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 Physics , 2015, Abstract: The spectrum of a supernova results from a complex array of overlapping atomic signatures that are sensitive to the composition and state of unburned and freshly synthesized material. Most theoretical models indicate that observed features near 6000-6300 Angstroms in type I spectra are due to more than a single component of Si II l6355, if at all for poorly matched Ib, Ic, and super-luminous supernovae; an interpretation of Si II l6355 works for nominal 6150 Angstrom absorption features of all type Ia supernovae during the first month of free expansion while the same interpretation has not been successful for a majority of type Ib and Ic. Instead, canonical 6250 Angstrom absorption features of type Ib and Ic spectra are likely shaped primarily by faint signatures of Halpha. Meanwhile, we also find the identification of Si II l6355 in the spectra of broad-lined Ic and super-luminous events of type I/R is less convincing in spite of numerous model spectra used to show otherwise. Here we argue a more likely explanation for these 6000-6300 Angstrom features is that they are conspicuous signatures of blue-shifted absorption and emission in Halpha, which is observed for type II supernovae. Such a solution has yet to be investigated in detail for classically defined type I supernovae on account of historical mix-ups in supernova nomenclatures; type I means no hydrogen [sic]. Here we revisit line identifications of type I supernovae and briefly discuss implications for progenitor systems.
 Physics , 2010, DOI: 10.1088/0004-637X/718/2/957 Abstract: We present synthetic spectral fits of the typical Type Ib SN 1999dn and the Hydrogen Rich Ib SN 2000H using the generalized non-local thermodynamic equilibrium stellar atmospheres code \phx. We fit model spectra to five epochs of SN 1999dn ranging from ten days pre-maximum light to 17 days post-maximum light and the two earliest epochs of SN 2000H available, maximum light and six days post-maximum. Our goal is to investigate the possibility of hydrogen in Type Ib Supernovae (SNe Ib), specifically a feature around 6200\AA\ which has previously been attributed to high velocity H-alpha. In earlier work on SN 1999dn we found the most plausible alternative to H-alpha to be a blend of Si II and Fe II lines which can be adjusted to fit by increasing the metallicity. Our models are simple; they assume a powerlaw density profile with radius, homologous expansion, and solar compositions. The helium core is produced by burning 4H --> He in order to conserve nucleon number. For models with hydrogen the outer skin of the model consists of a shell of solar composition. The hydrogen mass of the standard solar composition shell is M_H less than about 0.001 times the mass of the sun in SN 1999dn and M_H less than about 0.2 times the mass of the sun for SN 2000H. Our models fit the observed spectra reasonably well, successfully reproducing most features including the characteristic He I absorptions. The hydrogen feature in SN 1999dn is clear, but much more pronounced in SN 2000H. We discuss a possible evolutionary scenario that accounts for the dichotomy in the hydrogen shell mass between these two supernovae.
 Physics , 2000, DOI: 10.1086/301352 Abstract: We present the first unambiguous detection of helium emission lines in spectra of Type Ic supernovae (SNe Ic). The presence of He I lines, with full width at half maximum ~ 2000 km/s, and the distinct absence of any other intermediate-width emission (e.g., Halpha), implies that the ejecta of SN Ic 1999cq are interacting with dense circumstellar material composed of almost pure helium. This strengthens the argument that the progenitors of SNe Ic are core-collapse events in stars that have lost both their hydrogen and helium envelopes, either through a dense wind or mass-transfer to a companion. In this way, SN 1999cq is similar to supernovae such as SN 1987K and SN 1993J that helped firmly establish a physical connection between Type Ib and Type II supernovae. The light curve of SN 1999cq is very fast, with an extremely rapid rise followed by a quick decline. SN 1999cq is also found to exhibit a high level of emission at blue wavelengths (< 5500 A), likely resulting from either an unusually large amount of iron and iron-group element emission or uncharacteristically low reddening compared with other SNe Ic.
 Sung-Chul Yoon Physics , 2015, DOI: 10.1017/pasa.2015.16 Abstract: Type Ib/c supernovae (SNe Ib/c) mark the deaths of hydrogen-deficient massive stars. The evolutionary scenarios for SNe Ib/c progenitors involve many important physical processes including mass loss by winds and its metallicity dependence, stellar rotation, and binary interactions. This makes SNe Ib/c an excellent test bed for stellar evolution theory. We review the main results of evolutionary models for SN Ib/c progenitors available in the literature and their confrontation with recent observations. We argue that the nature of SN Ib/c progenitors can be significantly different for single and binary systems, and that binary evolution models can explain the ejecta masses derived from SN Ib/c light curves, the distribution of SN Ib/c sites in their host galaxies, and the optical magnitudes of the tentative progenitor candidate of iPTF13bvn. We emphasize the importance of early-time observations of light curves and spectra, accurate measurements of helium mass in SN Ib/c ejecta, and systematic studies about the metallicity dependence of SN Ib/c properties, to better constrain theories.
 Physics , 2009, DOI: 10.1051/0004-6361/200811339 Abstract: We discuss the properties of the progenitors of core collapse SNe, as they can be deduced from rotating stellar models of single stars. The type of the SN progenitor was determined from the surface abundances at the pre-SN stage. The type of the SN event was obtained from the masses of hydrogen and helium ejected at the time of the core-collapse SN event. We find that the minimum amount of helium ejected by a core-collapse SN (of whatever type) is around 0.3 MSun. There is no difference between the WC and WO stars in the ejected masses of helium, CNO elements, and heavy elements. Also no difference is expected between the chemical composition of a WC star resulting from a normal or a homogeneous evolution. The progenitors of type Ib SNe are WNL, WNE, or less massive WC stars. Those of type Ic are WC and WO stars. WO stars are produced in a limited mass range (around 60 MSun) and only at low metallicity (for <= 0.010) as already found. The WO stars are the progenitors of only a small fraction of type Ic. Present stellar models indicate that, at solar metallicity, there is about 1 type Ib SN for 1 type Ic, and this ratio rises to 3 type Ic for 1 type Ib SN at twice solar metallicity. At this metallicity, type Ic's are more frequent than type Ib's because most massive stars that go through a WNE stage evolve further into a WC/WO phase. Current models can account for the observed number ratios SN Ib/SN II and SN Ic/SN II and for their observed variation with the metallicity. In case no supernova occurs when a black hole is formed, single-star models can still account for more than half of the observed (SN Ib+SN Ic)/SN II ratio for Z >= ZSun. For the GRB rate, our models produce too large a number for such an event, even if we restrict the progenitor to the WO stars.
 David Branch Physics , 2001, DOI: 10.1086/338127 Abstract: Synthetic spectra generated with the parameterized supernova synthetic-spectrum code SYNOW are compared to photospheric-phase spectra of Type Ib supernovae (SNe Ib). Although the synthetic spectra are based on many simplifying approximations, including spherical symmetry, they account well for the observed spectra. Our sample of SNe Ib obeys a tight relation between the velocity at the photosphere, as determined from the Fe II features, and the time relative to that of maximum light. From this we infer that the masses and the kinetic energies of the events in this sample were similar. After maximum light the minimum velocity at which the He I features form usually is higher than the velocity at the photosphere, but the minimum velocity of the ejected helium is at least as low as 7000 kms. Previously unpublished spectra of SN 2000H reveal the presence of hydrogen absorption features, and we conclude that hydrogen lines also were present in SNe 1999di and 1954A. Hydrogen appears to be present in SNe Ib in general, although in most events it becomes too weak to identify soon after maximum light. The hydrogen-line optical depths that we use to fit the spectra of SNe 2000H, 1999di, and 1954A are not high, so only a mild reduction in the hydrogen optical depths would be required to make these events look like typical SNe Ib. Similarly, the He I line optical depths are not very high, so a moderate reduction would make SNe Ib look like SNe Ic.
 Physics , 2010, DOI: 10.1111/j.1365-2966.2010.17186.x Abstract: Supernovae of Type IIb contain large fractions of helium and traces of hydrogen, which can be observed in the early and late spectra. Estimates of the hydrogen and helium mass and distribution are mainly based on early-time spectroscopy and are uncertain since the respective lines are usually observed in absorption. Constraining the mass and distribution of H and He is important to gain insight into the progenitor systems of these SNe. We implement a NLTE treatment of hydrogen and helium in a three-dimensional nebular code. Ionisation, recombination, (non-)thermal electron excitation and H$\alpha$ line scattering are taken into account to compute the formation of H$\alpha$, which is by far the strongest H line observed in the nebular spectra of SNe IIb. Other lines of H and He are also computed but are rarely identified in the nebular phase. Nebular models are computed for the Type IIb SNe 1993J, 2001ig, 2003bg and 2008ax as well as for SN 2007Y, which shows H$\alpha$ absorption features at early times and strong H$\alpha$ emission in its late phase, but has been classified as a SN Ib. We suggest to classify SN 2007Y as a SN IIb. Optical spectra exist for all SNe of our sample, and there is one IR nebular observation of SN 2008ax, which allows an exploration of its helium mass and distribution. We develop a three-dimensional model for SN 2008ax. We obtain estimates for the total mass and kinetic energy in good agreement with the results from light-curve modelling found in the literature. We further derive abundances of He, C, O, Ca and $^{56}$Ni. We demonstrate that H$\alpha$ absorption is probably responsible for the double-peaked profile of the [O {\sc i}] $\lambda\lambda$ 6300, 6363 doublet in several SNe IIb and present a mechanism alternative to shock interaction for generating late-time H$\alpha$ emission of SNe IIb.
 Physics , 2013, DOI: 10.1093/mnras/stt1303 Abstract: We present predictions for hydrogen and helium emission line luminosities from circumstellar matter around Type Ia supernovae (SNe Ia) using time dependent photoionization modeling. ESO/VLT optical echelle spectra of the SN Ia 2000cx were taken before and up to 70 days after maximum. We detect no hydrogen and helium lines, and place an upper limit on the mass loss rate for the putative wind of less than 1.3EE{-5} solar masses per year, assuming a speed of 10 km/s and solar abundances for the wind. In a helium-enriched case, the best line to constrain the mass loss would be He I 10,830 A. We confirm the details of interstellar Na I and Ca II absorption towards SN 2000cx as discussed by Patat et al., but also find evidence for 6613.56 A Diffuse Interstellar Band (DIB) absorption in the Milky Way. We discuss measurements of the X-ray emission from the interaction between the supernova ejecta and the wind and we re-evaluate observations of SN 1992A obtained 16 days after maximum by Schlegel & Petre. We find an upper limit of 1.3EE{-5} solar masses per year. These results, together with the previous observational work on the normal SNe Ia 1994D and 2001el, disfavour a symbiotic star in the upper mass loss rate regime from being the likely progenitor scenario for these SNe. To constrain hydrogen in late time spectra, we present ESO/VLT and ESO/NTT optical and infrared observations of SNe Ia 1998bu and 2000cx 251-388 days after maximum. We see no hydrogen line emission in SNe 1998bu and 2000cx at these epochs, and we argue from modeling that the mass of such hydrogen-rich gas must be less than 0.03 solar masses for both supernovae. Comparing similar upper limits with recent models of Pan et al., it seems hydrogen-rich donors with a separation of less than 5 times the radius of the donor may be ruled out for the five SNe Ia 1998bu, 2000cx, 2001el, 2005am and 2005cf.
 Physics , 2014, DOI: 10.1093/mnras/stv650 Abstract: The shape of the light curve peak of radioactive--powered core--collapse "stripped--envelope" supernovae constrains the ejecta mass, nickel mass, and kinetic energy by the brightness and diffusion time for a given opacity and observed expansion velocity. Late--time light curves give constraints on the ejecta mass and energy, given the gamma--ray opacity. Previous work has shown that the principal light curve peaks for SN~IIb with small amounts of hydrogen and for hydrogen/helium--deficient SN~Ib/c are often rather similar near maximum light, suggesting similar ejecta masses and kinetic energies, but that late--time light curves show a wide dispersion, suggesting a dispersion in ejecta masses and kinetic energies. It was also shown that SN~IIb and SN~Ib/c can have very similar late--time light curves, but different ejecta velocities demanding significantly different ejecta masses and kinetic energies. We revisit these topics by collecting and analyzing well--sampled single--band and quasi--bolometric light curves from the literature. We find that the late--time light curves of stripped--envelope core--collapse supernovae are heterogeneous. We also show that the observed properties, the photospheric velocity at peak, the rise time, and the late decay time, can be used to determine the mean opacity appropriate to the peak. The opacity determined in this way is considerably smaller than common estimates. We discuss how the small effective opacity may result from recombination and asymmetries in the ejecta.
 Physics , 2001, DOI: 10.1086/319390 Abstract: We present 84 spectra of Type Ib/c and Type IIb supernovae (SNe), describing the individual SNe in detail. The relative depths of the helium absorption lines in the spectra of the SNe Ib appear to provide a measurement of the temporal evolution of the SN, with He I 5876 and He I 7065 growing in strength relative to He I 6678 over time. Light curves for three of the SNe Ib provide a sequence for correlating the helium-line strengths. We find that some SNe Ic show evidence for weak helium absorption, but most do not. Aside from the presence or absence of the helium lines, there are other spectroscopic differences between SNe Ib and SNe Ic. On average, the O I 7774 line is stronger in SNe Ic than in SNe Ib. In addition, the SNe Ic have distinctly broader emission lines at late times, indicating either a consistently larger explosion energy and/or lower envelope mass for SNe Ic than for SNe Ib. While SNe Ib appear to be basically homogeneous, the SNe Ic are quite heterogeneous in their spectroscopic characteristics. Three SNe Ic that may have been associated with gamma-ray bursts are also discussed; two of these have clearly peculiar spectra, while the third seems fairly typical.
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