| 1. |
- Harutyunyan, A. H., et al.
(författare)
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ESC supernova spectroscopy of non-ESC targets
- 2008
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 488:1, s. 383-399
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Forskningsöversikt (refereegranskat)abstract
- Aims. We present the spectra of 36 supernovae (SNe) of various types, obtained by the European Supernova Collaboration. Because of the spectral classification and the phase determination at their discovery the SNe did not warrant further study, and the spectra we present are the only ones available for the respective objects. In this paper we present and discuss this material using a new software for the automated classification of SNe spectra. Methods. As a validation of the software, we verify the classification and phase estimate reported for these objects in their discovery/classification circulars. For the comparison, the software uses the library of template spectra of Padova-Asiago Supernova Archive (ASA). Results. For each spectrum of our sample we present a brief, individual discussion, highlighting the main characteristics and possible peculiarities. The comparison with ASA spectra confirms the previous classification of all objects and refines the age estimates. For our software, we determine numerical limits of ""safe"" spectral classification and the uncertainties of the phase determination.
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| 2. |
- Pastorello, A., et al.
(författare)
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A giant outburst two years before the core-collapse of a massive star
- 2007
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 447:7146, s. 829-832
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Tidskriftsartikel (refereegranskat)abstract
- The death of massive stars produces a variety of supernovae, which are linked to the structure of the exploding stars(1,2). The detection of several precursor stars of type II supernovae has been reported ( see, for example, ref. 3), but we do not yet have direct information on the progenitors of the hydrogen-deficient type Ib and Ic supernovae. Here we report that the peculiar type Ib supernova SN 2006jc is spatially coincident with a bright optical transient(4) that occurred in 2004. Spectroscopic and photometric monitoring of the supernova leads us to suggest that the progenitor was a carbon-oxygen Wolf - Rayet star embedded within a helium-rich circumstellar medium. There are different possible explanations for this pre-explosion transient. It appears similar to the giant outbursts of luminous blue variable stars (LBVs) of 60 - 100 solar masses(5), but the progenitor of SN 2006jc was helium- and hydrogen-deficient ( unlike LBVs). An LBV-like outburst of a Wolf - Rayet star could be invoked, but this would be the first observational evidence of such a phenomenon. Alternatively, a massive binary system composed of an LBV that erupted in 2004, and a Wolf - Rayet star exploding as SN 2006jc, could explain the observations.
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| 3. |
- Young, D. R., et al.
(författare)
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Two type Ic supernovae in low-metallicity, dwarf galaxies : diversity of explosions
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 512, s. 70-
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Tidskriftsartikel (refereegranskat)abstract
- Aims: The aim of this paper is to discuss the nature of two type Ic supernovae SN 2007bg and SN 2007bi and their host galaxies. Both supernovae were discovered in wide-field, non-targeted surveys and are found to be associated with sub-luminous blue dwarf galaxies identified in SDSS images. Methods: We present BVRI photometry and optical spectroscopy of SN 2007bg and SN 2007bi and their host galaxies. Their lightcurves and spectra are compared to those of other type Ic SNe and analysis of these data provides estimates of the energetics, total ejected masses and synthesised mass of 56Ni. Detection of the host galaxy emission lines allows for metallicity measurements. Results: Neither SNe 2007bg nor 2007bi were found in association with an observed GRB, but from estimates of the metallicities of their host-galaxies they are found to inhabit similar low-metallicity environments as GRB associated supernovae. The radio-bright SN 2007bg is hosted by an extremely sub-luminous galaxy of magnitude MB = -12.4 ± 0.6 mag and an estimated oxygen abundance of 12+log(O/H) = 8.18 ± 0.17 (on the Pettini & Pagel 2004 scale). The early lightcurve evolution of SN 2007bg matches the fast-pace decline of SN 1994I giving it one of the fastest post-maximum decline rates of all broad-lined type Ic supernovae known to date and, when combined with its high expansion velocities, a high kinetic energy to ejected mass ratio (EK/Mej~2.7). We also show that SN 2007bi is possibly the most luminous type Ic known, reaching a peak magnitude of MR ~ -21.3 mag and displays a remarkably slow decline, following the radioactive decay rate of 56Co to 56Fe throughout the course of its observed lifetime. SN 2007bi also displays an extreme longevity in its spectral evolution and is still not fully nebular at approximately one year post-maximum brightness. From a simple model of the bolometric light curve of SN 2007bi we estimate a total ejected 56Ni mass of MNi = 3.5-4.5 M_ȯ, the largest 56Ni mass measured in the ejecta of a supernova to date. There are two models that could explain the high luminosity and large ejected 56Ni mass. One is a pair-instability supernova (PISN) which has been predicted to occur for massive stars at low metallicities. We measure the host galaxy metallicity of SN 2007bi to be 12+log(O/H) = 8.15 ± 0.15 (on the McGaugh 1991 scale) which is somewhat high to be consistent with the PISN model. An alternative is the core-collapse of a C+O star of 20-40 Mȯ which is the core of a star of originally 50-100 Mȯ.
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| 4. |
- Pastorello, A., et al.
(författare)
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ESC and KAIT observations of the transitional type Ia SN 2004eo
- 2007
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 377:4, s. 1531-1552
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Tidskriftsartikel (refereegranskat)abstract
- We present optical and infrared observations of the unusual Type Ia supernova (SN) 2004eo. The light curves and spectra closely resemble those of the prototypical SN 1992A, and the luminosity at maximum (M-B = -19.08) is close to the average for a Type Ia supernova (SN Ia). However, the ejected Ni-56 mass derived by modelling the bolometric light curve (about 0.45M(circle dot)) lies near the lower limit of the Ni-56 mass distribution observed in normal SNe Ia. Accordingly, SN 2004eo shows a relatively rapid post-maximum decline in the light curve [Delta m(15)(B)(true) = 1.46], small expansion velocities in the ejecta and a depth ratio Si II lambda 5972/ Si II lambda 6355 similar to that of SN 1992A. The physical properties of SN 2004eo cause it to fall very close to the boundary between the faint, low-velocity gradient and high-velocity gradient subgroups proposed by Benetti et al. Similar behaviour is seen in a few other SNe Ia. Thus, there may in fact exist a few SNe Ia with intermediate physical properties.
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| 5. |
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| 6. |
- Pastorello, A., et al.
(författare)
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Multiple major outbursts from a restless luminous blue variable in NGC 3432
- 2010
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 408:1, s. 181-198
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Tidskriftsartikel (refereegranskat)abstract
- We present new photometric and spectroscopic observations of an unusual luminous blue variable (LBV) in NGC 3432, covering three major outbursts in 2008 October, 2009 April and 2009 November. Previously, this star experienced an outburst also in 2000 (known as SN 2000ch). During outbursts the star reached an absolute magnitude between -12.1 and -12.8. Its spectrum showed H, He I and Fe II lines with P-Cygni profiles during and soon after the eruptive phases, while only intermediate-width lines in pure emission (including He II lambda 4686) were visible during quiescence. The fast-evolving light curve soon after the outbursts, the quasi-modulated light curve, the peak magnitude and the overall spectral properties are consistent with multiple episodes of variability of an extremely active LBV. However, the widths of the spectral lines indicate unusually high wind velocities (1500-2800 km s-1), similar to those observed in Wolf-Rayet stars. Although modulated light curves are typical of LBVs during the S-Dor variability phase, the luminous maxima and the high frequency of outbursts are unexpected in S-Dor variables. Such extreme variability may be associated with repeated ejection episodes during a giant eruption of an LBV. Alternatively, it may be indicative of a high level of instability shortly preceding the core-collapse or due to interaction with a massive, binary companion. In this context, the variable in NGC 3432 shares some similarities with the famous stellar system HD 5980 in the Small Magellanic Cloud, which includes an erupting LBV and an early Wolf-Rayet star.
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| 7. |
- Pastorello, A., et al.
(författare)
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SN 2009E : a faint clone of SN 1987A
- 2012
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 537
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Tidskriftsartikel (refereegranskat)abstract
- Context. 1987A-like events form a rare sub-group of hydrogen-rich core-collapse supernovae that are thought to originate from the explosion of blue supergiant stars. Although SN 1987A is the best known supernova, very few objects of this group have been discovered and, hence, studied. Aims. In this paper we investigate the properties of SN 2009E, which exploded in a relatively nearby spiral galaxy (NGC 4141) and that is probably the faintest 1987A-like supernova discovered so far. We also attempt to characterize this subgroup of core-collapse supernovae with the help of the literature and present new data for a few additional objects. Methods. The lack of early-time observations from professional telescopes is compensated by frequent follow-up observations performed by a number of amateur astronomers. This allows us to reconstruct a well-sampled light curve for SN 2009E. Spectroscopic observations which started about 2 months after the supernova explosion, highlight significant differences between SN 2009E and the prototypical SN 1987A. Modelling the data of SN 2009E allows us to constrain the explosion parameters and the properties of the progenitor star, and compare the inferred estimates with those available for the similar SNe 1987A and 1998A. Results. The light curve of SN 2009E is less luminous than that of SN 1987A and the other members of this class, and the maximum light curve peak is reached at a slightly later epoch than in SN 1987A. Late-time photometric observations suggest that SN 2009E ejected about 0.04 M-circle dot of Ni-56, which is the smallest Ni-56 mass in our sample of 1987A-like events. Modelling the observations with a radiation hydrodynamics code, we infer for SN 2009E a kinetic plus thermal energy of about 0.6 foe, an initial radius of similar to 7x10(12) cm and an ejected mass of similar to 19 M-circle dot. The photospheric spectra show a number of narrow (v approximate to 1800 km s(-1)) metal lines, with unusually strong Ba II lines. The nebular spectrum displays narrow emission lines of H, Na I, [Ca II] and [O I], with the [O I] feature being relatively strong compared to the [Ca II] doublet. The overall spectroscopic evolution is reminiscent of that of the faint Ni-56-poor type II-plateau supernovae. This suggests that SN 2009E belongs to the low-luminosity, low Ni-56 mass, low-energy tail in the distribution of the 1987A-like objects in the same manner as SN 1997D and similar events represent the faint tail in the distribution of physical properties for normal type II-plateau supernovae.
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| 8. |
- Spiro, S., et al.
(författare)
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Low luminosity Type II supernovae - II. Pointing towards moderate mass precursors
- 2014
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 439:3, s. 2873-2892
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Tidskriftsartikel (refereegranskat)abstract
- We present new data for five underluminous Type II-plateau supernovae (SNe IIP), namely SN 1999gn, SN 2002gd, SN 2003Z, SN 2004eg and SN 2006ov. This new sample of low-luminosity SNe IIP (LL SNe IIP) is analysed together with similar objects studied in the past. All of them show a flat light-curve plateau lasting about 100 d, an underluminous late-time exponential tail, intrinsic colours that are unusually red, and spectra showing prominent and narrow P Cygni lines. A velocity of the ejected material below 10(3) km s(-1) is inferred from measurements at the end of the plateau. The Ni-56 masses ejected in the explosion are very small (< 10(-2) M-circle dot). We investigate the correlations among Ni-56 mass, expansion velocity of the ejecta and absolute magnitude in the middle of the plateau, confirming the main findings of Hamuy, according to which events showing brighter plateau and larger expansion velocities are expected to produce more Ni-56. We propose that these faint objects represent the LL tail of a continuous distribution in parameters space of SNe IIP. The physical properties of the progenitors at the explosion are estimated through the hydrodynamical modelling of the observables for two representative events of this class, namely SN 2005cs and SN 2008in. We find that the majority of LL SNe IIP, and quite possibly all, originate in the core collapse of intermediate-mass stars, in the mass range 10-15 M-circle dot.
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| 9. |
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| 10. |
- Stanishev, Vallery, et al.
(författare)
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SN 2003du: 480 days in the life of a normal type Ia supernova
- 2007
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 469:2, s. 645-661
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Tidskriftsartikel (refereegranskat)abstract
- Aims.We present a study of the optical and near-infrared (NIR) properties of the Type Ia Supernova (SN Ia) 2003du.Methods: An extensive set of optical and NIR photometry and low-resolution long-slit spectra was obtained using a number of facilities. The observations started 13 days before B-band maximum light and continued for 480 days with exceptionally good time sampling. The optical photometry was calibrated through the S-correction technique.Results: The {UBVRIJHK} light curves and the color indices of SN 2003du closely resemble those of normal SNe Ia. SN 2003du reached a B-band maximum of 13.49 ± 0.02 mag on JD2 452 766.38 ± 0.5. We derive a B-band stretch parameter of 0.988 ±0.003, which corresponds to Δ m15=1.02 ±0.05, indicative of a SN Ia of standard luminosity. The reddening in the host galaxy was estimated by three methods, and was consistently found to be negligible. Using an updated calibration of the V and {JHK} absolute magnitudes of SNe Ia, we find a distance modulus μ=32.79±0.15 mag to the host galaxy, UGC 9391. We measure a peak {uvoir} bolometric luminosity of 1.35(±0.20)×1043 erg s-1 and Arnett's rule implies that M56Ni≃0.68 ±0.14 Mȯ of 56Ni was synthesized during the explosion. Modeling of the {uvoir} bolometric light curve also indicates M56Ni in the range 0.6-0.8 Mȯ. The spectral evolution of SN 2003du at both optical and NIR wavelengths also closely resembles normal SNe Ia. In particular, the Si II ratio at maximum R(Si II) = 0.22 ±0.02 and the time evolution of the blueshift velocities of the absorption line minima are typical. The pre-maximum spectra of SN 2003du showed conspicuous high-velocity features in the Ca II H&K doublet and infrared triplet, and possibly in Si II λ6355, lines. We compare the time evolution of the profiles of these lines with other well-observed SNe Ia and we suggest that the peculiar pre-maximum evolution of Si II λ6355 line in many SNe Ia is due to the presence of two blended absorption components.
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