85 research outputs found
Comprehensive Observations of the Bright and Energetic Type Iax SN 2012Z: Interpretation as a Chandrasekhar Mass White Dwarf Explosion
We present UV through NIR broad-band photometry, and optical and NIR
spectroscopy of Type Iax supernova 2012Z. The data set consists of both early
and late-time observations, including the first late phase NIR spectrum
obtained for a spectroscopically classified SN Iax. Simple model calculations
of its bolometric light curve suggest SN 2012Z produced ~0.3 M_sun of (56)Ni,
ejected about a Chandrasekhar mass of material, and had an explosion energy of
~10^51 erg, making it one of the brightest and most energetic SN Iax yet
observed. The late phase NIR spectrum of SN 2012Z is found to broadly resemble
similar epoch spectra of normal SNe Ia; however, like other SNe Iax,
corresponding visual-wavelength spectra differ substantially compared to all
supernova types. Constraints from the distribution of IMEs, e.g. silicon and
magnesium, indicate that the outer ejecta did not experience significant mixing
during or after burning, and the late phase NIR line profiles suggests most of
the (56)Ni is produced during high density burning. The various observational
properties of SN 2012Z are found to be consistent with the theoretical
expectations of a Chandrasekhar mass white dwarf progenitor that experiences a
pulsational delayed detonation, which produced several tenths of a solar mass
of (56)Ni during the deflagration burning phase and little (or no) (56)Ni
during the detonation phase. Within this scenario only a moderate amount of
Rayleigh-Taylor mixing occurs both during the deflagration and fallback phase
of the pulsation, and the layered structure of the IMEs is a product of the
subsequent denotation phase. The fact that the SNe Iax population does not
follow a tight brightness-decline relation similar to SNe Ia can then be
understood in the framework of variable amounts of mixing during pulsational
rebound and variable amounts of (56)Ni production during the early subsonic
phase of expansion.Comment: Submitted to A&A, manuscript includes response to referee's comments.
39 pages, including 16 figures, 9 table
Extensive HST Ultraviolet Spectra and Multi-wavelength Observations of SN 2014J in M82 Indicate Reddening and Circumstellar Scattering by Typical Dust
SN 2014J in M82 is the closest detected Type Ia supernova (SN Ia) in at least
28 years and perhaps in 410 years. Despite its small distance of 3.3 Mpc, SN
2014J is surprisingly faint, peaking at V = 10.6 mag, and assuming a typical SN
Ia luminosity, we infer an observed visual extinction of A_V = 2.0 +/- 0.1 mag.
But this picture, with R_V = 1.6 +/- 0.2, is too simple to account for all
observations. We combine 10 epochs (spanning a month) of HST/STIS ultraviolet
through near-infrared spectroscopy with HST/WFC3, KAIT, and FanCam photometry
from the optical to the infrared and 9 epochs of high-resolution TRES
spectroscopy to investigate the sources of extinction and reddening for SN
2014J. We argue that the wide range of observed properties for SN 2014J is
caused by a combination of dust reddening, likely originating in the
interstellar medium of M82, and scattering off circumstellar material. For this
model, roughly half of the extinction is caused by reddening from typical dust
(E(B-V ) = 0.45 mag and R_V = 2.6) and roughly half by scattering off LMC-like
dust in the circumstellar environment of SN 2014J.Comment: 17 pages (excluding references and tables), 15 figures, accepted to
MNRAS. A high-resolution HST image of SN 2014J in M82 is available upon
reques
News discourse and readers’ comments: expanding the range of citizenship positions?
First Published May 15, 2017.Little attention has been paid to the relation between citizens’ representation in news media and citizen participation in readers’ comments, and to the roles both discourses may play in fostering public engagement in official consultation processes. This article offers a discursive analysis of these questions by focusing on how commenters, through their uses of language in connection with news texts, address the political ordering of news discourse and their positioning therein. Using Critical Discourse Analysis and other interaction-oriented forms of discourse analysis, we examine, first, the topics and the framing of voices in news coverage and, second, the interactional order, stance markers and style features of readers’ comments. Based on data regarding a policy plan on hydroelectric power in Portugal that was submitted to public consultation, we show that citizen positionings emerging from the interaction between news texts and comments change the balance of power within the discussion, but their participatory potential is restrained by traditional citizenship regimes.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was developed for the project COMPOLIS: 'Communication and Political Engagement with Environmental Issues' and supported by the Fundacao para a Ciencia e a Tecnologia (Portugal) [grant number EXPL/IVC-COM/1717/2012] through national funds (PIDDAC) and co-funded by the European Fund of Regional Development (FEDER) through COMPETE - Operational Program Competitive Factors (POFC).info:eu-repo/semantics/publishedVersio
Strong Ultraviolet Pulse From a Newborn Type Ia Supernova
Type Ia supernovae are destructive explosions of carbon oxygen white dwarfs.
Although they are used empirically to measure cosmological distances, the
nature of their progenitors remains mysterious, One of the leading progenitor
models, called the single degenerate channel, hypothesizes that a white dwarf
accretes matter from a companion star and the resulting increase in its central
pressure and temperature ignites thermonuclear explosion. Here we report
observations of strong but declining ultraviolet emission from a Type Ia
supernova within four days of its explosion. This emission is consistent with
theoretical expectations of collision between material ejected by the supernova
and a companion star, and therefore provides evidence that some Type Ia
supernovae arise from the single degenerate channel.Comment: Accepted for publication on the 21 May 2015 issue of Natur
Spectroscopic observations of sn 2012fr: A luminous, normal type ia supernova with early high-velocity features and a late velocity plateau
We present 65 optical spectra of the Type Ia SN 2012fr, 33 of which were obtained before maximum light. At early times, SN 2012fr shows clear evidence of a high-velocity feature (HVF) in the Si II λ6355 line that can be cleanly decoupled from the lower velocity photospheric component. This Si II λ6355 HVF fades by phase -5; subsequently, the photospheric component exhibits a very narrow velocity width and remains at a nearly constant velocity of 12,000 km s-1 until at least five weeks after maximum brightness. The Ca II infrared triplet exhibits similar evidence for both a photospheric component at v 12,000 km s-1 with narrow line width and long velocity plateau, as well as an HVF beginning at v 31,000 km s-1 two weeks before maximum. SN 2012fr resides on the border between the shallow silicon and core-normal subclasses in the Branch et al. classification scheme, and on the border between normal and high-velocity Type Ia supernovae (SNe Ia) in the Wang et al. system. Though it is a clear member of the low velocity gradient group of SNe Ia and exhibits a very slow light-curve decline, it shows key dissimilarities with the overluminous SN 1991T or SN 1999aa subclasses of SNe Ia. SN 2012fr represents a well-observed SN Ia at the luminous end of the normal SN Ia distribution and a key transitional event between nominal spectroscopic subclasses of SNe Ia. © 2013. The American Astronomical Society. All rights reserved.
European Red List of Marine Fishes
The European Red List is a review of the conservation
status of European species according to IUCN regional
Red Listing guidelines. It identifies those species that are
threatened with extinction at the regional level, so that
appropriate conservation action can be taken to improve
their status. This Red List publication summarises results
for all described native European marine fishes.Postprin
Pulmonary oxygen uptake and muscle deoxygenation kinetics during recovery in trained and untrained male adolescents
Previous studies have demonstrated faster pulmonary oxygen uptake ( V ˙ O 2 ) kinetics in the trained state during the transition to and from moderate-intensity exercise in adults. Whilst a similar effect of training status has previously been observed during the on-transition in adolescents, whether this is also observed during recovery from exercise is presently unknown. The aim of the present study was therefore to examine V ˙ O 2 kinetics in trained and untrained male adolescents during recovery from moderate-intensity exercise. 15 trained (15 ± 0.8 years, V ˙ O 2max 54.9 ± 6.4 mL kg−1 min−1) and 8 untrained (15 ± 0.5 years, V ˙ O 2max 44.0 ± 4.6 mL kg−1 min−1) male adolescents performed two 6-min exercise off-transitions to 10 W from a preceding “baseline” of exercise at a workload equivalent to 80% lactate threshold; V ˙ O 2 (breath-by-breath) and muscle deoxyhaemoglobin (near-infrared spectroscopy) were measured continuously. The time constant of the fundamental phase of V ˙ O 2 off-kinetics was not different between trained and untrained (trained 27.8 ± 5.9 s vs. untrained 28.9 ± 7.6 s, P = 0.71). However, the time constant (trained 17.0 ± 7.5 s vs. untrained 32 ± 11 s, P < 0.01) and mean response time (trained 24.2 ± 9.2 s vs. untrained 34 ± 13 s, P = 0.05) of muscle deoxyhaemoglobin off-kinetics was faster in the trained subjects compared to the untrained subjects. V ˙ O 2 kinetics was unaffected by training status; the faster muscle deoxyhaemoglobin kinetics in the trained subjects thus indicates slower blood flow kinetics during recovery from exercise compared to the untrained subjects
The Early Discovery of SN 2017ahn: Signatures of Persistent Interaction in a Fast-declining Type II Supernova
We present high-cadence, comprehensive data on the nearby (D 33 Mpc) Type II supernova (SN II) 2017ahn, discovered within about one day of the explosion, from the very early phases after explosion to the nebular phase. The observables of SN 2017ahn show a significant evolution over the 470 days of our follow-up campaign, first showing prominent, narrow Balmer lines and other high-ionization features purely in emission (i.e., flash spectroscopy features), which progressively fade and lead to a spectroscopic evolution similar to that of more canonical SNe II. Over the same period, the decline of the light curves in all bands is fast, resembling the photometric evolution of linearly declining H-rich core-collapse SNe. The modeling of the light curves and early flash spectra suggests that a complex circumstellar medium surrounds the progenitor star at the time of explosion, with a first dense shell produced during the very late stages of its evolution that is swept up by the rapidly expanding ejecta within the first similar to 6 days of the SN evolution, while signatures of interaction are observed also at later phases. Hydrodynamical models support the scenario in which linearly declining SNe II are predicted to arise from massive yellow super- or hypergiants depleted of most of their hydrogen layers
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