47 research outputs found
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