The 44Ti-powered spectrum of SN 1987A

SN 1987A provides a unique opportunity to study the evolution of a supernova from explosion into very late phases. Due to the rich chemical structure, the multitude of physical process 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 (~8 years) HST 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 which is found to reproduce most of the lines in the observed spectrum to 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 emergent 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 emergent spectrum. Using the best available estimates for the dust extinction, we determine the amount of 44Ti produced in the explosion to 1.5\pm0.5 * 10^-4 Msun.Comment: 23 pages, 9 figures. 44Ti mass updated from 1.4E-4 to 1.5E-4 Msu

Teacher roles during amusement park visits – insights from observations, interviews and questionnaires

Amusement parks offer rich possibilities for physics learning, through observations and experiments that illustrate important physical principles and often involve the whole body. Amusement parks are also among the most popular school excursions, but very often the learning possibilities are underused. In this work we have studied different teacher roles and discuss how universities, parks or event managers can encourage and support teachers and schools in their efforts to make amusement park visits true learning experiences for their students

Radioactivities and nucleosynthesis in SN 1987A

The nucleosynthesis and production of radioactive elements in SN 1987A are reviewed. Different methods for estimating the masses of 56Ni, 57Ni, and 44Ti are discussed, and we conclude that broad band photometry in combination with time-dependent models for the light curve gives the most reliable estimates.Comment: 8 pages, 4 figs. Proceedings of the workshop "Astronomy with Radioactivities III", special issue of the "New Astronomy Reviews

The late-time light curve of the Type Ia supernova 2000cx

We have conducted a systematic and comprehensive monitoring programme of the Type Ia supernova 2000cx at late phases using the VLT and HST. The VLT observations cover phases 360 to 480 days past maximum brightness and include photometry in the BVRIJH bands, together with a single epoch in each of U and Ks. While the optical bands decay by about 1.4 mag per 100 days, we find that the near-IR magnitudes stay virtually constant during the observed period. This means that the importance of the near-IR to the bolometric light curve increases with time. The finding is also in agreement with our detailed modeling of a Type Ia supernova in the nebular phase. In these models, the increased importance of the near-IR is a temperature effect. We note that this complicates late-time studies where often only the V band is well monitored. In particular, it is not correct to assume that any optical band follows the bolometric light curve at these phases, and any conclusions based on such assumptions, e.g., regarding positron-escape, must be regarded as premature. A very simple model where all positrons are trapped can reasonably well account for the observations. The nickel mass deduced from the positron tail of this light curve is lower than found from the peak brightness, providing an estimate of the fraction of late-time emission that is outside of the observed wavelength range. Our detailed models show the signature of an infrared catastrophe at these epochs, which is not supported by the observations.Comment: Accepted by A&A, bitmapped figure

Outreach initiatives operated by universities for increasing interest in science and technology

This is an Accepted Manuscript of an article published by Taylor & Francis in European Journal of Engineering Edutaion on 2016, available online: http://www.tandfonline.com/10.1080/03043797.2015.1121468Since 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.Gumaelius, L.; Almqvistb, M.; Arnadottir, A.; Axelsson, A.; Conejero, JA.; García Sabater, JP.; Klitgaard, L.... (2016). Outreach initiatives operated by universities for increasing interest in science and technology. European Journal of Engineering Education. 41(6):589-622. https://doi.org/10.1080/03043797.2015.1121468S58962241

Catching Element Formation In The Act

Gamma-ray astronomy explores the most energetic photons in nature to address some of the most pressing puzzles in contemporary astrophysics. It encompasses a wide range of objects and phenomena: stars, supernovae, novae, neutron stars, stellar-mass black holes, nucleosynthesis, the interstellar medium, cosmic rays and relativistic-particle acceleration, and the evolution of galaxies. MeV gamma-rays provide a unique probe of nuclear processes in astronomy, directly measuring radioactive decay, nuclear de-excitation, and positron annihilation. The substantial information carried by gamma-ray photons allows us to see deeper into these objects, the bulk of the power is often emitted at gamma-ray energies, and radioactivity provides a natural physical clock that adds unique information. New science will be driven by time-domain population studies at gamma-ray energies. This science is enabled by next-generation gamma-ray instruments with one to two orders of magnitude better sensitivity, larger sky coverage, and faster cadence than all previous gamma-ray instruments. This transformative capability permits: (a) the accurate identification of the gamma-ray emitting objects and correlations with observations taken at other wavelengths and with other messengers; (b) construction of new gamma-ray maps of the Milky Way and other nearby galaxies where extended regions are distinguished from point sources; and (c) considerable serendipitous science of scarce events -- nearby neutron star mergers, for example. Advances in technology push the performance of new gamma-ray instruments to address a wide set of astrophysical questions.Comment: 14 pages including 3 figure

Late Spectral Evolution of SN 1987A: I. Temperature and Ionization

The temperature and ionization of SN 1987A is modeled between 200 and 2000 days in its nebular phase, using a time-dependent model. We include all important elements, as well as the primary composition zones in the supernova. The energy input is provided by radioactive decay of Co-56, Co-57, and Ti-44. The thermalization of the resulting gamma-rays and positrons is calculated by solving the Spencer-Fano equation. Both the ionization and the individual level populations are calculated time-dependently. Adiabatic cooling is included in the energy equation. Charge transfer is important for determining the ionization and is included with available and estimated rates. Full, multilevel atoms are used for the observationally important ions. As input models to the calculations we use explosion models for SN 1987A calculated by Woosley et al and Nomoto et al. The most important result in this paper refers to the evolution of the temperature and ionization of the various abundance zones. The metal-rich core undergoes a thermal instability, often referred to as the IR-catastrophe, at 600 - 1000 days. The hydrogen-rich zones evolve adiabatically after 500 - 800 days, while in the helium region both adiabatic cooling and line cooling are of equal importance after ~1000 days. Freeze-out of the recombination is important in the hydrogen and helium zones. Concomitant with the IR-catastrophe, the bulk of the emission shifts from optical and near-IR lines to the mid- and far-IR. After the IR-catastrophe, the cooling is mainly due to far-IR lines and adiabatic expansion. Dust cooling is likely to be important in the zones where dust forms. We find that the dust condensation temperatures occur later than ~500 days in the oxygen-rich zones, and the most favorable zone for dust condensation is the iron core.Comment: 53 pages, including 10 figures; ApJ (Main Journal); scheduled for April 1, 1998, Vol. 49