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Luc Dessart

Publications and source records attributed to Luc Dessart.

At least 109 records · Page 6Linked to original sources
arXiv2018

Type Ib/Ic supernovae: effect of nickel mixing on the early-time color evolution and implications for the progenitors

We investigate the effect of mixing of radioactive nickel ($^{56}$Ni) on the early-time color evolution of Type Ib and Ic supernovae (SNe Ib/Ic) using multi-group radiation hydrodynamics simulations. We consider both helium-rich and helium-poor progenitors. Mixing of $^{56}$Ni is parameterized using a Gaussian distribution function. We find that the early-time color evolution with a weak $^{56}$Ni mixing is characterized by three different phases: initial rapid reddening, blueward evolution due to the delayed effect of $^{56}$Ni heating, and redward evolution thereafter until the transition to the nebular phase. With a strong $^{56}$Ni mixing, the second phase disappears. We compare our models with the early-time color evolution of several SNe Ib/Ic (SN1999ex, SN 2008D, SN 2009jf, iPTF13bvn, SN 1994I, SN 2007gr, SN 2013ge, and 2017ein) and find signatures of relatively weak and strong $^{56}$Ni mixing for SNe Ib and SNe Ic, respectively. This suggests that SNe Ib progenitors are distinct from SN Ic progenitors in terms of helium content and that $^{56}$Ni mixing is generally stronger in the carbon-oxygen core and weaker in the helium-rich envelope. We conclude that the early-time color evolution is a powerful probe of $^{56}$Ni mixing in SNe Ib/Ic.

astro-ph.HE↗
arXiv2018

Impact of clumping on core-collapse supernova radiation

There is both observational and theoretical evidence that the ejecta of core-collapse supernovae (SNe) are structured. Rather than being smooth and homogeneous, the material is made of over-dense and under-dense regions of distinct composition. Here, we explore the effect of clumping on the SN radiation during the photospheric phase using 1-D non-local thermodynamic equilibrium radiative transfer and an ejecta model arising from a blue-supergiant explosion (yielding a Type II-peculiar SN). Neglecting chemical segregation, we adopt a velocity-dependent volume-filling factor approach that assumes that the clumps are small but does not change the column density along any sightline. We find that clumping boosts the recombination rate in the photospheric layers, leading to a faster recession of the photosphere, an increase in bolometric luminosity, and a reddening of the SN colors through enhanced blanketing. The SN bolometric light curve peaks earlier and transitions faster to the nebular phase. On the rise to maximum, the strongest luminosity contrast between our clumped and smooth models is obtained at the epoch when the photosphere has receded to ejecta layers where the clumping factor is only 0.5 -- this clumping factor may be larger in Nature. Clumping is seen to have a similar influence in a Type II-Plateau SN model. As we neglect both porosity and chemical segregation our models underestimate the true impact of clumping. These results warrant further study of the influence of clumping on the observables of other SN types during the photospheric phase.

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arXiv2018

Super-luminous Type II supernovae powered by magnetars

Magnetar power is believed to be at the origin of numerous super-luminous supernovae (SNe) of Type Ic, arising from compact, hydrogen-deficient, Wolf-Rayet type stars. Here, we investigate the properties that magnetar power would have on standard-energy SNe associated with 15-20Msun blue or red supergiant (BSG/RSG) stars. We use a combination of Eulerian grey radiation-hydrodynamics and non-LTE steady-state radiative transfer to study their dynamical, photometric, and spectroscopic properties. Adopting magnetar fields of 1, 3.5, 7 x 10^14G and rotational energies of 0.4, 1, and 3 x 10^51erg, we produce bolometric light curves with a broad maximum covering 50-150d and a magnitude of 10^43-10^44erg/s. The spectra at maximum light are analogous to those of standard SNe II-P but bluer. Although the magnetar energy is channelled roughly in equal proportion between SN kinetic energy and SN luminosity, the latter may be boosted by a factor 10-100 compared to a standard SN II. This influence breaks the observed relation between brightness and expansion rate of standard Type II SNe. Magnetar energy injection also delays recombination and may even cause re-ionization, with a reversal in photospheric temperature and velocity. Depositing the magnetar energy in a narrow mass shell at the ejecta base leads to the formation of a dense shell at a few 1000km/s, which causes a light-curve bump at the end of the photospheric phase. Depositing this energy over a broad range of mass in the inner ejecta, to mimic the effect of multi-dimensional fluid instabilities, prevents the formation of a dense shell and produces an earlier-rising and smoother light curve. The magnetar influence on the SN radiation is generally not visible prior to 20-30d, during which one may discern a BSG from a RSG progenitor. We propose a magnetar model for the super-luminous Type II SN OGLE-SN14-073.

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arXiv2018

A magnetar model for the hydrogen-rich super-luminous supernova iPTF14hls

Transient surveys have recently revealed the existence of H-rich super-luminous supernovae (SLSN; e.g., iPTF14hls, OGLE-SN14-073) characterized by an exceptionally large time-integrated bolometric luminosity, a sustained blue optical color, and Doppler-broadened HI lines at all times. Here, I investigate the effect that a magnetar (initial rotational energy of 4x10^50erg and field strength of 7x10^13G) would have on the properties of a typical Type II SN ejecta (mass of 13.35Msun, kinetic energy of 1.32x10^51erg, 0.077Msun of 56Ni) produced by the terminal explosion of an H-rich blue-supergiant star. I present a non-LTE time-dependent radiative transfer simulation of the resulting photometric and spectroscopic evolution from 1d until 600d after explosion. With magnetar power, the model luminosity and brightness are enhanced, the ejecta is everywhere hotter and more ionised, and the spectrum formation region is much more extended. This magnetar-powered SN ejecta reproduces most of the observed properties of SLSN iPTF14hls, including the sustained brightness of -18mag in the R band, the blue optical color, and the broad HI lines for 600d. The non-extreme magnetar properties, combined with the standard Type II SN ejecta properties offer an interesting alternative to the pair-unstable super-massive star model recently proposed, which involves a highly-energetic and super-massive ejecta. Hence, such Type II SLSNe may differ from standard Type II SNe exclusively through the influence of a magnetar.

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arXiv2018

Supernovae from massive stars with extended tenuous envelopes

Massive stars with a core-halo structure are interesting objects for stellar physics and hydrodynamics. Using simulations for stellar evolution, radiation hydrodynamics, and radiative transfer, we study the explosion of stars with an extended and tenuous envelope (i.e., stars in which 95% of the mass is contained within 10% of the surface radius or less). We consider both H-rich supergiant and He-giant progenitors resulting from close-binary evolution and dying with a final mass of 2.8-5Msun. An extended envelope causes the supernova (SN) shock to brake and a reverse shock to form, sweeping core material into a dense shell. The shock deposited energy, which suffers little degradation from expansion, is trapped in ejecta layers of moderate optical depth, thereby enhancing the SN luminosity at early times. With the delayed 56Ni heating, we find that the resulting optical and near-IR light curves all exhibit a double-peak morphology. We show how an extended progenitor can explain the blue and featureless optical spectra of some Type IIb and Ib SNe. The dense shell formed by the reverse shock leads to line profiles with a smaller and near-constant width. This ejecta property can explain the statistically narrower profiles of Type IIb compared to Type Ib SNe, as well as the peculiar Halpha profile seen in SN1993J. At early times, our He-giant star explosion model shows a high luminosity, a blue color, and featureless spectra reminiscent of the Type Ib SN2008D, suggesting a low-mass progenitor.

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arXiv2017

The detonation of a sub-Chandrasekhar-mass white dwarf at the origin of the low-luminosity Type Ia supernova 1999by

While Chandrasekhar-mass ($M_{\rm Ch}$) models with a low $^{56}\rm{Ni}$ yield can match the peak luminosities of fast-declining, 91bg-like Type Ia supernovae (SNe Ia), they systematically fail to reproduce their faster light-curve evolution. Here we illustrate the impact of a low ejecta mass on the radiative display of low-luminosity SNe Ia, by comparing a sub-$M_{\rm Ch}$ model resulting from the pure central detonation of a C-O White Dwarf (WD) to a $M_{\rm Ch}$ delayed-detonation model with the same $^{56}\rm{Ni}$ yield of 0.12 M$_{\odot}$. Our sub-$M_{\rm Ch}$ model from a 0.90 M$_{\odot}$ WD progenitor has a $\sim$5 day shorter rise time in the integrated UV-optical-IR (uvoir) luminosity, as well as in the $B$-band, and a $\sim$20 per cent higher peak uvoir luminosity ($\sim$1 mag brighter peak $M_B$). This sub-$M_{\rm Ch}$ model also displays bluer maximum-light colours due to the larger specific heating rate, and larger post-maximum uvoir and $B$-band decline rates. The luminosity decline at nebular times is also more pronounced, reflecting the enhanced escape of gamma rays resulting from the lower density of the progenitor WD. The deficit of stable nickel in the innermost ejecta leads to a notable absence of forbidden lines of [Ni II] in the nebular spectra. In contrast, the $M_{\rm Ch}$ model displays a strong line due to [Ni II] 1.939 $μ\rm{m}$, which could in principle serve to distinguish between different progenitor scenarios. Our sub-$M_{\rm Ch}$ model offers an unprecedented agreement with optical and near-infrared observations of the 91bg-like SN 1999by, making a strong case for a WD progenitor significantly below the Chandrasekhar-mass limit for this event and other low-luminosity SNe Ia.

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arXiv2017

Ejecta Mass Diagnostics of Type Ia Supernovae

We present one-dimensional non-local thermodynamic equilibrium time-dependent radiative transfer simulations (using CMFGEN) of two sub-Chandrasekhar (sub-$M_{\rm Ch}$), one $M_{\rm Ch}$ and one super-$M_{\rm Ch}$ Type Ia SN ejecta models. Three originate from $M_{\rm Ch}$ delayed detonation models, and the fourth is a sub-$M_{\rm Ch}$ detonation model. Ejecta masses are 1.02, 1.04, 1.40, and 1.70 M$_\odot$, and all models have 0.62 M$_\odot$ of $^{56}{\rm Ni}$. Sub-$M_{\rm Ch}$ model light curves evolve faster, reaching bolometric maximum 2--3 days earlier and having 3--4 days shorter bolometric half light widths. The models vary by $\sim$12 per cent at maximum bolometric luminosity and by 0.17 mag in $B_{\rm max}$. While $ΔM_{15}(B)$ increases with ejecta mass it only varies by $\sim$5 per cent around 1 mag. Sub-$M_{\rm Ch}$ models are 0.25 mag bluer in $B-R$ at $B_{\rm max}$. Optical spectra share many similarities, but lower mass models exhibit less UV line blanketing during the photospheric phase. At nebular times, significant NIR spectroscopic differences are seen. In particular, emission lines of the Ca II NIR triplet; [S III] $λλ$9068,9530; [Ca II] $λλ$7291,7324; [Ar III] $λλ$7135,7751; and [Ni II] 1.939 $μ$m are stronger in higher mass models. The [Ni II] 1.939 $μ$m line is absent in the sub-$M_{\rm Ch}$ detonation model, and provides a valuable potential tool to distinguish sub-$M_{\rm Ch}$ explosions from $M_{\rm Ch}$ explosions. In general, the nebular phase models are too highly ionized. We attribute this to the neglect of clumping and/or the distribution of intermediate mass and iron group elements. The two sub-$M_{\rm Ch}$ models, while exploded by different mechanisms, can be distinguished in the $J$ and $H$ bands at late times (e.g., $+200$ days).

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arXiv2017

Progenitors of low-luminosity Type II-Plateau supernovae

The progenitors of low-luminosity Type II-Plateau supernovae (SNe II-P) are believed to be red supergiant (RSG) stars, but there is much disparity in the literature concerning their mass at core collapse and therefore on the main sequence. Here, we model the SN radiation arising from the low-energy explosion of RSG stars of 12, 25, and 27 M$_{\odot}$ on the main sequence and formed through single star evolution. Despite the narrow range in ejecta kinetic energy (2.5$-$4.2$\times$10$^{50}$ erg) in our model set, the SN observables from our three models are significantly distinct, reflecting the differences in progenitor structure (e.g., surface radius, H-rich envelope mass, He-core mass). Our higher mass RSG stars give rise to Type II SNe that tend to have bluer colors at early times, a shorter photospheric phase, and a faster declining $V$-band light curve (LC) more typical of Type II-linear SNe, in conflict with the LC plateau observed for low-luminosity SNe II. The complete fallback of the CO core in the low-energy explosions of our high mass RSG stars prevents the ejection of any ${}^{56}$Ni (nor any core O or Si), in contrast to low-luminosity SNe II-P, which eject at least 0.001 M$_{\odot}$ of ${}^{56}$Ni. In contrast to observations, type II SN models from higher mass RSGs tend to show an H$α$ absorption that remains broad at late times (due to a larger velocity at the base of the H-rich envelope). In agreement with the analyses of pre-explosion photometry, we conclude that low-luminosity SNe II-P likely arise from low-mass rather than high-mass RSG stars.

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arXiv2017

Type II supernova spectral diversity II: Spectroscopic and photometric correlations

We present an analysis of observed trends and correlations between a large range of spectral and photometric parameters of more than 100 type II supernovae (SNe~II), during the photospheric phase. We define a common epoch for all SNe of 50 days post-explosion where the majority of the sample is likely to be under similar physical conditions. Several correlation matrices are produced to search for interesting trends between more than 30 distinct light-curve and spectral properties that characterize the diversity of SNe~II. Overall, SNe with higher expansion velocities are brighter, have more rapidly declining light-curves, shorter plateau durations, and higher $^{56}$Ni masses. Using a larger sample than previous studies, we argue that `$Pd$' - the plateau duration from the transition of the initial to `plateau' decline rates to the end of the `plateau' - is a better indicator of the hydrogen envelope mass than the traditionally used optically thick phase duration ($OPTd$: explosion epoch to end of plateau). This argument is supported by the fact that $Pd$ also correlates with s$_3$, the light-curve decline rate at late times: lower $Pd$ values correlate with larger s$_3$ decline rates. Large s$_3$ decline rates are likely related to lower envelope masses that enables gamma-ray escape. We also find a significant anticorrelation between $Pd$ and s$_2$ (the plateau decline rate), confirming the long standing hypothesis that faster declining SNe~II (SNe~IIL) are the result of explosions with lower hydrogen envelope masses and therefore have shorter $Pd$ values.

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arXiv2017

Type II supernova spectral diversity I: Observations, sample characterization and spectral line evolution

We present 888 visual-wavelength spectra of 122 nearby type II supernovae (SNe II) obtained between 1986 and 2009, and ranging between 3 and 363 days post explosion. In this first paper, we outline our observations and data reduction techniques, together with a characterization based on the spectral diversity of SNe~II. A statistical analysis of the spectral matching technique is discussed as an alternative to non-detection constraints for estimating SN explosion epochs. The time evolution of spectral lines is presented and analysed in terms of how this differs for SNe of different photometric, spectral, and environmental properties: velocities, pseudo-equivalent widths, decline rates, magnitudes, time durations, and environment metallicity. Our sample displays a large range in ejecta expansion velocities, from $\sim9600$ to $\sim1500$ km s$^{-1}$ at 50 days post explosion with a median H$_α$ value of 7300 km s$^{-1}$. This is most likely explained through differing explosion energies. Significant diversity is also observed in the absolute strength of spectral lines, characterised through their pseudo-equivalent widths. This implies significant diversity in both temperature evolution (linked to progenitor radius) and progenitor metallicity between different SNe~II. Around 60\% of our sample show an extra absorption component on the blue side of the H$_α$ P-Cygni profile ("Cachito" feature) between 7 and 120 days since explosion. Studying the nature of Cachito, we conclude that these features at early times (before $\sim35$ days) are associated with \ion{Si}{2} $\lambda6355$, while past the middle of the plateau phase they are related to high velocity (HV) features of hydrogen lines.

astro-ph.HE↗
arXiv2017

Evidence for sub-Chandrasekhar-mass progenitors of Type Ia supernovae at the faint end of the width-luminosity relation

The faster light-curve evolution of low-luminosity Type Ia supernovae (SNe Ia) suggests that they could result from the explosion of white dwarf (WD) progenitors below the Chandrasekhar mass ($M_{\rm Ch}$). Here we present 1D non-LTE time-dependent radiative transfer simulations of pure central detonations of carbon-oxygen WDs with a mass ($M_\rm{tot}$) between 0.88 M$_{\odot}$ and 1.15 M$_{\odot}$, and a $^{56}\rm{Ni}$ yield between 0.08 M$_{\odot}$ and 0.84 M$_{\odot}$. Their lower ejecta density compared to $M_{\rm Ch}$ models results in a more rapid increase of the luminosity at early times and an enhanced $γ$-ray escape fraction past maximum light. Consequently, their bolometric light curves display shorter rise times and larger post-maximum decline rates. Moreover, the higher $M(^{56}\rm{Ni})/M_\rm{tot}$ ratio at a given $^{56}\rm{Ni}$ mass enhances the temperature and ionization level in the spectrum-formation region for the less luminous models, giving rise to bluer colours at maximum light and a faster post-maximum evolution of the $B-V$ colour. For sub-$M_{\rm Ch}$ models fainter than $M_B\approx -18.5$ mag at peak, the greater bolometric decline and faster colour evolution lead to a larger $B$-band post-maximum decline rate, $ΔM_{15}(B)$. In particular, all of our previously-published $M_{\rm Ch}$ models (standard and pulsational delayed detonations) are confined to $ΔM_{15}(B) < 1.4$ mag, while the sub-$M_{\rm Ch}$ models with $M_\rm{tot}\lesssim 1$ M$_{\odot}$ extend beyond this limit to $ΔM_{15}(B)\approx 1.65$ mag for a peak $M_B\approx -17$ mag, in better agreement with the observed width-luminosity relation (WLR). Regardless of the precise ignition mechanism, these simulations suggest that fast-declining SNe Ia at the faint end of the WLR could result from the explosion of WDs whose mass is significantly below the Chandrasekhar limit.

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arXiv2017

Explosion of red-supergiant stars: influence of the atmospheric structure on shock breakout and the early-time supernova radiation

Early-time observations of the Type II supernovae (SNe) 2013cu and 2013fs have revealed an interaction of ejecta with material near the star surface. Unlike the Type IIn SN2010jl, which interacts with a dense wind for ~1yr, the interaction ebbs after 2-3d, suggesting a dense and compact circumstellar envelope. Here, we use multi-group radiation-hydrodynamics and non-local-thermodynamic-equilibrium radiative transfer to explore the properties of red supergiant (RSG) star explosions embedded in a variety of dense envelopes. We consider the cases of an extended static atmosphere or a steady-state wind, adopting a range of mass loss rates. The shock-breakout signal, the SN radiation up to 10d, and the ejecta dynamics are strongly influenced by the properties of this nearby environment. This compromises the use of early-time observations to constrain Rstar. The presence of narrow lines for 2-3d in 2013fs and 2013cu require a cocoon of material of ~0.01Msun out to 5-10Rstar. Spectral lines evolve from electron-scattering to Doppler broadened, with a growing blueshift of their emission peaks. Recent studies propose a super-wind phase with a mass loss rate from 0.001 up to 1Msun/yr in the last months/years of the RSG life, although there is no observational constraint that this external material is a steady-state outflow. Alternatively, observations may be explained by the explosion of a RSG star inside its complex atmosphere. Indeed, spatially resolved observations reveal that RSG stars have extended atmospheres, with the presence of downflows and upflows out to several Rstar, even in a standard RSG like Betelgeuse. Mass loading in the region intermediate between star and wind can accommodate the 0.01Msun needed to explain the observations of 2013fs. A puzzling super-wind phase prior to core-collapse may be therefore superfluous [Abridged].

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arXiv2017

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.

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arXiv2017

Type Ib and IIb supernova progenitors in interacting binary systems

We explore properties of Type Ib and IIb SN progenitors that are produced by stable mass transfer in binary systems, using a new grid of stellar evolution models from an initial primary mass in the range of 10 - 18 $\mathrm{M_\odot}$ at solar and Large Magellanic Cloud metallicities. We find that blue and yellow supergiant SN IIb progenitors (e.g., of SN 2008ax, SN 2011dh, SN 2016gkg) have a hydrogen envelope mass less than about 0.15 $\mathrm{M_\odot}$, mostly resulting from early Case B mass transfer with relatively low initial masses and/or low metallicity. Red supergiant (RSG) SN IIb progenitors (e.g., of SN 1993J, SN 2013df) are produced via late Case B mass transfer and have a more massive hydrogen envelope ($M_\mathrm{H,env} > 0.15~\mathrm{M_\odot}$). SN Ib progenitors are predominantly produced by early Case B mass transfer. Our models predict that SN IIb progenitors are systematically more luminous in the optical ($-8.0 \lesssim M_\mathrm{V} \lesssim -5.0$) than the majority of SN Ib progenitors ($M_\mathrm{V} \gtrsim -5.0$) for our considered initial mass range. However, the optically bright progenitor of SN Ib iPTF13bvn (i.e., $M_\mathrm{V} \simeq -6.5$) can be well explained by a relatively low-mass progenitor with a final mass of $\sim 3.0~\mathrm{M_\odot}$. The event rate of blue and yellow SN IIb progenitors would increase as metallicity decreases, while the event rate of SN Ib progenitors would decrease instead. By contrast, the population of RSG SN IIb progenitors would not be significantly affected by metallicity.

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arXiv2017

Modules for Experiments in Stellar Astrophysics (MESA): Binaries, Pulsations, and Explosions

We substantially update the capabilities of the open-source software instrument Modules for Experiments in Stellar Astrophysics (MESA). MESA can now simultaneously evolve an interacting pair of differentially rotating stars undergoing transfer and loss of mass and angular momentum, greatly enhancing the prior ability to model binary evolution. New MESA capabilities in fully coupled calculation of nuclear networks with hundreds of isotopes now allow MESA to accurately simulate advanced burning stages needed to construct supernova progenitor models. Implicit hydrodynamics with shocks can now be treated with MESA, enabling modeling of the entire massive star lifecycle, from pre-main sequence evolution to the onset of core collapse and nucleosynthesis from the resulting explosion. Coupling of the GYRE non-adiabatic pulsation instrument with MESA allows for new explorations of the instability strips for massive stars while also accelerating the astrophysical use of asteroseismology data. We improve treatment of mass accretion, giving more accurate and robust near-surface profiles. A new MESA capability to calculate weak reaction rates "on-the-fly" from input nuclear data allows better simulation of accretion induced collapse of massive white dwarfs and the fate of some massive stars. We discuss the ongoing challenge of chemical diffusion in the strongly coupled plasma regime, and exhibit improvements in MESA that now allow for the simulation of radiative levitation of heavy elements in hot stars. We close by noting that the MESA software infrastructure provides bit-for-bit consistency for all results across all the supported platforms, a profound enabling capability for accelerating MESA's development.

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arXiv2016

A study of the low-luminosity Type II-Plateau supernova 2008bk

Supernova (SN) 2008bk is a well observed low-luminosity Type II event visually associated with a low-mass red-supergiant progenitor. To model SN 2008bk, we evolve a 12Msun star from the main sequence until core collapse, when it has a total mass of 9.88Msun, a He-core mass of 3.22Msun, and a radius of 502Rsun. We then artificially trigger an explosion that produces 8.29Msun of ejecta with a total energy of 2.5x10^50erg and ~0.009Msun of 56Ni. We model the subsequent evolution of the ejecta with non-Local-Thermodynamic-Equilibrium time-dependent radiative transfer. Although somewhat too luminous and energetic, this model reproduces satisfactorily the multi-band light curves and multi-epoch spectra of SN 2008bk, confirming the suitability of a low-mass massive star progenitor. As in other low-luminosity SNe II, the structured Halpha profile at the end of the plateau phase is probably caused by BaII 6496.9A rather than asphericity. We discuss the sensitivity of our results to changes in progenitor radius and mass, as well as chemical mixing. A 15% increase in progenitor radius causes a 15% increase in luminosity and a 0.2mag V-band brightening of the plateau but leaves its length unaffected. An increase in ejecta mass by 10% lengthens the plateau by ~10d. Chemical mixing introduces slight changes to the bolometric light curve, limited to the end of the plateau, but has a large impact on colours and spectra at nebular times.

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arXiv2016

On Variations Of Pre-Supernova Model Properties

We explore the variation in single star 15-30 $\rm{M}_{\odot}$, non-rotating, solar metallicity, pre-supernova MESA models due to changes in the number of isotopes in a fully-coupled nuclear reaction network and adjustments in the mass resolution. Within this two-dimensional plane we quantitatively detail the range of core masses at various stages of evolution, mass locations of the main nuclear burning shells, electron fraction profiles, mass fraction profiles, burning lifetimes, stellar lifetimes, and compactness parameter at core-collapse for models with and without mass loss. Up to carbon burning we generally find mass resolution has a larger impact on the variations than the number of isotopes, while the number of isotopes plays a more significant role in determining the span of the variations for neon, oxygen and silicon burning. Choice of mass resolution dominates the variations in the structure of the intermediate convection zone and secondary convection zone during core and shell hydrogen burning respectively, where we find a minimum mass resolution of $\approx$ 0.01 $\rm{M}_{\odot}$ is necessary to achieve convergence in the helium core mass at the $\approx$5% level. On the other hand, at the onset of core-collapse we find $\approx$30% variations in the central electron fraction and mass locations of the main nuclear burning shells, a minimum of $\approx$127 isotopes is needed to attain convergence of these values at the $\approx$10% level.

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arXiv2016

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 $M_{\rm e}$ of 1.7$-$5.2M$_\odot$, kinetic energies $E_{\rm kin}$ of 0.6$-$5.0$\times$10$^{51}$erg, and $^{56}$Ni masses of 0.05$-$0.30M$_\odot$. We find a strong correlation between the $^{56}$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 ($V-R$) at 10d past $R$-band maximum. The quantity $V_{\rm m} \equiv \sqrt{2E_{\rm kin}/M_{\rm e}}$ is comparable to the Doppler velocity measured from HeI 5875Å at maximum in SNe IIb/Ib, although some scatter arises from the uncertain level of chemical mixing. The OI7772Å 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 $\sim$1.05$μ$m 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.

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