis alle 8 forfattere av denne artikkelen] (2008). En uendelighet av gåter. [Avis]. Verdens Gang 7 – søndagsmagasin.
• Synnevåg, Anne & Wold, Margrethe (2008). Sorte hull og galaksedannelse. [Radio]. NRK Verdt å vite.
• Spilde, Ingrid & Wold, Margrethe (2008). Det sorte hullet kom først. [Internett]. forskning.no.
• Wold, Margrethe (2008). Variability of active galaxies.
• Wold, Margrethe (2008). Dust-obscured quasars as probes of galaxy evolution.
• Wold, Margrethe (2008). AGN as probes of galaxy evolution.
• Wold, Margrethe (2008). Luminous infrared galaxies in the mid-infrared.
• Wold, Margrethe (2008). Black hole mass and variability in quasars. Vis sammendrag

  We report on a study that finds a positive correlation between black hole mass and variability amplitude in quasars. Roughly 100 quasars at z<0.75 were selected by matching objects from the QUEST1 Variability Survey with broad-lined objects from the Sloan Digital Sky Survey. Black hole masses were estimated with the virial method using the broad Hβ line, and variability was characterized from the QUEST1 light curves. The correlation between black hole mass and variability amplitude is significant at the 99% level or better and does not appear to be caused by obvious selection effects inherent to flux-limited samples. It is most evident for rest frame time lags of the order a few months up to the QUEST1 maximum temporal resolution of about 2 years. The correlation between black hole mass and variability amplitude means that the more massive black holes have larger percentage flux variations. Over 2-3 orders of magnitude in black hole mass, the amplitude increases by ~0.2 mag. A likely explanation for the correlation is that the more massive black holes are starving and produce larger flux variations because they do not have a steady inflow of gaseous fuel. Assuming that the variability arises from changes in the accretion rate Li & Cao [8] show that flux variations similar to those observed are expected as a consequence of the more massive black holes having cooler accretion disks.

• Wold, Margrethe (2008). Quasar Black Hole Masses from Velocity Dispersions.
• Wold, Margrethe; Brotherton, M. S. & Shang, Z. (2008). Black hole mass and variability in quasars.
• Wold, Margrethe (2007). Quasar variability and black hole mass.
• Wold, Margrethe (2007). Active galaxies: supermassive black holes and variability.
• Wold, Margrethe (2007). QSO variability and black hole mass.
• Wold, Margrethe & Lemstad, F. (1998). Svarte legemer - stråling og temperatur. Astronomi. ISSN 0802-7587.
• Wold, Margrethe (1998). Snart kan Universets skjebne avsløres. Astronomi. ISSN 0802-7587.
• Ho, Alex; Wold, Margrethe; Poursina, Mohammad & Conway, John Thomas (2023). Modeling asteroid binary systems with the full two-body problem using surface integrals. Universitetet i Agder. ISSN 978-82-8427-149-1. Fulltekst i vitenarkiv Vis sammendrag

  An asteroid binary system, where two asteroids are in mutual orbit, is important to study as it can provide knowledge of the history of the asteroid population. The most important mechanism to form asteroid binaries in the near-Earth population, and for asteroids with diameters less than 10 km, is rotational fission. Rotational fission occurs when a rubble pile asteroid, which can be thought of as a collection of rocks held together by gravity, reaches a critical spin rate and the rubble pile starts to shed mass. Studying the dynamics of asteroid binaries allows one to better understand how they have evolved. However, due to their non-spherical shapes, one has to take into account both the translational and rotational motion of asteroids, which is known as the full two-body problem. The study of the full two-body problem is a challenge as the mutual gravitational potential between two non-spherical bodies cannot be expressed analytically. Previous studies have used approximations to model the mutual potential between two asteroids. However, these approximations often suffer from inaccuracies when the bodies are close to each other, and also from truncation errors. In this thesis, we make use of a new method to determine the mutual potential, between two asteroids, with the use of surface integrals. We apply this method to study the dynamics of the 1999 KW4 binary system, where both bodies are modeled as ellipsoids. With the use of an order nine Runge-Kutta method, the system energy and angular momentum are conserved to the 11th decimal digit. One of the advantages of the surface integration method is that the results are valid even if the bodies are close to each other. We make use of this advantage to study the dynamics of asteroid systems formed by rotational fission, as the two bodies are very close to each other in the initial formation stages. We consider ellipsoidal bodies for the simulations. Six models are considered, three where the secondary takes different densities and three where we change the shape of the secondary. The simulations show that more than 80\% of the simulations result in the two bodies colliding. The secondary is more likely to escape the gravitational pull of the primary, forming an asteroid pair, and experience secondary fission, if the secondary has a higher density than the primary, or has a more elongated shape. We also compare the rotation periods of the bodies from the simulations with the ones from observations of asteroid binaries and pairs. The rotation periods from the simulations match very well with the rotation periods of observed asteroid pairs. The surface integration scheme can yield exact values to the mutual gravitational potential between two ellipsoidal bodies. This method can therefore be used to determine the accuracy of methods that approximates the mutual potential between two ellipsoids. We compare the surface integration scheme with an approach that expands the mutual potential with the use of inertia integrals. The differences in the gravitational force and torque, between the two methods, are less than 1\% if the bodies are separated by $2-3$ times the radius of the primary. If the bodies are almost touching, however, the differences can exceed 100\% if the shape of the primary becomes elongated. The discrepancies in the torques are typically an order magnitude larger than the difference in the forces.

• Imenes, Anne Gerd; Wold, Margrethe & Hasla, Helene Arnesen (2018). Measurements and Analysis of Spectral Irradiance Distributions in Southern Norway. Universitetet i Agder.
• Wold, Margrethe; Heggøy, Oddvar; Røer, J.; Nordsteien, O.; Aarvak, T. & Øien, J. (2015). Bestandsovervåking ved Jomfruland og Lista fuglestasjoner i 2013. Norsk Ornitologisk Forening. ISSN 978‐82‐78-52124-3.
• Wold, Margrethe; Røer, J.; Kristiansen, V.; Nordsteien, O.; Øien, J. & Aarvak, T. (2014). Bestandsovervåking ved Jomfruland og Lista fuglestasjoner i 2012. Norsk Ornitologisk Forening. ISSN 978-82-78-52116-8.
• Wold, Margrethe; Røer, J.E. & Bunes, V. (2012). Utvalgte fuglearters bruk av Listastrendene. Rapport for Miljøvernavdelingen, Fylkemannen i Vest-Agder. Fylkesmannen i Vest-Agder, Miljøvernavdelingen. Vis sammendrag

  Rapporten viser hvordan vann-, sjø- og våtmarkstilknyttede fuglearter bruker Listastendene landskapsvernområde året rundt.

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