596 research outputs found
Monte-Carlo methods for NLTE spectral synthesis of supernovae
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. In addition, a statistical Markov-chain model
is used to sample the emission frequency, and we introduce a method to control
the sampling of the radiation field. 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.Comment: Accepted for publication by Astronomy & Astrophysic
Breeding for intercropping: the case of red clover persistence in grasslands
Legumes are important in sustainable agriculture and particularly so when they are intercropped with other species. In breeding programs, little attention is paid to their agronomic performance in species mixtures. In red clover, improved persistence is an important breeding goal. We identified traits associated with survival of red clover cultivated in pure stands (PS 3) or in mixtures with grasses (MS 3) and managed under a 3-cut system (two locations), as well as in pure stands in a 5-cut system (PS 5, one location). Survivors from replicate plots were collected and a new generation made from each plot. The new generations were characterized in a growth experiment with light or simulated shade, and in a freezing experiment. We show that the traits related to red clover persistence depend on both plant community composition and cutting frequency. MS 3 had more leaves with larger leaf blades and longer petioles during the vegetative stage, followed by earlier stem elongation, higher number of elongating stems, higher biomass (also when accounting for earlier stem elongation) and more leaves in the regrowth after cutting than PS 3. MS 3 also had better freezing tolerance. PS 5 was similar to MS 3 and different from PS 3 in the number of leaves, leaf blade size, petiole length and number of elongating stems. These results show that breeding and cultivar evaluation, which is currently almost exclusively considering performance in pure stands, may miss some variation which provides persistence of red clover in mixtures with grasses.Breeding for intercropping: the case of red clover persistence in grasslandspublishedVersio
Late-time spectral line formation in Type IIb supernovae, with application to SN 1993J, SN 2008ax, and SN 2011dh
We investigate line formation processes in Type IIb supernovae (SNe) from 100
to 500 days post-explosion using spectral synthesis calculations. The modeling
identifies the nuclear burning layers and physical mechanisms that produce the
major emission lines, and the diagnostic potential of these. We compare the
model calculations with data on the three best observed Type IIb SNe to-date -
SN 1993J, SN 2008ax, and SN 2011dh. Oxygen nucleosynthesis depends sensitively
on the main-sequence mass of the star and modeling of the [O I] 6300, 6364
lines constrains the progenitors of these three SNe to the M_ZAMS=12-16 M_sun
range (ejected oxygen masses 0.3-0.9 M_sun), with SN 2011dh towards the lower
end and SN 1993J towards the upper end of the range. The high ejecta masses
from M_ZAMS >= 17 M_sun progenitors give rise to brighter nebular phase
emission lines than observed. Nucleosynthesis analysis thus supports a scenario
of low/moderate mass progenitors for Type IIb SNe, and by implication an origin
in binary systems. We demonstrate how oxygen and magnesium recombination lines
may be combined to diagnose the magnesium mass in the SN ejecta. For SN 2011dh,
a magnesium mass of of 0.02-0.14 M_sun is derived, which gives a Mg/O
production ratio consistent with the solar value. Nitrogen left in the He
envelope from CNO-burning gives strong [N II] 6548, 6583 emission lines that
dominate over H-alpha emission in our models. The hydrogen envelopes of Type
IIb SNe are too small and dilute to produce any noticeable H-alpha emission or
absorption after ~150 days, and nebular phase emission seen around 6550 A is in
many cases likely caused by [N II] 6548, 6583. Finally, the influence of
radiative transport on the emergent line profiles is investigated...(abridged)Comment: Published versio
A metallicity study of 1987A-like supernova host galaxies
The origin of the blue supergiant (BSG) progenitor of Supernova (SN) 1987A
has long been debated, along with the role that its sub-solar metallicity
played. We now have a sample of 1987A-like SNe that arise from the core
collapse (CC) of BSGs. The metallicity of the explosion sites of the known BSG
SNe is investigated, as well as their association to star-forming regions. Both
indirect and direct metallicity measurements of 13 BSG SN host galaxies are
presented, and compared to those of other CC SN types. Indirect measurements
are based on the known luminosity-metallicity relation and on published
metallicity gradients of spiral galaxies. To provide direct estimates based on
strong line diagnostics, we obtained spectra of each BSG SN host both at the SN
explosion site and at the positions of other HII regions. Continuum-subtracted
Ha images allowed us to quantify the association between BSG SNe and
star-forming regions. BSG SNe explode either in low-luminosity galaxies or at
large distances from the nuclei of luminous hosts. Therefore, their indirectly
measured metallicities are typically lower than those of SNe IIP and Ibc. This
is confirmed by the direct estimates, which show slightly sub-solar values
(12+log(O/H)=8.3-8.4 dex), similar to that of the Large Magellanic Cloud (LMC),
where SN 1987A exploded. However, two SNe (1998A and 2004em) were found at near
solar metallicity. SNe IIb have a metallicity distribution similar to that of
BSG SNe. Finally, the association to star-forming regions is similar among BSG
SNe, SNe IIP and IIn. Our results suggest that LMC metal abundances play a role
in the formation of some 1987A-like SNe. This would naturally fit in a single
star scenario for the progenitors. However, the existence of two events at
nearly solar metallicity suggests that also other channels, e.g. binarity,
contribute to produce BSG SNe.Comment: 28 pages, 17 figures; accepted for publication (Astronomy and
Astrophysics); abstract abridged for arXiv submissio
Cultivar development of kelps for commercial cultivation - Past lessons and future prospects
Cultivated kelps and other macroalgae have great potential in future provision of food, feed, bioenergy, fertilizer, and raw material for a range of chemical products including pharmaceuticals, food and feed additives, and cosmetics. Only a few species are currently cultivated, almost exclusively in Asia. There is a range of species that could be utilized in different parts of the world, providing that protocols for reproduction, propagation, and cultivation are developed. Domestication of species involves selection of traits that are desirable in cultivation and in the utilization of the harvested biomass. Genetic improvement of cultivated species through recombination of alleles and selection (breeding) has ensured high productivity and product quality in both agri- and aquaculture and will likely do so for macroalgae cultivation and use as well. According to the published literature, genetic improvement of kelps in Asia has so far largely relied on utilization of heterosis expressed in certain combinations of parental material, sometimes species hybrids. Here, we explore and evaluate the various methods that could be used in kelp breeding and propose an initial simple and low-cost breeding strategy based on recurrent mixed hybridization and phenotypic selection within local populations. We also discuss the genetic diversity in wild populations, and how this diversity can be protected against genetic pollution, either by breeding and cultivating local populations, or by developing cultivars that are not able to establish in, or hybridize with, wild populations.publishedVersio
Quantitative genetics state-space modeling of phenotypic plasticity and evolution
Living organisms adapt to changes in environment by phenotypic plasticity and evolution by natural selection (or they migrate). At detailed genetic levels these phenomena are complicated, and quantitative genetics attempts to capture essential processes at a higher abstraction level. Phenotypic plasticity is then commonly modeled by reaction norms, which describe how individual traits in a population are expressed in response to changes in environmental variables. The mean reaction norms are evolvable, and here I present a general quantitative genetics state-space model for evolutionary reaction norm dynamics. Reaction norms make use of a reference environment, which is traditionally set to zero. This is problematic when the reference environment is the environment a population is adapted to, for the reason that this environment is a population property, which in itself may be evolvable. With reference to Ergon (2018), I describe models that take such evolvability into account. The resulting models are fundamentally different from most engineering system models, where given reference values are constant, and therefore without consequences can be set to zero. For simplicity I assume only temporal variations in environment, although there obviously are a lot of spatial variations in nature, and I assume that no mutations are involved. Fundamentals from quantitative evolutionary theory are given in appendices
Evolution of the progenitors of SNe 1993J and 2011dh revealed through late time radio and X-ray studies
We perform hydrodynamical simulations of the interaction between supernova
(SN) ejecta and circumstellar medium (CSM) for SN 1993J and SN 2011dh, and
calculate the radio and X-ray emissions expected from the shocked gas at late
epochs (). Considering the ejecta structure from multi-group radiation
hydrodynamics simulation, we find that the observed rapid drop in radio and
X-ray light curves of SN 1993J at 3000 days can be due to a change in the
mass-loss rate () around 6500 years prior to the explosion of the
SN. The exact epoch scales inversely with the assumed wind velocity of . The progenitor of this SN very likely belonged to a binary
system, where, during its evolution, the primary had transferred material to
the secondary. It is argued in the paper that the change in can happen
because of a change in the mass accretion efficiency () of the companion
star. It is possible that before years
prior to the explosion, was high, thus the CSM was tenuous, which causes
the late time downturn in fluxes. In the case of SN 2011dh, the late time
evolution is found to be consistent with a wind medium with . It is difficult from
our analysis to predict whether the progenitor of this SN had a binary
companion, however, if future observations show similar decrease in radio and
X-ray fluxes, then that would give strong support to a scenario where both SNe
had undergone similar kind of binary evolution before explosion.Comment: 13 pages, 10 figures; Accepted for publication in Ap
Metallicity at the explosion sites of interacting transients
Context. Some circumstellar-interacting (CSI) supernovae (SNe) are produced
by the explosions of massive stars that have lost mass shortly before the SN
explosion. There is evidence that the precursors of some SNe IIn were luminous
blue variable (LBV) stars. For a small number of CSI SNe, outbursts have been
observed before the SN explosion. Eruptive events of massive stars are named as
SN impostors (SN IMs) and whether they herald a forthcoming SN or not is still
unclear. The large variety of observational properties of CSI SNe suggests the
existence of other progenitors, such as red supergiant (RSG) stars with
superwinds. Furthermore, the role of metallicity in the mass loss of CSI SN
progenitors is still largely unexplored. Aims. Our goal is to gain insight on
the nature of the progenitor stars of CSI SNe by studying their environments,
in particular the metallicity at their locations. Methods. We obtain
metallicity measurements at the location of 60 transients (including SNe IIn,
SNe Ibn, and SN IMs), via emission-line diagnostic on optical spectra obtained
at the Nordic Optical Telescope and through public archives. Metallicity values
from the literature complement our sample. We compare the metallicity
distributions among the different CSI SN subtypes and to those of other
core-collapse SN types. We also search for possible correlations between
metallicity and CSI SN observational properties. Results. We find that SN IMs
tend to occur in environments with lower metallicity than those of SNe IIn.
Among SNe IIn, SN IIn-L(1998S-like) SNe show higher metallicities, similar to
those of SNe IIL/P, whereas long-lasting SNe IIn (1988Z-like) show lower
metallicities, similar to those of SN IMs. The metallicity distribution of SNe
IIn can be reproduced by combining the metallicity distributions of SN IMs
(that may be produced by major outbursts of massive stars like LBVs) and SNe
IIP (produced by RSGs). The same applies to the distributions of the Normalized
Cumulative Rank (NCR) values, which quantifies the SN association to H II
regions. For SNe IIn, we find larger mass-loss rates and higher CSM velocities
at higher metallicities. The luminosity increment in the optical bands during
SN IM outbursts tend to be larger at higher metallicity, whereas the SN IM
quiescent optical luminosities tend to be lower. Conclusions. The difference in
metallicity between SNe IIn and SN IMs suggests that LBVs are only one of the
progenitor channels for SNe IIn, with 1988Z-like and 1998S-like SNe possibly
arising from LBVs and RSGs, respectively. Finally, even though linedriven winds
likely do not primarily drive the late mass-loss of CSI SN progenitors,
metallicity has some impact on the observational properties of these
transients. Key words. supernovae: general - stars: evolution - galaxies:
abundancesComment: Submitted to Astronomy and Astrophysics on 28/02/2015; submitted to
arXiv after the 1st referee repor
- …