| 1. |
- Ergon, Mattias, et al.
(författare)
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Monte-Carlo methods for NLTE spectral synthesis of supernovae
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 620
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Tidskriftsartikel (refereegranskat)abstract
- We present JEKYLL, a new code for modelling of supernova (SN) spectra and lightcurves based on Monte-Carlo (MC) techniques for the radiative transfer. The code assumes spherical symmetry, homologous expansion and steady state for the matter, but is otherwise capable of solving the time-dependent radiative transfer problem in non-local-thermodynamic-equilibrium (NLTE). The method used was introduced in a series of papers by Lucy, but the full time-dependent NLTE capabilities of it have never been tested. Here, we have extended the method to include non-thermal excitation and ionization as well as charge-transfer and two-photon processes. Based on earlier work, the non-thermal rates are calculated by solving the Spencer-Fano equation. Using a method previously developed for the SUMO code, macroscopic mixing of the material is taken into account in a statistical sense. To save computational power a diffusion solver is used in the inner region, where the radiation field may be assumed to be thermalized. In addition, a statistical Markov-chain model is used to sample the emission frequency more efficiently, and we introduce a method to control the sampling of the radiation field, which is used to reduce the noise in the radiation field estimators. Except for a description of JEKYLL, we provide comparisons with the ARTIS, SUMO and CMFGEN codes, which show good agreement in the calculated spectra as well as the state of the gas. In particular, the comparison with CMFGEN, which is similar in terms of physics but uses a different technique, shows that the Lucy method does indeed converge in the time-dependent NLTE case. Finally, as an example of the time-dependent NLTE capabilities of JEKYLL, we present a model of a Type IIb SN, taken from a set of models presented and discussed in detail in an accompanying paper. Based on this model we investigate the effects of NLTE, in particular those arising from non-thermal excitation and ionization, and find strong effects even on the bolometric lightcurve. This highlights the need for full NLTE calculations when simulating the spectra and lightcurves of SNe.
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| 2. |
- Fransson, Claes, et al.
(författare)
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Hubble Space Telescope and Ground-based Observations of SN 1993J and SN 1998S : CNO Processing in the Progenitors
- 2005
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 622, s. 991-1007
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Tidskriftsartikel (refereegranskat)abstract
- Ground-based and Hubble Space Telescope observations are presented for SN 1993J and SN 1998S. SN 1998S shows strong, relatively narrow circumstellar emission lines of N III-V and C III-IV, as well as broad lines from the ejecta. Both the broad ultraviolet and optical lines in SN 1998S indicate an expansion velocity of ~7000 km s-1. The broad emission components of Lyα and Mg II are strongly asymmetrical after day 72 past the explosion and differ in shape from Hα. Different models based on dust extinction from dust in the ejecta or shock region, in combination with Hα from a circumstellar torus, are discussed. It is concluded, however, that the double-peaked line profiles are more likely to arise as a result of optical depth effects in the narrow, cool, dense shell behind the reverse shock than in a torus-like region. The ultraviolet lines of SN 1993J are broad, with a boxlike shape, coming from the ejecta and a cool, dense shell. The shapes of the lines are well fitted by a shell with inner velocity ~7000 km s-1 and outer velocity ~10,000 km s-1. For both SN 1993J and SN 1998S a strong nitrogen enrichment is found, with N/C~12.4 in SN 1993J and N/C~6.0 in SN 1998S. From a compilation of all supernovae with determined CNO ratios, we discuss the implications of these observations for the structure of the progenitors of Type II supernovae. Based in part on observations obtained with the Hubble Space Telescope, which is operated by AURA, Inc., under NASA contract NAS 5-26555.
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| 3. |
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| 4. |
- Gumaelius, Lena, et al.
(författare)
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Outreach initiatives operated by universities for increasing interest in science and technology
- 2016
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Ingår i: European Journal of Engineering Education. - : Taylor & Francis Group. - 0304-3797 .- 1469-5898. ; , s. 1-34
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Tidskriftsartikel (refereegranskat)abstract
- Since the 1990s, the low number of students choosing to study science and technology in higher education has been on the societal agenda and many initiatives have been launched to promote awareness regarding career options. The initiatives particularly focus on increasing enrolment in the engineering programmes. This article describes and compares eight European initiatives that have been established and operated by universities (and in some cases through collaboration with other actors in society). Each initiative is summarised in a short essay that discusses motivation, organisation, pedagogical approach, and activities. The initiatives are characterised by comparing the driving forces behind their creation, how the initiative activities relate to the activities at the university, size based on the number of participants and cost per participant and pedagogical framework. There seem to be two main tracks for building outreach activities, one where outreach activities are based on the university's normal activities, and one where outreach activities are designed specifically for the visiting students.
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| 5. |
- Hartell, Eva, 1973-, et al.
(författare)
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K-ULF : Creating Research Synergy in the Interface Between School and the Academy
- 2021
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Ingår i: PATT38 Book of Abstracts.. - Turku, Finland : PATT Organizing Committee. ; , s. 27-28
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Konferensbidrag (refereegranskat)abstract
- The K-ULF project is part of a Swedish government initiative, to develop and evaluate sustainable collaboration models for empirical participatory research. The primary aim is to strengthen the research base for educational practice in schools through integrating the teaching profession and its development with university research and teacher education. Participatory research and co-design of teaching and learning studies is seen as a way to achieve the aim of strengthening the scientific ground and proven experience in education on a national level. Within the context of this initiative K-ULF places particular emphasis on egalitarianism in the context of schools and education. The project explores the role of practical work (laboratories and experimental curricula) on digital competencies and language development in STEM education. Studies conducted following the K-ULF model are a collaborative venture gathering teachers, teacher students, teacher educators and educational researchers at KTH Royal Institute of Technology and three municipalities Haninge, Lidingö and Stockholm, in Sweden. The K-ULF project is tightly integrated with KTH’s teacher education programs, involving students in their teaching rounds and their master thesis work. During the school visits they collect observational data documenting classroom practice and student learning behaviors. Master degree students thesis work is conducted in collaboration with mentors at schools in the end of the degree. K-ULF integrates classroom-based research and innovation with teaching degrees using a participatory Scholarship of Teaching and Learning model. This provides schools with direct participation in research closely connected to educational practices, helping to build a culture of research driven change in school teaching as well as driving research relevant to teachers in a mutual exchange between academia and school. This need of participatory research has recently been emphasized in two large scale Swedish Government reports. This presentation provides an overview of K-ULF as well as an illustrative example from one of the K-ULF pilot schools, Fredrika Bremergymnasiet in Haninge. The context for the study is the technology program, a prerequisite upper secondary school program preparing pupils to study engineering at university. The result from the case study is a new course design in which a teacher student specialized in programming and an experienced teacher collaboratively developed a curriculum module for product development. The new approach combines class content by embedding programming into a pre-existing curriculum module of mechanical and hardware. The illustrative example above is one of several cases in which the K-ULF model contributes to strengthening the interface between school and academy.
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| 6. |
- Hartell, Eva, 1973-, et al.
(författare)
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K-ULF : an agile model for participatory practitioner-based research in STEM education
- 2022
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Ingår i: <em>11<sup>th</sup> Biennial International Design and Technology Teacher’s Association Research Conference (DATTArc). 7-10 Dec.2022. In collaboration with the International Conference on Technology Education (ICTE) – Asia Pacific, Technology Education New Zealand (TENZ), International Technology Engineering Education Association (ITEEA), and 2022 Venue Host, Southern Cross University, Gold Coast Campus, QLD. </em><em>Editors: Adj. Prof. Kurt Seemann and Prof. P John Williams.</em>. ; , s. 1-3
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Konferensbidrag (refereegranskat)abstract
- This extended abstract describes a project which develops STEM education, and a social justice and equal opportunity agenda, in which the school's egalitarianmission is seen as an imperative to support every child regardless of background. The K-ULF project (compensatory teaching and learning through practice-lead research[1]) takes an exploratory approach in developing and evaluating models for participatory practice-lead research. The initiative is a joint venture between academia and the Swedish school system. Traditionally teachers have seen more as the objects of study, rather than active agents in the creation of research questions, design or even results. The growing interest in evidence informed practice is gaining ground internationally, however the results of earlier studies may not always be relevant or when relevant not embedded in the learning and school culture in which they are used. The need for arenas where academia and practice collaborate, co-create, and learn from each other is desperately needed. Our aim is to develop models for participatory collaborative research where both researchers and teachers contribute, share, and create knowledge together. This approach has huge potential in terms of strengthening the research base for educational practices in schools and integrating the teaching profession and its development through collaboration with research and teacher education. K-ULF contributes to making research more relevant for educational practice in STEM education. The conference presentation presents the K-ULF model and its agile structure, inviting the audience torecontextualise our research into their own setting. [1] This is a loose translation from the Swedish name of the project.
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| 7. |
- Hartell, Eva, 1973-, et al.
(författare)
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K-ULF A Collaborative, Practitioner Research Model between School and Academia : Lessons learned
- 2022
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Ingår i: <em>Designing a better world through technological literacy for all. </em>. - St. John's, Newfoundland & Labrador, Canada : Faculty of Education, Memorial University, Canada. ; , s. 122-133
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Konferensbidrag (refereegranskat)abstract
- The K-ULF (Compensatory teaching for learning and research) project is part of a Swedishgovernment initiative, to develop and evaluate sustainable collaboration models for empiricalparticipatory research. Aiming to strengthen the research base for educational practice in schoolsthrough integrating the teaching profession and its development in collaboration with research andteacher education on a national level. Participatory research within K-ULF focuses on scholarshipof teaching and learning to strengthen the scientific foundation and professional experience basisfor Technology in K–12 STEM education. K-ULF contributes to increased knowledge and insightregarding how to design a model that supports the school’s compensatory mission in a strategic co-designed action research framework. This paper provides an overview of the collaborative researchmodels developed in this initial phase as well as a summary and analysis of the outcomes of theparticipatory research within the partnership between KTH’s teacher education and STEM teachersin five partner education providers.
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| 8. |
- Jerkstrand, Anders, 1978-, et al.
(författare)
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The 44Ti-powered spectrum of SN 1987A
- 2011
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 530, s. A45-
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Tidskriftsartikel (refereegranskat)abstract
- SN 1987A provides a unique opportunity to study the evolution of a supernova from explosion into very late phases. Owing to the rich chemical structure, the multitude of physical processes involved and extensive radiative transfer effects, detailed modeling is needed to interpret the emission from this and other supernovae. In this paper, we analyze the late-time (about eight years) Hubble Space Telescope spectrum of the SN 1987A ejecta, where 44Ti is the dominant power source. Based on an explosion model for a 19 Msun progenitor, we compute a model spectrum by calculating the degradation of positrons and gamma-rays from the radioactive decays, solving the equations governing temperature, ionization balance and NLTE level populations, and treating the radiative transfer with a Monte Carlo technique. We obtain a UV/optical/NIR model spectrum that reproduces most of the lines in the observed spectrum with good accuracy. We find non-local radiative transfer in atomic lines to be an important process also at this late stage of the supernova, with 30% of the emerging flux in the optical and NIR coming from scattering/fluorescence. We investigate the question of where the positrons deposit their energy, and favor the scenario where they are locally trapped in the Fe/He clumps by a magnetic field. Energy deposition into these largely neutral Fe/He clumps makes Fe I lines prominent in the emerging spectrum. With the best available estimates for the dust extinction, we determine the amount of 44Ti produced in the explosion to be 1.5+-0.5 Msun.
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| 9. |
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| 10. |
- Larsson, Josefin, et al.
(författare)
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X-ray illumination of the ejecta of supernova 1987A
- 2011
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 474:7352, s. 484-486
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Tidskriftsartikel (refereegranskat)abstract
- When a massive star explodes as a supernova, substantial amounts of radioactive elements-primarily (56)Ni, (57)Ni and (44)Ti-are produced(1). After the initial flash of light from shock heating, the fading light emitted by the supernova is due to the decay of these elements(2). However, after decades, the energy powering a supernova remnant comes from the shock interaction between the ejecta and the surrounding medium(3). The transition to this phase has hitherto not been observed: supernovae occur too infrequently in the Milky Way to provide a young example, and extragalactic supernovae are generally too faint and too small. Here we report observations that show this transition in the supernova SN 1987A in the Large Magellanic Cloud. From 1994 to 2001, the ejecta faded owing to radioactive decay of (44)Ti as predicted. Then the flux started to increase, more than doubling by the end of 2009. We show that this increase is the result of heat deposited by X-rays produced as the ejecta interacts with the surrounding material. In time, the X-rays will penetrate farther into the ejecta, enabling us to analyse the structure and chemistry of the vanished star.
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