678 research outputs found
Type II-Plateau supernova radiation: dependencies on progenitor and explosion properties
We explore the properties of Type II-Plateau (II-P) supernovae (SNe) together
with their red-supergiant (RSG) star progenitors. Using MESA STAR, we modulate
the parameters (e.g., mixing length, overshoot, rotation, metallicity) that
control the evolution of a 15Msun main-sequence star to produce a variety of
physical pre-SN models and SN II-P ejecta. We extend previous modeling of SN
II-P radiation to include photospheric and nebular phases, as well as
multi-band light curves and spectra. Our treatment does not assume local
thermodynamic equilibrium, is time dependent, treats explicitly the effects of
line blanketing, and incorporates non-thermal processes. We find that the color
properties of SNe II-P require large model atoms for FeI and FeII, much larger
than adopted in Dessart & Hillier (2011). The color properties also imply RSG
progenitors of limited extent (~500Rsun) --- larger progenitor stars produce a
SN II-P radiation that remains too blue for too long. This finding calls for a
reduction of RSG radii, perhaps through a strengthening of convective energy
transport in RSG envelopes. Increased overshoot and rotation reduce the ratio
of ejecta to helium-core mass, similarly to an increase in main-sequence mass,
and thus complicate the inference ofprogenitor masses. In contrast to the great
sensitivity on progenitor radius, SN II-P color evolution appears insensitive
to variations in explosion energy. Finally, we document the numerous SN II-P
signatures that vary with progenitor metallicity, revealing their potential for
metallicity determinations in the nearby and distant Universe.Comment: Paper accepted to MNRA
Radiative Properties of Pair-instability Supernova Explosions
We present non-LTE time-dependent radiative-transfer simulations of
pair-instability supernovae (PISNe) stemming from red-supergiant (RSG),
blue-supergiant (BSG) and Wolf-Rayet (WR) star rotation-free progenitors born
in the mass range 160-230Msun, at 10^-4 Zsun. Although subject to uncertainties
in convection and stellar mass-loss rates, our initial conditions come from
physically-consistent models that treat evolution from the main-sequence, the
onset of the pair-production instability, and the explosion phase. With our set
of input models characterized by large 56Ni and ejecta masses, and large
kinetic energies, we recover qualitatively the Type II-Plateau, II-peculiar,
and Ib/c light-curve morphologies, although they have larger peak bolometric
luminosities (~10^9 to 10^10 Lsun) and a longer duration (~200d). We discuss
the spectral properties for each model during the photospheric and nebular
phases, including Balmer lines in II-P and II-pec at early times, the dominance
of lines from intermediate-mass-elements (IMEs) near the bolometric maximum,
and the strengthening of metal line blanketing thereafter. Having similar
He-core properties, all models exhibit similar post-peak spectra that are
strongly blanketed by FeII and FeI lines, characterized by red colors, and that
arise from photospheres/ejecta with a temperature of <4000K. Combined with the
modest line widths after bolometric peak, these properties contrast with those
of known super-luminous SNe suggesting that PISNe are yet to be discovered.
Being reddish, PISNe will be difficult to observe at high redshift except when
they stem from RSG explosions, in which case they could be used as metallicity
probes and distance indicators.Comment: accepted to MNRA
Radiative-transfer models for explosions from rotating and non-rotating single WC stars. Implications for SN1998bw and LGRB/SNe
Using 1-D non-Local-Thermodynamic-Equilibrium time-dependent
radiative-transfer simulations, we study the ejecta properties required to
match the early and late-time photometric and spectroscopic properties of
supernovae (SNe) associated with long-duration gamma-ray bursts (LGRBs). To
match the short rise time, narrow light curve peak, and extremely broad
spectral lines of SN1998bw requires a model with <3Msun ejecta but a high
explosion energy of a few 1e52erg and 0.5Msun of Ni56. However the relatively
high luminosity, the presence of narrow spectral lines of intermediate mass
elements, and the low ionization at the nebular stage are matched with a more
standard C-rich Wolf-Rayet (WR) star explosion, with an ejecta of >10Msun, an
explosion energy >1e51erg, and only 0.1Msun of Ni56. As the two models are
mutually exclusive, the breaking of spherical symmetry is essential to match
the early/late photometric/spectroscopic properties of SN1998bw. This
conclusion confirms the notion that the ejecta of SN1998bw is aspherical on
large scales. More generally, with asphericity, the energetics and Ni56 mass of
LGRB/SNe are reduced and their ejecta mass is increased, favoring a massive
fast-rotating Wolf-Rayet star progenitor. Contrary to persisting claims in
favor of the proto-magnetar model for LGRB/SNe, such progenitor/ejecta
properties are compatible with collapsar formation. Ejecta properties of
LGRB/SNe inferred from 1D radiative-transfer modeling are fundamentally flawed.Comment: Submitted to A&
Radiative-transfer models for supernovae IIb/Ib/Ic from binary-star progenitors
We present 1-D non-Local-Thermodynamic-Equilibrium time-dependent
radiative-transfer simulations for supernovae (SNe) of type IIb, Ib, and Ic
that result from the terminal explosion of the mass donor in a close-binary
system. Here, we select three ejecta with a total kinetic energy of ~1.2e51erg,
but characterised by different ejecta masses (2-5Msun), composition, and
chemical mixing. The type IIb/Ib models correspond to the progenitors that have
retained their He-rich shell at the time of explosion. The type Ic model arises
from a progenitor that has lost its helium shell, but retains 0.32Msun of
helium in a CO-rich core of 5.11Msun. We discuss their photometric and
spectroscopic properties during the first 2-3 months after explosion, and
connect these to their progenitor and ejecta properties including chemical
stratification. For these three models, Arnett's rule overestimates the 56Ni
mass by ~50% while the procedure of Katz et al., based on an energy argument,
yields a more reliable estimate. The presence of strong CI lines around 9000A
prior to maximum is an indicator that the pre-SN star was under-abundant in
helium. As noted by others, the 1.08micron feature is a complex blend of CI,
MgII, and HeI lines, which makes the identification of He uncertain in SNe Ibc
unless other HeI lines can be identified. Our models show little scatter in
(V-R) colour 10d after R-band maximum. We also address a number of radiative
transfer properties of SNe Ibc, including the notion of a photosphere, the
inference of a representative ejecta expansion rate, spectrum formation,
blackbody fits and "correction factors".Comment: accepted to MNRA
Inferring supernova IIb/Ib/Ic ejecta properties from light curves and spectra: Correlations from radiative-transfer models
We present 1-D non-Local-Thermodynamic-Equilibrium time-dependent
radiative-transfer simulations for a large grid of supernovae (SNe) IIb/Ib/Ic
that result from the terminal explosion of the mass donor in a close-binary
system. Our sample covers ejecta masses of 1.75.2M,
kinetic energies of 0.65.010erg, and Ni
masses of 0.050.30M. We find a strong correlation between the
Ni mass and the photometric properties at maximum, and between the rise
time to bolometric maximum and the post-maximum decline rate. We confirm the
small scatter in () at 10d past -band maximum. The quantity is comparable to the Doppler velocity
measured from HeI 5875\AA\ at maximum in SNe IIb/Ib, although some scatter
arises from the uncertain level of chemical mixing. The OI7772\AA\ line may be
used for SNe Ic, but the correspondence deteriorates with higher ejecta
mass/energy. We identify a temporal reversal of the Doppler velocity at maximum
absorption in the 1.05m feature in all models. The reversal is due
to HeI alone and could serve as a test for the presence of helium in SNe Ic.
Because of variations in composition and ionisation, the ejecta opacity shows
substantial variations with both velocity and time. This is in part the origin
of the offset between our model light curves and the predictions from the
Arnett model.Comment: Accepted for publication in the MNRA
GUCY2C maintains intestinal LGR5+ stem cells by opposing ER stress
Long-lived multipotent stem cells (ISCs) at the base of intestinal crypts adjust their phenotypes to accommodate normal maintenance and post-injury regeneration of the epithelium. Their long life, lineage plasticity, and proliferative potential underlie the necessity for tight homeostatic regulation of the ISC compartment. In that context, the guanylate cyclase C (GUCY2C) receptor and its paracrine ligands regulate intestinal epithelial homeostasis, including proliferation, lineage commitment, and DNA damage repair. However, a role for this axis in maintaining ISCs remains unknown. Transgenic mice enabling analysis of ISCs (Lgr5-GFP) in the context of GUCY2C elimination (Gucy2c-/-) were combined with immunodetection techniques and pharmacological treatments to define the role of the GUCY2C signaling axis in supporting ISCs. ISCs were reduced in Gucy2c-/- mice, associated with loss of active Lgr5+ cells but a reciprocal increase in reserve Bmi1+ cells. GUCY2C was expressed in crypt base Lgr5+ cells in which it mediates canonical cyclic (c) GMPdependent signaling. Endoplasmic reticulum (ER) stress, typically absent from ISCs, was elevated throughout the crypt base in Gucy2c-/- mice. The chemical chaperone tauroursodeoxycholic acid resolved this ER stress and restored the balance of ISCs, an effect mimicked by the GUCY2C effector 8Br-cGMP. Reduced ISCs in Gucy2c-/-mice was associated with greater epithelial injury and impaired regeneration following sub-lethal doses of irradiation. These observations suggest that GUCY2C provides homeostatic signals that modulate ER stress and cell vulnerability as part of the machinery contributing to the integrity of ISCs. © Kraft et al
The pharmacokinetics of nebulized nanocrystal budesonide suspension in healthy volunteers.
Nanocrystal budesonide (nanobudesonide) is a suspension for nebulization in patients with steroid-responsive pulmonary diseases such as asthma. The pharmacokinetics and safety of the product were compared to those of Pulmicort Respules. Sixteen healthy volunteers were administered nanobudesonide 0.5 and 1.0 mg, Pulmicort Respules 0.5 mg, and placebo in a four-way, randomized crossover design. All nebulized formulations were well tolerated, with no evidence of bronchospasm. Nebulization times were significantly shorter for nanobudesonide compared to Pulmicort Respules. Because of a low oral bioavailability, plasma concentration of budesonide is a good marker of lung-delivered dose. The pharmacokinetics of nanobudesonide 0.5 and 1.0 mg were approximately dose proportional with respect to Cmax, AUC(0-t), and AUC(0-infinity). Nanobudesonide 0.5 mg and Pulmicort Respules 0.5 mg exhibited similar AUCs, suggesting a similar extent of pulmonary absorption. A higher Cmax was noted with nanobudesonide 0.5 mg, and the tmax was significantly different, suggesting a more rapid rate of drug delivery of nanobudesonide 0.5 mg than Pulmicort Respules. In conclusion, nebulized nanobudesonide 0.5 mg was safe in healthy volunteers, with a similar extent of absorption as Pulmicort Respules
History Literacy and Visual Informational Texts: Scrutinizing Photographs Beyond their Borders
State and national initiatives prescribe, among other things, increases in students’ reading of informational texts and uses of diverse literacies. History educators must purposefully integrate informational texts with literacy strategies that facilitate historical thinking. Students are to analyze and scrutinize, not simply read or view. This paper refines previously suggested photograph analysis methods to consider a photographer’s influence both within and beyond the photograph’s borders. Our modification centers on the diverse, and hitherto unexplored, ways in which the photographer influences the viewer’s understanding of the photograph and the historical event that is captured. We offer informational texts and discipline-appropriate methods as ancillaries
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