| 1. |
- Bulla, M., et al.
(författare)
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Polarization spectral synthesis for Type Ia supernova explosion models
- 2015
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 450:1, s. 967-981
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Tidskriftsartikel (refereegranskat)abstract
- We present a Monte Carlo radiative transfer technique for calculating synthetic spectropolarimetry for multidimensional supernova explosion models. The approach utilizes 'virtual-packets' that are generated during the propagation of the Monte Carlo quanta and used to compute synthetic observables for specific observer orientations. Compared to extracting synthetic observables by direct binning of emergent Monte Carlo quanta, this virtual-packet approach leads to a substantial reduction in the Monte Carlo noise. This is not only vital for calculating synthetic spectropolarimetry (since the degree of polarization is typically very small) but also useful for calculations of light curves and spectra. We first validate our approach via application of an idealized test code to simple geometries. We then describe its implementation in the Monte Carlo radiative transfer code ARTIS and present test calculations for simple models for Type Ia supernovae. Specifically, we use the well-known one-dimensional W7 model to verify that our scheme can accurately recover zero polarization from a spherical model, and to demonstrate the reduction in Monte Carlo noise compared to a simple packet-binning approach. To investigate the impact of aspherical ejecta on the polarization spectra, we then use ARTIS to calculate synthetic observables for prolate and oblate ellipsoidal models with Type Ia supernova compositions.
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| 2. |
- Bulla, M., et al.
(författare)
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Predicting polarization signatures for double-detonation and delayed-detonation models of Type Ia supernovae
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 462:1, s. 1039-1056
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Tidskriftsartikel (refereegranskat)abstract
- Calculations of synthetic spectropolarimetry are one means to test multidimensional explosion models for Type Ia supernovae. In a recent paper, we demonstrated that the violent merger of a 1.1 and 0.9 M-circle dot white dwarf binary system is too asymmetric to explain the low polarization levels commonly observed in normal Type Ia supernovae. Here, we present polarization simulations for two alternative scenarios: the sub-Chandrasekhar mass double-detonation and the Chandrasekhar mass delayed-detonation model. Specifically, we study a 2D double-detonation model and a 3D delayed-detonation model, and calculate polarization spectra for multiple observer orientations in both cases. We find modest polarization levels (<1 per cent) for both explosion models. Polarization in the continuum peaks at similar to 0.1-0.3 per cent and decreases aftermaximum light, in excellent agreement with spectropolarimetric data of normal Type Ia supernovae. Higher degrees of polarization are found across individual spectral lines. In particular, the synthetic Si II lambda 6355 profiles are polarized at levels that match remarkably well the values observed in normal Type Ia supernovae, while the low degrees of polarization predicted across the O I lambda 7774 region are consistent with the non-detection of this feature in current data. We conclude that our models can reproduce many of the characteristics of both flux and polarization spectra for well-studied Type Ia supernovae, such as SN 2001el and SN 2012fr. However, the two models considered here cannot account for the unusually high level of polarization observed in extreme cases such as SN 2004dt.
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| 3. |
- Bulla, M., et al.
(författare)
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Type Ia supernovae from violent mergers of carbon-oxygen white dwarfs : polarization signatures
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 455:1, s. 1060-1070
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Tidskriftsartikel (refereegranskat)abstract
- The violent merger of two carbon-oxygen white dwarfs has been proposed as a viable progenitor for some Type Ia supernovae. However, it has been argued that the strong ejecta asymmetries produced by this model might be inconsistent with the low degree of polarization typically observed in Type Ia supernova explosions. Here, we test this claim by carrying out a spectropolarimetric analysis for the model proposed by Pakmor et al. for an explosion triggered during the merger of a 1.1 and 0.9 M-circle dot carbon-oxygen white dwarf binary system. Owing to the asymmetries of the ejecta, the polarization signal varies significantly with viewing angle. We find that polarization levels for observers in the equatorial plane are modest (less than or similar to 1 per cent) and show clear evidence for a dominant axis, as a consequence of the ejecta symmetry about the orbital plane. In contrast, orientations out of the plane are associated with higher degrees of polarization and departures from a dominant axis. While the particular model studied here gives a good match to highly polarized events such as SN 2004dt, it has difficulties in reproducing the low polarization levels commonly observed in normal Type Ia supernovae. Specifically, we find that significant asymmetries in the element distribution result in a wealth of strong polarization features that are not observed in the majority of currently available spectropolarimetric data of Type Ia supernovae. Future studies will map out the parameter space of the merger scenario to investigate if alternative models can provide better agreement with observations.
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| 4. |
- Diehl, Roland, et al.
(författare)
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Early Ni-56 decay gamma rays from SN2014J suggest an unusual explosion
- 2014
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 345:6201, s. 1162-1165
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Tidskriftsartikel (refereegranskat)abstract
- Type Ia supernovae result from binary systems that include a carbon-oxygen white dwarf, and these thermonuclear explosions typically produce 0.5 solar mass of radioactive Ni-56. The Ni-56 is commonly believed to be buried deeply in the expanding supernova cloud. In SN2014J, we detected the lines at 158 and 812 kiloelectron volts from Ni-56 decay (time similar to 8.8 days) earlier than the expected several-week time scale, only similar to 20 days after the explosion and with flux levels corresponding to roughly 10% of the total expected amount of Ni-56. Some mechanism must break the spherical symmetry of the supernova and at the same time create a major amount of Ni-56 at the outskirts. A plausible explanation is that a belt of helium from the companion star is accreted by the white dwarf, where this material explodes and then triggers the supernova event.
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| 5. |
- Fink, Michael, et al.
(författare)
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Three-dimensional pure deflagration models with nucleosynthesis and synthetic observables for Type Ia supernovae
- 2014
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 438:2, s. 1762-1783
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Tidskriftsartikel (refereegranskat)abstract
- We investigate whether pure deflagration models of Chandrasekhar-mass carbon-oxygen white dwarf stars can account for one or more subclass of the observed population of Type Ia supernova (SN Ia) explosions. We compute a set of 3D full-star hydrodynamic explosion models, in which the deflagration strength is parametrized using the multispot ignition approach. For each model, we calculate detailed nucleosynthesis yields in a post-processing step with a 384 nuclide nuclear network. We also compute synthetic observables with our 3D Monte Carlo radiative transfer code for comparison with observations. For weak and intermediate deflagration strengths (energy release E-nuc less than or similar to 1.1 x 10(51) erg), we find that the explosion leaves behind a bound remnant enriched with 3 to 10 per cent (by mass) of deflagration ashes. However, we do not obtain the large kick velocities recently reported in the literature. We find that weak deflagrations with E-nuc similar to 0.5 x 10(51) erg fit well both the light curves and spectra of 2002cx-like SNe Ia, and models with even lower explosion energies could explain some of the fainter members of this subclass. By comparing our synthetic observables with the properties of SNe Ia, we can exclude the brightest, most vigorously ignited models as candidates for any observed class of SN Ia: their B - V colours deviate significantly from both normal and 2002cx-like SNe Ia and they are too bright to be candidates for other subclasses.
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| 6. |
- Foley, Ryan J., et al.
(författare)
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Extensive HST ultraviolet spectra and multiwavelength observations of SN 2014J in M82 indicate reddening and circumstellar scattering by typical dust
- 2014
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 443:4, s. 2887-2906
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Tidskriftsartikel (refereegranskat)abstract
- SN 2014J in M82 is the closest detected Type Ia supernova (SN Ia) in at least 28 yr and perhaps in 410 yr. Despite its small distance of 3.3 Mpc, SN 2014J is surprisingly faint, peaking at V = 10.6 mag, and assuming a typical SN Ia luminosity, we infer an observed visual extinction of A(V) = 2.0 +/- 0.1 mag. But this picture, with R-V = 1.6 +/- 0.2, is too simple to account for all observations. We combine 10 epochs (spanning a month) of HST/Space Telescope Imaging Spectrograph (STIS) ultraviolet through near-infrared spectroscopy with HST/Wide Field Camera 3 (WFC3), Katzman Automatic Imaging Telescope, and FanCam photometry from the optical to the infrared and nine epochs of high-resolution TRES (Tillinghast Reflection Echelle Spectrograph) spectroscopy to investigate the sources of extinction and reddening for SN 2014J. We argue that the wide range of observed properties for SN 2014J is caused by a combination of dust reddening, likely originating in the interstellar medium of M82, and scattering off circumstellar material. For this model, roughly half of the extinction is caused by reddening from typical dust (E(B - V) = 0.45 mag and R-V = 2.6) and roughly half by scattering off Large Magellanic Cloud-like dust in the circumstellar environment of SN 2014J.
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| 7. |
- Foley, Ryan J., et al.
(författare)
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THE FIRST MAXIMUM-LIGHT ULTRAVIOLET THROUGH NEAR-INFRARED SPECTRUM OF A TYPE Ia SUPERNOVA
- 2012
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Ingår i: THE ASTROPHYSICAL JOURNAL LETTERS. - 2041-8205. ; 753:1, s. L5-
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Tidskriftsartikel (refereegranskat)abstract
- We present the first maximum-light ultraviolet (UV) through near-infrared (NIR) Type Ia supernova (SN Ia) spectrum. This spectrum of SN 2011iv was obtained nearly simultaneously by the Hubble Space Telescope at UV/optical wavelengths and the Magellan Baade telescope at NIR wavelengths. These data provide the opportunity to examine the entire maximum-light SN Ia spectral energy distribution. Since the UV region of an SN Ia spectrum is extremely sensitive to the composition of the outer layers of the explosion, which are transparent at longer wavelengths, this unprecedented spectrum can provide strong constraints on the composition of the SN ejecta, and similarly the SN explosion and progenitor system. SN 2011iv is spectroscopically normal, but has a relatively fast decline (Delta m(15)(B) = 1.69 +/- 0.05 mag). We compare SN 2011iv to other SNe Ia with UV spectra near maximum light and examine trends between UV spectral properties, light-curve shape, and ejecta velocity. We tentatively find that SNe with similar light-curve shapes but different ejecta velocities have similar UV spectra, while those with similar ejecta velocities but different light-curve shapes have very different UV spectra. Through a comparison with explosion models, we find that both a solar-metallicity W7 and a zero-metallicity delayed-detonation model provide a reasonable fit to the spectrum of SN 2011iv from the UV to the NIR.
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| 8. |
- Gall, E. E. E., et al.
(författare)
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An updated Type II supernova Hubble diagram
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 611
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Tidskriftsartikel (refereegranskat)abstract
- We present photometry and spectroscopy of nine Type II-P/L supernovae (SNe) with redshifts in the 0.045 less than or similar to z less than or similar to 0.335 range, with a view to re-examining their utility as distance indicators. Specifically, we apply the expanding photosphere method (EPM) and the standardized candle method (SCM) to each target, and find that both methods yield distances that are in reasonable agreement with each other. The current record-holder for the highest-redshift spectroscopically confirmed supernova (SN) II-P is PS1-13bni (z = 0.335(-0 .012)(+ 0.009)), and illustrates the promise of Type II SNe as cosmological tools. We updated existing EPM and SCM Hubble diagrams by adding our sample to those previously published. Within the context of Type II SN distance measuring techniques, we investigated two related questions. First, we explored the possibility of utilising spectral lines other than the traditionally used Fe II lambda 5169 to infer the photospheric velocity of SN ejecta. Using local well-observed objects, we derive an epoch-dependent relation between the strong Balmer line and Fe II lambda 5169 velocities that is applicable 30 to 40 days post-explosion. Motivated in part by the continuum of key observables such as rise time and decline rates exhibited from II-P to II-L SNe, we assessed the possibility of using Hubble-flow Type II-L SNe as distance indicators. These yield similar distances as the Type II-P SNe. Although these initial results are encouraging, a significantly larger sample of SNe II-L would be required to draw definitive conclusions.
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| 9. |
- Gall, E. E. E., et al.
(författare)
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Applying the expanding photosphere and standardized candle methods to Type II-Plateau supernovae at cosmologically significant redshifts
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 592
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Tidskriftsartikel (refereegranskat)abstract
- Based on optical imaging and spectroscopy of the Type II-Plateau SN 2013eq, we present a comparative study of commonly used distance determination methods based on Type II supernovae. The occurrence of SN 2013eq in the Hubble flow (z = 0.041 +/- 0.001) prompted us to investigate the implications of the difference between angular and luminosity distances within the framework of the expanding photosphere method (EPM) that relies upon a relation between flux and angular size to yield a distance. Following a re-derivation of the basic equations of the EPM for SNe at non-negligible redshifts, we conclude that the EPM results in an angular distance. The observed flux should be converted into the SN rest frame and the angular size, theta, has to be corrected by a factor of (1 + z)(2). Alternatively, the EPM angular distance can be converted to a luminosity distance by implementing a modification of the angular size. For SN 2013eq, we find EPM luminosity distances of D-L = 151 +/- 18 Mpc and D-L = 164 +/- 20 Mpc by making use of different sets of dilution factors taken from the literature. Application of the standardized candle method for Type II-P SNe results in an independent luminosity distance estimate (D-L = 168 +/- 16 Mpc) that is consistent with the EPM estimate.
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| 10. |
- Goobar, Ariel, et al.
(författare)
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CONSTRAINTS ON THE ORIGIN OF THE FIRST LIGHT FROM SN 2014J
- 2015
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 799:1, s. 106-
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Tidskriftsartikel (refereegranskat)abstract
- We study the very early light curve of supernova 2014J (SN 2014J) using the high-cadence broad-band imaging data obtained by the Kilodegree Extremely Little Telescope, which fortuitously observed M 82 around the time of the explosion, starting more than 2 months prior to detection, with up to 20 observations per night. These observations are complemented by observations in two narrow-band filters used in an Ha survey of nearby galaxies by the intermediate Palomar Transient Factory that also captured the first days of the brightening of the supernova. The evolution of the light curves is consistent with the expected signal from the cooling of shock heated material of large scale dimensions, greater than or similar to 1R(circle dot). This could be due to heated material of the progenitor, a companion star or pre-existing circumstellar environment, e.g., in the form of an accretion disk. Structure seen in the light curves during the first days after explosion could also originate from radioactive material in the outer parts of an exploding white dwarf, as suggested from the early detection of gamma-rays. The model degeneracy translates into a systematic uncertainty of +/- 0.3 days on the estimate of the first light from SN 2014J.
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| 11. |
- Inserra, C., et al.
(författare)
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OGLE-2013-SN-079 : A LONELY SUPERNOVA CONSISTENT WITH A HELIUM SHELL DETONATION
- 2015
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Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 799:1
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Tidskriftsartikel (refereegranskat)abstract
- We present observational data for a peculiar supernova discovered by the OGLE-IV survey and followed by the Public ESO Spectroscopic Survey for Transient Objects. The inferred redshift of z = 0.07 implies an absolute magnitude in the rest-frame I-band of M-1 similar to -17.6 mag. This places it in the luminosity range between normal Type Ia SNe and novae. Optical and near infrared spectroscopy reveal mostly Ti and Ca lines, and an unusually red color arising from strong depression of flux at rest wavelengths <5000 angstrom. To date, this is the only reported SN showing Ti-dominated spectra. The data are broadly consistent with existing models for the pure detonation of a helium shell around a low-mass CO white dwarf and double-detonation models that include a secondary detonation of a CO core following a primary detonation in an overlying helium shell.
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| 12. |
- Johansson, Joel, et al.
(författare)
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Spitzer observations of SN 2014J and properties of mid-IR emission in Type Ia supernovae
- 2017
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 466:3, s. 3442-3449
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Tidskriftsartikel (refereegranskat)abstract
- SN 2014J in M 82 is the closest Type Ia supernova (SN Ia) in decades. The proximity allows for detailed studies of supernova physics and provides insights into the circumstellar and interstellar environment. In this work, we analyse Spitzer mid-infrared (mid-IR) data of SN 2014J in the 3.6 and 4.5 mu m wavelength range, together with several other nearby and well-studied SNe Ia. We compile the first composite mid-IR light-curve templates from our sample of SNe Ia, spanning the range from before peak brightness well into the nebular phase. Our observations indicate that SNe Ia form a very homogeneous class of objects at these wavelengths. Using the low-reddening supernovae for comparison, we constrain possible thermal emission from circumstellar dust around the highly reddened SN 2014J. We also study SNe 2006X and 2007le, where the presence of matter in the circumstellar environment has been suggested. No significant mid-IR excess is detected, allowing us to place upper limits on the amount of pre-existing dust in the circumstellar environment. For SN 2014J, M-dust less than or similar to 10(-5) M-circle dot within r(dust) similar to 10(17) cm, which is insufficient to account for the observed extinction. Similar limits are obtained for SNe 2006X and 2007le.
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| 13. |
- Kosenko, D., et al.
(författare)
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Oxygen emission in remnants of thermonuclear supernovae as a probe for their progenitor system
- 2015
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 449:2, s. 1441-1448
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Tidskriftsartikel (refereegranskat)abstract
- Recent progress in numerical simulations of thermonuclear supernova explosions brings up a unique opportunity in studying the progenitors of Type Ia supernovae. Coupling state-of-the-art explosion models with detailed hydrodynamical simulations of the supernova remnant evolution and the most up-to-date atomic data for X-ray emission calculations makes it possible to create realistic synthetic X-ray spectra for the supernova remnant phase. Comparing such spectra with high-quality observations of supernova remnants could allow us to constrain the explosion mechanism and the progenitor of the supernova. The present study focuses in particular on the oxygen emission line properties in young supernova remnants, since different explosion scenarios predict a different amount and distribution of this element. Analysis of the soft X-ray spectra from supernova remnants in the Large Magellanic Cloud and confrontation with remnant models for different explosion scenarios suggest that SNR 0509-67.5 could originate from a delayed detonation explosion and SNR 0519-69.0 from an oxygen-rich merger.
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| 14. |
- Kromer, Markus, et al.
(författare)
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Deflagrations in hybrid CONe white dwarfs : a route to explain the faint Type Iax supernova 2008ha
- 2015
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 450:3, s. 3045-3053
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Tidskriftsartikel (refereegranskat)abstract
- Stellar evolution models predict the existence of hybrid white dwarfs (WDs) with a carbon-oxygen core surrounded by an oxygen-neon mantle. Being born with masses similar to 1.1 M-aS (TM), hybrid WDs in a binary system may easily approach the Chandrasekhar mass (M-Ch) by accretion and give rise to a thermonuclear explosion. Here, we investigate an off-centre deflagration in a near-M-Ch hybrid WD under the assumption that nuclear burning only occurs in carbon-rich material. Performing hydrodynamics simulations of the explosion and detailed nucleosynthesis post-processing calculations, we find that only 0.014 M-aS (TM) of material is ejected while the remainder of the mass stays bound. The ejecta consist predominantly of iron-group elements, O, C, Si and S. We also calculate synthetic observables for our model and find reasonable agreement with the faint Type Iax SN 2008ha. This shows for the first time that deflagrations in near-M-Ch WDs can in principle explain the observed diversity of Type Iax supernovae. Leaving behind a near-M-Ch bound remnant opens the possibility for recurrent explosions or a subsequent accretion-induced collapse in faint Type Iax SNe, if further accretion episodes occur. From binary population synthesis calculations, we find the rate of hybrid WDs approaching M-Ch to be of the order of 1 per cent of the Galactic SN Ia rate.
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| 15. |
- Kromer, Markus, et al.
(författare)
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SN 2010LP-A TYPE IA SUPERNOVA FROM A VIOLENT MERGER OF TWO CARBON-OXYGEN WHITE DWARFS
- 2013
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Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 778:1
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Tidskriftsartikel (refereegranskat)abstract
- SN 2010lp is a subluminous Type Ia supernova (SN Ia) with slowly evolving lightcurves. Moreover, it is the only subluminous SN Ia observed so far that shows narrow emission lines of [O I] in late-time spectra, indicating unburned oxygen close to the center of the ejecta. Most explosion models for SNe Ia cannot explain the narrow [O I] emission. Here, we present hydrodynamic explosion and radiative transfer calculations showing that the violent merger of two carbon-oxygen white dwarfs of 0.9 and 0.76 M-circle dot adequately reproduces the early-time observables of SN 2010lp. Moreover, our model predicts oxygen close to the center of the explosion ejecta, a pre-requisite for narrow [O I] emission in nebular spectra as observed in SN 2010lp.
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| 16. |
- Kromer, Markus, et al.
(författare)
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The peculiar Type Ia supernova iPTF14atg : Chandrasekhar-mass explosion or violent merger?
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 459:4, s. 4428-4439
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Tidskriftsartikel (refereegranskat)abstract
- iPTF14atg, a subluminous peculiar Type Ia supernova (SN Ia) similar to SN 2002es, is the first SN Ia for which a strong UV flash was observed in the early-time light curves. This has been interpreted as evidence for a single-degenerate (SD) progenitor system, where such a signal is expected from interactions between the SN ejecta and the non-degenerate companion star. Here, we compare synthetic observables of multidimensional state-of-the-art explosion models for different progenitor scenarios to the light curves and spectra of iPTF14atg. From our models, we have difficulties explaining the spectral evolution of iPTF14atg within the SD progenitor channel. In contrast, we find that a violent merger of two carbon-oxygen white dwarfs with 0.9 and 0.76 M-aS (TM), respectively, provides an excellent match to the spectral evolution of iPTF14atg from 10 d before to several weeks after maximum light. Our merger model does not naturally explain the initial UV flash of iPTF14atg. We discuss several possibilities like interactions of the SN ejecta with the circumstellar medium and surface radioactivity from an He-ignited merger that may be able to account for the early UV emission in violent merger models.
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| 17. |
- Latour, M., et al.
(författare)
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Quantitative spectral analysis of the sdB star HD188112 : A helium-core white dwarf progenitor
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 585
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Tidskriftsartikel (refereegranskat)abstract
- Context. HD 188112 is a bright (V = 10 : 2 mag) hot subdwarf B (sdB) star with a mass too low to ignite core helium burning and is therefore considered a pre-extremely low-mass (ELM) white dwarf (WD). ELM WDs (M less than or similar to 0.3 M-circle dot) are He-core objects produced by the evolution of compact binary systems. Aims. We present in this paper a detailed abundance analysis of HD188112 based on high-resolution Hubble Space Telescope (HST) near-and far-ultraviolet spectroscopy. We also constrain the mass of the star's companion. Methods. We use hybrid non-LTE model atmospheres to fit the observed spectral lines, and to derive the abundances of more than a dozen elements and the rotational broadening of metallic lines. Results. We confirm the previous binary system parameters by combining radial velocities measured in our UV spectra with the previously published values. The system has a period of 0.60658584 days and a WD companion with M >= 0.70 M-circle dot. By assuming a tidally locked rotation combined with the projected rotational velocity (v sin i = 7.9 +/- 0.3 km s(-1)), we constrain the companion mass to be between 0.9 and 1.3 M-circle dot. We further discuss the future evolution of the system as a potential progenitor of an underluminous type Ia supernova. We measure abundances for Mg, Al, Si, P, S, Ca, Ti, Cr, Mn, Fe, Ni, and Zn, and for the trans-iron elements Ga, Sn, and Pb. In addition, we derive upper limits for the C, N, O elements and find HD188112 to be strongly depleted in carbon. We find evidence of non-LTE e ff ects on the line strength of some ionic species such as Si II and Ni II. The metallic abundances indicate that the star is metal-poor, with an abundance pattern most likely produced by diffusion effects.
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| 18. |
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| 19. |
- Magee, M. R., et al.
(författare)
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The type Iax supernova, SN 2015H A white dwarf deflagration candidate
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 589
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Tidskriftsartikel (refereegranskat)abstract
- We present results based on observations of SN 2015H which belongs to the small group of objects similar to SN 2002cx, otherwise known as type Iax supernovae. The availability of deep pre-explosion imaging allowed us to place tight constraints on the explosion epoch. Our observational campaign began approximately one day post-explosion, and extended over a period of about 150 days post maximum light, making it one of the best observed objects of this class to date. We find a peak magnitude of M-r = 17.27 +/- 0.07, and a (Delta m(15))(r) = 0.69 +/- 0.04. Comparing our observations to synthetic spectra generated from simulations of deflagrations of Chandrasekhar mass carbon-oxygen white dwarfs, we find reasonable agreement with models of weak deflagrations that result in the ejection of similar to 0.2 M-circle dot of material containing similar to 0.07 M-circle dot of Ni-56. The model light curve however, evolves more rapidly than observations, suggesting that a higher ejecta mass is to be favoured. Nevertheless, empirical modelling of the pseudo-bolometric light curve suggests that less than or similar to 0.6 M-circle dot of material was ejected, implying that the white dwarf is not completely disrupted, and that a bound remnant is a likely outcome.
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| 20. |
- Marquardt, Kai S., et al.
(författare)
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Type Ia supernovae from exploding oxygen-neon white dwarfs
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 580
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Tidskriftsartikel (refereegranskat)abstract
- Context: The progenitor problem of Type Ia supernovae (SNe Ia) is still unsolved. Most of these events are thought to be explosions of carbon-oxygen (CO) white dwarfs (WDs), but for many of the explosion scenarios, particularly those involving the externally triggered detonation of a sub-Chandrasekhar mass WD (sub-M-Ch, WD), there is also a possibility of having an oxygen-neon (ONe) WD as progenitor.Aims: We simulate detonations of ONe WDs and calculate synthetic observables from these models. The results are compared with detonations in CO WDs of similar mass and observational data of SNe Ia.Methods: We perform hydrodynamic explosion simulations of detonations in initially hydrostatic ONe WDs for a range of masses below the Chandrasekhar mass (M-Ch), followed by detailed nucleosynthetic postprocessing with a 384-isotope nuclear reaction network. The results are used to calculate synthetic spectra and light curves, which are then compared with observations of SNe Ia. We also perform binary evolution calculations to determine the number of SNe Ia involving ONe WDs relative to the number of other promising progenitor channels.Results: The ejecta structures of our simulated detonations in sub-M-Ch, ONe WDs are similar to those from CO WDs. There are, however, small systematic deviations in the mass fractions and the ejecta velocities. These lead to spectral features that are systematically less blueshifted. Nevertheless, the synthetic observables of our ONe WD explosions are similar to those obtained from CO models.Conclusions: Our binary evolution calculations show that a significant fraction (3-10%) of potential progenitor systems should contain an ONe WD. The comparison of our ONe models with our CO models of comparable mass (similar to 1.2 M-circle dot) shows that the less blueshifted spectral features fit the observations better, although they are too bright for normal SNe Ia.
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| 21. |
- Ohlmann, Sebastian T., et al.
(författare)
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The white dwarf's carbon fraction as a secondary parameter of Type la supernovae
- 2014
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 572, s. A57-
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Tidskriftsartikel (refereegranskat)abstract
- Context. Binary stellar evolution calculations predict that Chandrasekhar-mass carbon/oxygen white dwarfs (WDs) show a radially varying profile for the composition with a carbon depleted core. Many recent multi-dimensional simulations of Type Ia supernovae (SNe Ia), however, assume the progenitor WD has a homogeneous chemical composition. Aims. In this work, we explore the impact of different initial carbon profiles of the progenitor WD on the explosion phase and on synthetic observables in the Chandrasekhar-mass delayed detonation model. Spectra and light curves are compared to observations to judge the validity of the model. Methods. The explosion phase is simulated using the finite volume supernova code LEAFS, which is extended to treat different compositions of the progenitor WD. The synthetic observables are computed with the Monte Carlo radiative transfer code ARTIS. Results. Differences in binding energies of carbon and oxygen lead to a lower nuclear energy release for carbon depleted material; thus, the burning fronts that develop are weaker and the total nuclear energy release is smaller. For otherwise identical conditions, carbon depleted models produce less Ni-56. Comparing different models with similar Ni-56 yields shows lower kinetic energies in the ejecta for carbon depleted models, but only small differences in velocity distributions and line velocities in spectra. The light curve width-luminosity relation (WLR) obtained for models with differing carbon depletion is roughly perpendicular to the observed WLR, hence the carbon mass fraction is probably only a secondary parameter in the family of SNe Ia.
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| 22. |
- Pan, Y. -C, et al.
(författare)
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500 days of SN 2013dy : spectra and photometry from the ultraviolet to the infrared
- 2015
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 452:4, s. 4307-4325
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Tidskriftsartikel (refereegranskat)abstract
- SN 2013dy is a Type Ia supernova (SN Ia) for which we have compiled an extraordinary data set spanning from 0.1 to similar to 500 d after explosion. We present 10 epochs of ultraviolet (UV) through near-infrared (NIR) spectra with Hubble Space Telescope/Space Telescope Imaging Spectrograph, 47 epochs of optical spectra (15 of them having high resolution), and more than 500 photometric observations in the BVrRiIZYJH bands. SN 2013dy has a broad and slowly declining light curve (Delta m(15)(B)= 0.92 mag), shallow Si II lambda 6355 absorption, and a low velocity gradient. We detect strong C II in our earliest spectra, probing unburned progenitor material in the outermost layers of the SN ejecta, but this feature fades within a few days. The UV continuum of SN 2013dy, which is strongly affected by the metal abundance of the progenitor star, suggests that SN 2013dy had a relatively high-metallicity progenitor. Examining one of the largest single set of high-resolution spectra for an SN Ia, we find no evidence of variable absorption from circumstellar material. Combining our UV spectra, NIR photometry, and high-cadence optical photometry, we construct a bolometric light curve, showing that SN 2013dy had a maximum luminosity of 10.0(-3.8)(+4.8) x 10(42) erg s(-1). We compare the synthetic light curves and spectra of several models to SN 2013dy, finding that SN 2013dy is in good agreement with a solar-metallicity W7 model.
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| 23. |
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| 24. |
- Polshaw, J., et al.
(författare)
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A supernova distance to the anchor galaxy NGC 4258
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 580
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Tidskriftsartikel (refereegranskat)abstract
- The fortuitous occurrence of a type II-Plateau (IIP) supernova, SN 2014bc, in a galaxy for which distance estimates from a number of primary distance indicators are available provides a means with which to cross-calibrate the standardised candle method (SCM) for type IIP SNe. By applying calibrations from the literature we find distance estimates in line with the most precise measurement to NGC 4258 based on the Keplerian motion of masers (7.6 +/- 0.23 Mpc), albeit with significant scatter. We provide an alternative local SCM calibration by only considering type IIP SNe that have occurred in galaxies for which a Cepheid distance estimate is available. We find a considerable reduction in scatter (sigma(I) = 0.16 mag), but note that the current sample size is limited. Applying this calibration, we estimate a distance to NGC 4258 of 7.08 +/- 0.86 Mpc.
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| 25. |
- Sasdelli, Michele, et al.
(författare)
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A metric space for Type Ia supernova spectra : a new method to assess explosion scenarios
- 2017
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 466:4, s. 3784-3809
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Tidskriftsartikel (refereegranskat)abstract
- Over the past years, Type Ia supernovae (SNe Ia) have become a major tool to determine the expansion history of the Universe, and considerable attention has been given to, both, observations and models of these events. However, until now, their progenitors are not known. The observed diversity of light curves and spectra seems to point at different progenitor channels and explosion mechanisms. Here, we present a newway to compare model predictions with observations in a systematic way. Our method is based on the construction of a metric space for SN Ia spectra by means of linear principal component analysis, taking care of missing and/or noisy data, and making use of partial least-squares regression to find correlations between spectral properties and photometric data. We investigate realizations of the three major classes of explosion models that are presently discussed: delayed-detonation Chandrasekharmass explosions, sub-Chandrasekhar-mass detonations and double-degenerate mergers, and compare them with data. We show that in the principal component space, all scenarios have observed counterparts, supporting the idea that different progenitors are likely. However, all classes of models face problems in reproducing the observed correlations between spectral properties and light curves and colours. Possible reasons are briefly discussed.
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