We present 1D non-local thermodynamic equilibrium time-dependent radiative transfer simulations of a Chandrasekhar-mass delayed-detonation model which synthesizes 0.51 M⊙ of 56Ni, and confront our ...results to the Type Ia supernova (SN Ia) 2002bo over the first 100 d of its evolution. Assuming only homologous expansion, this same model reproduces the bolometric and multiband light curves, the secondary near-infrared (NIR) maxima, and the optical and NIR spectra. The chemical stratification of our model qualitatively agrees with previous inferences by Stehle et al., but reveals significant quantitative differences for both iron-group and intermediate-mass elements. We show that ±0.1 M⊙ (i.e. ±20 per cent) variations in 56Ni mass have a modest impact on the bolometric and colour evolution of our model. One notable exception is the U band, where a larger abundance of iron-group elements results in less opaque ejecta through ionization effects, our model with more 56Ni displaying a higher near-ultraviolet flux level. In the NIR range, such variations in 56Ni mass affect the timing of the secondary maxima but not their magnitude, in agreement with observational results. Moreover, the variation in the I, J, and K
s magnitudes is less than 0.1 mag within ∼10 d from bolometric maximum, confirming the potential of NIR photometry of SNe Ia for cosmology. Overall, the delayed-detonation mechanism in single Chandrasekhar-mass white dwarf progenitors seems well suited for SN 2002bo and similar SNe Ia displaying a broad Si ii 6355 Å line. Whatever multidimensional processes are at play during the explosion leading to these events, they must conspire to produce an ejecta comparable to our spherically symmetric model.
We present 1D 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 ≈1.2 × 1051 erg, but characterized by different ejecta masses (2–5 M⊙), 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 0.32 M⊙ of helium in a CO-rich core of 5.11 M⊙. 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 per cent while the procedure of Katz et al., based on an energy argument, yields a more reliable estimate. The presence of strong C i lines around 9000Å prior to maximum is an indicator that the pre-SN star was underabundant in helium. As noted by others, the 1.08μm feature is a complex blend of C i, Mg ii, and He i lines, which makes the identification of He uncertain in SNe Ibc unless other He i lines can be identified. Our models show little scatter in (V − R) colour 10 d 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’.
Infrared observations of the dusty, massive Homunculus Nebula around the luminous blue variable
Carinae are crucial to characterize the mass-loss history and help constrain the mechanisms leading to ...the Great Eruption. We present the 2.4 - 670
m spectral energy distribution, constructed from legacy ISO observations and new spectroscopy obtained with the
Using radiative transfer modeling, we find that the two best-fit dust models yield compositions which are consistent with CNO-processed material, with iron, pyroxene and other metal-rich silicates, corundum, and magnesium-iron sulfide in common. Spherical corundum grains are supported by the good match to a narrow 20.2
m feature. Our preferred model contains nitrides AlN and Si
N
in low abundances. Dust masses range from 0.25 to 0.44
but
≥ 45
in both cases due to an expected high Fe gas-to-dust ratio. The bulk of dust is within a 5″ × 7″ central region. An additional compact feature is detected at 390
m. We obtain
= 2.96 × 10
, a 25% decline from an average of mid-IR photometric levels observed in 1971-1977. This indicates a reduction in circumstellar extinction in conjunction with an increase in visual brightness, allowing 25-40% of optical and UV radiation to escape from the central source. We also present an analysis of
CO and
CO
= 5 - 4 through 9 - 8 lines, showing that the abundances are consistent with expectations for CNO-processed material. The
C II line is detected in absorption, which we suspect originates in foreground material at very low excitation temperatures.
ABSTRACT
We present a new relativistic radiative transfer code for γ-rays of energy less than 5 MeV in supernova (SN) ejecta. This code computes the opacities, the prompt emissivity (i.e. decay), and ...the scattering emissivity, and solves for the intensity in the co-moving frame. Because of the large expansion velocities of SN ejecta, we ignore redistribution effects associated with thermal motions. The energy deposition is calculated from the energy removed from the radiation field by scattering or photoelectric absorption. This new code yields comparable results to an independent Monte Carlo code. However, both yield non-trivial differences with the results from a pure absorption treatment of γ-ray transport. A synthetic observer’s frame spectrum is also produced from the co-moving frame intensity. At early times when the optical depth to γ-rays is large, the synthetic spectrum shows asymmetric line profiles with redshifted absorption as seen in SN 2014J. This new code is integrated within cmfgen and allows for an accurate and fast computation of the decay energy deposition in SN ejecta.
We present a multi-epoch quantitative spectroscopic analysis of the Type IIn supernova (Type IIn SN) 1994W, an event interpreted by Chugai et al. as stemming from the interaction between the ejecta ...of a SN and a 0.4 M⊙ circumstellar shell ejected 1.5 yr before core collapse. During the brightening phase, our models suggest that the source of optical radiation is not unique, perhaps associated with an inner optically thick cold dense shell and outer optically thin shocked material. During the fading phase, our models support a single source of radiation, an hydrogen-rich optically thick layer with a near-constant temperature of ∼7000 K that recedes from a radius of 4.3 × 1015 at a peak to 2.3 × 1015 cm 40 d later. We reproduce the hybrid narrow-core broad-wing line profile shapes of SN 1994W at all times, invoking an optically thick photosphere exclusively (i.e. without any external optically thick shell). In SN 1994W, slow expansion makes scattering with thermal electrons a key escape mechanism for photons trapped in optically thick line cores, and allows the resulting broad incoherent electron-scattering wings to be seen around narrow-line cores. In SNe with larger expansion velocities, the thermal broadening due to incoherent scattering is masked by the broad profile and the dominant frequency redshift occasioned by bulk motions. Given the absence of broad lines at all times and the very low 56Ni yields, we speculate whether SN 1994W could have resulted from an interaction between two ejected shells without core collapse. The high conversion efficiency of kinetic to thermal energy may not require a SN-like energy budget for SN1994W.
Non‐thermal excitation and ionization in supernovae Li, Chengdong; Hillier, D. John; Dessart, Luc
Monthly Notices of the Royal Astronomical Society,
21 October 2012, Letnik:
426, Številka:
2
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
We incorporate non‐thermal excitation and ionization processes arising from non‐thermal electrons that result from γ‐ray energy deposition into our radiative transfer code cmfgen. The ...non‐thermal electron distribution is obtained by solving the Spencer–Fano equation using the procedure of Kozma & Fransson. We applied the non‐thermal calculations to the blue supergiant explosion model whose early evolution was studied in Dessart & Hillier. Non‐thermal processes generally increase excitation and ionization and decrease the temperature of the ejecta. We confirm that non‐thermal processes are crucial for modelling nebular spectra. Both optical H i and He i lines are significantly strengthened. While optical He i lines are not easily discerned in observational spectra due to severe blending with other lines, He i 2.058 μm provides an excellent opportunity to infer the influence of non‐thermal processes. We also discuss the processes controlling the formation of He i lines during nebular epochs. Most lines of other species are only slightly affected. We also show that the inclusion of Fe i has substantial line‐blanketing effects on optical spectra. Our model spectra and synthetic light curves are compared to the observations of SN 1987A. The spectral evolution shows broad agreement with the observations, especially Hα. The uncertainties of the non‐thermal solver are studied, and are expected to be small. With this new addition of non‐thermal effects in cmfgen, we now treat all known important processes controlling the radiative transfer of supernova ejecta, whatever the type and the epoch.
In previous papers we discussed results from fully time-dependent radiative transfer models for core-collapse supernova (SN) ejecta, including the Type II-peculiar SN 1987A, the more 'generic' SN ...II-Plateau, and more recently Type IIb/Ib/Ic SNe. Here we describe the modifications to our radiative modelling code, cmfgen, which allowed those studies to be undertaken. The changes allow for time-dependent radiative transfer of SN ejecta in homologous expansion. In the modelling we treat the entire SN ejecta, from the innermost layer that does not fall back on the compact remnant out to the progenitor surface layers. From our non-local thermodynamic equilibrium time-dependent line-blanketed synthetic spectra, we compute the bolometric and multiband light curves: light curves and spectra are thus calculated simultaneously using the same physical processes and numerics. These upgrades, in conjunction with our previous modifications which allow the solution of the time-dependent rate equations, will improve the modelling of SN spectra and light curves, and hence facilitate new insights into SN ejecta properties, the SN progenitors and the explosion mechanisms. cmfgen can now be applied to the modelling of all SN types.
The model atmosphere programs FASTWIND and CMFGEN are both elegantly designed to perform non-LTE analyses of the spectra of hot massive stars, and include sphericity and mass-loss. The two codes ...differ primarily in their approach toward line blanketing, with CMFGEN treating all of the lines in the co-moving frame and FASTWIND taking an approximate approach which speeds up execution times considerably. Although both have been extensively used to model the spectra of O-type stars, no studies have used the codes to independently model the same spectra of the same stars and compare the derived physical properties. We perform this task on 10 O-type stars in the Magellanic Clouds. For the late-type O supergiants, both CMFGEN and FASTWIND have trouble fitting some of the He I lines, and we discuss causes and cures. We find that there is no difference in the average effective temperatures found by the two codes for the stars in our sample, although the dispersion is large, due primarily to the various difficulties each code has with He I. The surface gravities determined using FASTWIND are systematically lower by 0.12 dex compared to CMFGEN, a result we attribute to the better treatment of electron scattering by CMFGEN. This has implications for the interpretation of the origin of the so-called mass discrepancy, as the masses derived by FASTWIND are on average lower than inferred from stellar evolutionary models, while those found by CMFGEN are in better agreement.
Abstract
Previous Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph (STIS) longslit observations of Eta Carinae (
η
Car) identified numerous absorption features in both the stellar ...spectrum, and in the adjacent nebular spectra, along our line of sight (LOS). The absorption features became temporarily stronger when the ionizing far-ultraviolet radiation field was reduced by the periastron passage of the secondary star. Subsequently, dissipation of a dusty structure in our LOS has led to a long-term increase in the apparent brightness of
η
Car, an increase in the ionizing ultraviolet (UV) radiation, and the disappearance of absorption from multiple velocity-separated shells extending across the foreground Homunculus lobe. We use HST/STIS spectro-images, coupled with published infrared and radio observations, to locate this intervening dusty structure. The velocity and spatial information indicate the occulter is ≈1000 au in front of
η
Car. The Homunculus is a transient structure composed of dusty, partially ionized ejecta that eventually will disappear due to the relentless rain of ionizing radiation and wind from the current binary system along with dissipation and mixing with the interstellar medium. This evolving complex continues to provide an astrophysical laboratory that changes on human timescales.
We present VLT–FORS spectropolarimetric observations of the type II supernova (SN) 2012aw taken at seven epochs during the photospheric phase, from 16 to 120 d after explosion. We corrected for ...interstellar polarization by postulating that the SN polarization is naught near the rest wavelength of the strongest lines – this is later confirmed by our modeling. SN 2012aw exhibits intrinsic polarization, with strong variations across lines, and with a magnitude that grows in the 7000 Å line-free region from 0.1% at 16 d up to 1.2% at 120 d. This behavior is qualitatively similar to observations gathered for other type II SNe. A suitable rotation of Stokes vectors places the bulk of the polarization in
q
, suggesting the ejecta of SN 2012aw is predominantly axisymmetric. Using an upgraded version of our 2D polarized radiative transfer code, we modeled the wavelength- and time-dependent polarization of SN 2012aw. The key observables may be explained by the presence of a confined region of enhanced
56
Ni at ~4000 km s
−1
, which boosts the electron density in a cone having an opening angle of ~50 deg and an observer’s inclination of ~70 deg to the axis of symmetry. With this fixed asymmetry in time, the observed evolution of the SN 2012aw polarization arises from the evolution of the ejecta optical depth, ionization, and the relative importance of multiple versus single scattering. However, the polarization signatures exhibit numerous degeneracies. Cancellation effects at early times imply that low polarization may even occur for ejecta with a large asymmetry. An axisymmetric ejecta with a latitudinal-dependent explosion energy can also yield similar polarization signatures as asymmetry in the
56
Ni distribution. In spite of these uncertainties, SN 2012aw provides additional evidence for the generic asymmetry of type II SN ejecta, of which VLT–FORS spectropolarimetric observations are a decisive and exquisite probe.
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