ABSTRACT Supernovae (SNe) embedded in dense circumstellar material (CSM) may show prominent emission lines in their early-time spectra (≤10 days after the explosion), owing to recombination of the ...CSM ionized by the shock-breakout flash. From such spectra ("flash spectroscopy"), we can measure various physical properties of the CSM, as well as the mass-loss rate of the progenitor during the year prior to its explosion. Searching through the Palomar Transient Factory (PTF and iPTF) SN spectroscopy databases from 2009 through 2014, we found 12 SNe II showing flash-ionized (FI) signatures in their first spectra. All are younger than 10 days. These events constitute 14% of all 84 SNe in our sample having a spectrum within 10 days from explosion, and 18% of SNe II observed at ages <5 days, thereby setting lower limits on the fraction of FI events. We classified as "blue/featureless" (BF) those events having a first spectrum that is similar to that of a blackbody, without any emission or absorption signatures. It is possible that some BF events had FI signatures at an earlier phase than observed, or that they lack dense CSM around the progenitor. Within 2 days after explosion, 8 out of 11 SNe in our sample are either BF events or show FI signatures. Interestingly, we found that 19 out of 21 SNe brighter than an absolute magnitude MR = −18.2 belong to the FI or BF groups, and that all FI events peaked above MR = −17.6 mag, significantly brighter than average SNe II.
With the advent of new wide-field, high-cadence optical transient surveys, our understanding of the diversity of core-collapse supernovae has grown tremendously in the last decade. However, the ...pre-supernova evolution of massive stars, which sets the physical backdrop to these violent events, is theoretically not well understood and difficult to probe observationally. Here we report the discovery of the supernova iPTF 13dqy = SN 2013fs a mere ∼3 h after explosion. Our rapid follow-up observations, which include multiwavelength photometry and extremely early (beginning at ∼6 h post-explosion) spectra, map the distribution of material in the immediate environment (<, ~1015 cm) of the exploding star and establish that it was surrounded by circumstellar material (CSM) that was ejected during the final ∼1 yr prior to explosion at a high rate, around 10-3 solar masses per year. The complete disappearance of flash-ionized emission lines within the first several days requires that the dense CSM be confined to within <, ~1015 cm, consistent with radio non-detections at 70-100 days. The observations indicate that iPTF 13dqy was a regular type II supernova; thus, the finding that the probable red supergiant progenitor of this common explosion ejected material at a highly elevated rate just prior to its demise suggests that pre-supernova instabilities may be common among exploding massive stars.
Abstract
We present observations of two new hydrogen-poor superluminous supernovae (SLSN-I), iPTF15esb and iPTF16bad, showing late-time H
α
emission with line luminosities of
erg s
−1
and velocity ...widths of (4000–6000) km s
−1
. Including the previously published iPTF13ehe, this makes up a total of three such events to date. iPTF13ehe is one of the most luminous and the slowest evolving SLSNe-I, whereas the other two are less luminous and fast decliners. We interpret this as a result of the ejecta running into a neutral H-shell located at a radius of ∼10
16
cm. This implies that violent mass loss must have occurred several decades before the supernova explosion. Such a short time interval suggests that eruptive mass loss could be common shortly before core collapse, and more importantly helium is unlikely to be completely stripped off the progenitor and could be present in the ejecta. It is a mystery why helium features are not detected, even though nonthermal energy sources, capable of ionizing He, may exist as suggested by the O
ii
absorption series in the early-time spectra. Our late-time spectra (+240 days) appear to have intrinsically lower O
i
6300 Å luminosities than that of SN2015bn and SN2007bi, which is possibly an indication of less oxygen (<10
M
⊙
). The blueshifted H
α
emission relative to the hosts for all three events may be in tension with the binary model proposed for iPTF13ehe. Finally, iPTF15esb has a peculiar light curve (LC) with three peaks separated from one another by ∼22 days. The LC undulation is stronger in bluer bands. One possible explanation is ejecta-circumstellar medium interaction.
Modern wide-field, optical time-domain surveys must solve a basic optimization problem: maximize the number of transient discoveries or minimize the follow-up needed for the new discoveries. Here, we ...describe the Color Me Intrigued experiment, the first from the intermediate Palomar Transient Factory (iPTF) to search for transients simultaneously in the gPTF and RPTF bands. During the course of this experiment, we discovered iPTF 16fnm, a new member of the 02cx-like subclass of Type Ia supernovae (SNe). iPTF 16fnm peaked at , making it the second-least-luminous known SN Ia. iPTF 16fnm exhibits all the hallmarks of the 02cx-like class: (i) low luminosity at peak, (ii) low ejecta velocities, and (iii) a non-nebular spectrum several months after peak. Spectroscopically, iPTF 16fnm exhibits a striking resemblance to two other low-luminosity 02cx-like SNe: SN 2007qd and SN 2010ae. iPTF 16fnm and SN 2005hk decline at nearly the same rate, despite a 3 mag difference in brightness at peak. When considering the full subclass of 02cx-like SNe, we do not find evidence for a tight correlation between peak luminosity and decline rate in either the g′ or r′ band. We measure the relative rate of 02cx-like SNe to normal SNe Ia and find . We further examine the g′ − r′ evolution of 02cx-like SNe and find that their unique color evolution can be used to separate them from 91bg-like and normal SNe Ia. This selection function will be especially important in the spectroscopically incomplete Zwicky Transient Facility/Large Synoptic Survey Telescope (LSST) era. Finally, we close by recommending that LSST periodically evaluate, and possibly update, its observing cadence to maximize transient science.
Copper-based dilute Cu–Cr–Zr alloys and their minor modifications, because of their excellent thermal conductivity, strength and fatigue resistance, are commonly used in an aged condition in heat ...transfer elements. However, in comparison to dilute Cu–Cr binary alloys in which the precipitation of chromium has been studied extensively in the last two decades, attempts at delineating the morphology, composition and crystallography of precipitates in Cu–Cr–Zr alloys have been few and only partially successful. The role of zirconium has also remained largely unresolved. In the present work, the precipitation in an alloy having a nominal composition of Cu–1 wt% Cr–0.1 wt% Zr has been shown to take place through the formation of a metastable ordered fcc phase. Also, the improvement in fatigue resistance due to the addition of zirconium has been ascribed to lowering of the stacking fault energy (SFE) of the alloy.
We investigate ZTF18aalrxas, a double-peaked Type IIb core-collapse supernova (SN) discovered during science validation of the Zwicky Transient Facility. ZTF18aalrxas was discovered while the optical ...emission was still rising toward the initial cooling peak (0.7 mag over 2 days). Our observations consist of multi-band (ultraviolet and optical) light curves (LCs), and optical spectra spanning from 0.7 to 180 days past the explosion. We use a Monte-Carlo based non-local thermodynamic equilibrium model that simultaneously reproduces both the 56Ni-powered bolometric LC and our nebular spectrum. This model is used to constrain the synthesized radioactive nickel mass (0.17 M☉) and the total ejecta mass (1.7 M☉) of the SN. The cooling emission is modeled using semi-analytical extended envelope models to constrain the progenitor radius (790-1050 R ) at the time of explosion. Our nebular spectrum shows signs of interaction with a dense circumstellar medium (CSM), and this spectrum is modeled and analyzed to constrain the amount of ejected oxygen (0.3-0.5 M☉) and the total hydrogen mass ( 0.15 M☉) in the envelope of the progenitor. The oxygen mass of ZTF18aalrxas is consistent with a low (12-13 M☉) zero-age main-sequence mass progenitor. The LCs and spectra of ZTF18aalrxas are not consistent with massive single-star SN Type IIb progenitor models. The presence of an extended hydrogen envelope of low mass, the presence of a dense CSM, the derived ejecta mass, and the late-time oxygen emission can all be explained in a binary model scenario.
Precipitation in a Cu–Cr–Zr alloy Batra, I.S.; Dey, G.K.; Kulkarni, U.D. ...
Materials science & engineering. A, Structural materials : properties, microstructure and processing,
09/2003, Letnik:
356, Številka:
1
Journal Article
Recenzirano
Transmission electron microscopy (TEM) investigations of the early stages of precipitation of a b.c.c. phase in f.c.c. matrix have been carried out in a dilute Cu–Cr–Zr alloy. The initial product of ...decomposition, characterized by a state of order, which mimics a cube-on-cube orientation relationship (OR) with the matrix appears prior to ordered b.c.c. phase precipitates showing Nishiyama–Wassermann (N–W) OR.
► A methodology was proposed to predict amorphous forming compositions (AFCs). ► Chemical contribution to enthalpy of mixing∝enthalpy of amorphous for AFCs. ► Accuracy in the prediction of AFC-range ...was noticed in Al–Ni–Ti system. ► Mechanical alloying (MA) results of Al–Ni–Ti followed the predicted AFC-range. ► Earlier MA results of Al–Ni–Ti also conformed to the predicted AFC-range.
From the earlier works on the prediction of amorphous forming composition range (AFCR) using Miedema based model and also, on mechanical alloying experiments it has been observed that all amorphous forming compositions of a given alloy system falls within a linear band when the chemical contribution to enthalpy of the solid solution (ΔHss) is plotted against the enthalpy of mixing in the amorphous phase (ΔHamor). On the basis of this observation, a methodology has been proposed in this article to identify the AFCR of a ternary system that is likely to be more precise than what can be obtained using ΔHamor−ΔHss<0 criterion. MA experiments on various compositions of Al–Ni–Ti system, producing amorphous, crystalline, and mixture of amorphous plus crystalline phases have been carried out and the phases have been characterized using X-ray diffraction and transmission electron microscopy techniques. Data from the present MA experiments and, also, from the literature have been used to validate the proposed approach. Also, the proximity of compositions, producing a mixture of amorphous and crystalline phases to the boundary of AFCR in the Al–Ni–Ti ternary has been found useful to validate the effectiveness of the prediction.
Industrial emissions are a serious environmental problem worldwide due to particulates and toxic gases. This study aims to generate an activity-specific emission inventory and estimate emissions ...dispersion extent in the vicinity of the coastal industrial village by simulating the existing coke oven and pellet plant emissions using the steady-state plume model. Continuous air quality monitoring results were compared with the predicted consequential emissions for the year 2018-19. The maximum ground-level concentrations of particulate and gases within the modeling simulation domain were observed at 9005 m away from the center. They were predicted to be 116.39 μg.m-3, 79.14 μg.m-3, 52.97 μg.m-3, and 211.86 μg.m-3. Data analysis showed that air mass transport from the project to the receptor sites resulted in ambient air concentrations higher than those observed in the other sites. Overall predicted results obtained from AERMOD Cloud simulations were shown to have less bias than the measured results. They recommended considering it as appropriate for the prediction of annual average concentration.
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