| 1. |
- Bersten, Melina C., et al.
(författare)
-
THE TYPE IIb SUPERNOVA 2011dh FROM A SUPERGIANT PROGENITOR
- 2012
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 757:1
-
Tidskriftsartikel (refereegranskat)abstract
- A set of hydrodynamical models based on stellar evolutionary progenitors is used to study the nature of SN 2011dh. Our modeling suggests that a large progenitor star-with R similar to 200 R-circle dot-is needed to reproduce the early light curve (LC) of SN 2011dh. This is consistent with the suggestion that the yellow super-giant star detected at the location of the supernova (SN) in deep pre-explosion images is the progenitor star. From the main peak of the bolometric LC and expansion velocities, we constrain the mass of the ejecta to be approximate to 2 M-circle dot, the explosion energy to be E = (6-10) x 10(50) erg, and the Ni-56 mass to be approximately 0.06 M-circle dot. The progenitor star was composed of a helium core of 3-4 M-circle dot and a thin hydrogen-rich envelope of approximate to 0.1M(circle dot) with a main-sequence mass estimated to be in the range of 12-15 M-circle dot. Our models rule out progenitors with helium-core masses larger than 8 M-circle dot, which correspond to M-ZAMS greater than or similar to 25M(circle dot). This suggests that a single star evolutionary scenario for SN 2011dh is unlikely.
|
|
| 2. |
- Clark, Peter, et al.
(författare)
-
LSQ13ddu : a rapidly evolving stripped-envelope supernova with early circumstellar interaction signatures
- 2020
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 492:2, s. 2208-2228
-
Tidskriftsartikel (refereegranskat)abstract
- This paper describes the rapidly evolving and unusual supernova LSQ13ddu, discovered by the La Silla-QUEST survey. LSQ13ddu displayed a rapid rise of just 4.8 +/- 0.9 d to reach a peak brightness of -19.70 +/- 0.02 mag in the LSQgr band. Early spectra of LSQ13ddu showed the presence of weak and narrow He I features arising from interaction with circumstellar material (CSM). These interaction signatures weakened quickly, with broad features consistent with those seen in stripped-envelope SNe becoming dominant around two weeks after maximum. The narrow He I velocities are consistent with the wind velocities of luminous blue variables but its spectra lack the typically seen hydrogen features. The fast and bright early light curve is inconsistent with radioactive Ni-56 powering but can be explained through a combination of CSM interaction and an underlying Ni-56 decay component that dominates the later time behaviour of LSQ13ddu. Based on the strength of the underlying broad features, LSQ13ddu appears deficient in He compared to standard SNe Ib.
|
|
| 3. |
- Elias-Rosa, Nancy, et al.
(författare)
-
The Type IIn Supernova SN 2010bt : The Explosion of a Star in Outburst
- 2018
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 860:1
-
Tidskriftsartikel (refereegranskat)abstract
- It is well known that massive stars (M > 8M(circle dot)) evolve up to the collapse of the stellar core, resulting in most cases in a supernova (SN) explosion. Their heterogeneity is related mainly to different configurations of the progenitor star at the moment of the explosion and to their immediate environments. We present photometry and spectroscopy of SN. 2010bt, which was classified as a Type. IIn. SN from a spectrum obtained soon after discovery and was observed extensively for about 2 months. After the seasonal interruption owing to its proximity to the Sun, the SN was below the detection threshold, indicative of a rapid luminosity decline. We can identify the likely progenitor with a very luminous star (log L/L-circle dot approximate to 7) through comparison of Hubble Space Telescope images of the host galaxy prior to explosion with those of the SN obtained after maximum light. Such a luminosity is not expected for a quiescent star, but rather for a massive star in an active phase. This progenitor candidate was later confirmed via images taken in 2015 (similar to 5 yr post-discovery), in which no bright point source was detected at the SN position. Given these results and the SN behavior, we conclude that SN. 2010bt was likely a Type IIn SN and that its progenitor was a massive star that experienced an outburst shortly before the final explosion, leading to a dense H-rich circumstellar environment around the SN progenitor.
|
|
| 4. |
- Gerardy, Christopher L., et al.
(författare)
-
Signatures of Delayed Detonation, Asymmetry, and Electron Capture in the Mid-Infrared Spectra of Supernovae 2003hv and 2005df
- 2007
-
Ingår i: The Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 661:2, s. 995-1012
-
Tidskriftsartikel (refereegranskat)abstract
- We present mid-infrared (5.2-15.2 μm) spectra of the Type Ia supernovae (SNe Ia) 2003hv and 2005df observed with the Spitzer Space Telescope. These are the first observed mid-infrared spectra of thermonuclear supernovae, and show strong emission from fine-structure lines of Ni, Co, S, and Ar. The detection of Ni emission in SN 2005df 135 days after the explosion provides direct observational evidence of high-density nuclear burning forming a significant amount of stable Ni in a SN Ia. The SN 2005df Ar lines also exhibit a two-pronged emission profile, implying that the Ar emission deviates significantly from spherical symmetry. The spectrum of SN 2003hv also shows signs of asymmetry, exhibiting blueshifted [Co III], which matches the blueshift of [Fe II ] lines in nearly coeval near-infrared spectra. Finally, local thermodynamic equilibrium abundance estimates for the yield of radioactive 56Ni give M56Ni~0.5 Msolar, for SN 2003hv, but only M56Ni~0.13-0.22 Msolar for the apparently subluminous SN 2005df, supporting the notion that the luminosity of SNe Ia is primarily a function of the radioactive 56Ni yield. The observed emission-line profiles in the SN 2005df spectrum indicate a chemically stratified ejecta structure, which matches the predictions of delayed detonation (DD) models, but is entirely incompatible with current three-dimensional deflagration models. Furthermore, the degree that this layering persists to the innermost regions of the supernova is difficult to explain even in a DD scenario, where the innermost ejecta are still the product of deflagration burning. Thus, while these results are roughly consistent with a delayed detonation, it is clear that a key piece of physics is still missing from our understanding of the earliest phases of SN Ia explosions.
|
|
| 5. |
|
|
| 6. |
- Kotak, Rubina, et al.
(författare)
-
A new look at the pulsating DB white dwarf GD 358: Line-of-sight velocity measurements and constraints on model atmospheres
- 2003
-
Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 397, s. 1043-1055
-
Tidskriftsartikel (refereegranskat)abstract
- We report on our findings of the bright, pulsating, helium atmospherewhite dwarf GD 358, based on time-resolved optical spectrophotometry. Weidentify 5 real pulsation modes and at least 6 combination modes atfrequencies consistent with those found in previous observations. Themeasured Doppler shifts from our spectra show variations with amplitudesof up to 5.5 km s-1 at the frequencies inferred from the fluxvariations. We conclude that these are variations in the line-of-sightvelocities associated with the pulsational motion. We use the observedflux and velocity amplitudes and phases to test theoretical predictionswithin the convective driving framework, and compare these with similarobservations of the hydrogen atmosphere white dwarf pulsators (DAVs).The wavelength dependence of the fractional pulsation amplitudes(chromatic amplitudes) allows us to conclude that all five real modesshare the same spherical degree, most likely, l=1. This is consistentwith previous identifications based solely on photometry. We find that ahigh signal-to-noise mean spectrum on its own is not enough to determinethe atmospheric parameters and that there are small but significantdiscrepancies between the observations and model atmospheres. The sourceof these remains to be identified. While we infer Teff =24 kKand log g ~ 8.0 from the mean spectrum, the chromatic amplitudes, whichare a measure of the derivative of the flux with respect to thetemperature, unambiguously favour a higher effective temperature, 27 kK,which is more in line with independent determinations from ultra-violetspectra.The data presented herein were obtained at the W.M. Keck Observatory,which is operated as a scientific partnership among the CaliforniaInstitute of Technology, the University of California and the NationalAeronautics and Space Administration. The Observatory was made possibleby the generous financial support of the W.M. Keck Foundation.
|
|
| 7. |
- Kotak, Rubina, et al.
(författare)
-
A puzzling periodicity in the pulsating DA white dwarf G 117-B15A
- 2004
-
Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 413, s. 301-308
-
Tidskriftsartikel (refereegranskat)abstract
- We present time-resolved optical spectrophotometry of the pulsatinghydrogen atmosphere (DA) white dwarf G 117-B15A. We find threeperiodicities in the pulsation spectrum (215 s, 272 s, and 304 s) all ofwhich have been found in earlier studies. By comparing the fractionalwavelength dependence of the pulsation amplitudes (chromatic amplitudes)with models, we confirm a previous report that the strongest mode, at215 s, has ℓ=1. The chromatic amplitude for the 272 s mode is verypuzzling, showing an increase in fractional amplitude with wavelengththat cannot be reproduced by the models for any ℓ at opticalwavelengths. Based on archival HST data, we show that while thebehaviour of the 215 s mode at ultra-violet wavelengths is as expectedfrom models, the weird behaviour of the 272 s periodicity is notrestricted to optical wavelengths in that it fails to show the expectedincrease in fractional amplitude towards shorter wavelengths. We discusspossible causes for the discrepancies found for the 272 s variation, butfind that all are lacking, and conclude that the nature of thisperiodicity remains unclear.Based in part on data obtained at the W.M. Keck Observatory, which isoperated as a scientific partnership among the California Institute ofTechnology, the University of California and the National Aeronauticsand Space Administration. The Observatory was made possible by thegenerous financial support of the W.M. Keck Foundation.
|
|
| 8. |
|
|
| 9. |
- Kotak, Rubina
(författare)
-
Inside Pulsating White Dwarfs: Clues from time-resolved spectroscopy
- 2002
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Several analyses using time-resolved optical spectrocopy of pulsating white dwarfs are presented. The data have been put to a number of uses. First, line-of-sight velocities associated with the pulsations have been measured in three hydrogen-atmosphere white dwarfs (DAVs), bringing the total number of such measurements up to five. They have also been measured for the first time in a pulsating helium-atmosphere white dwarf (DBV). The relative velocity to flux amplitude ratios are compared with theoretical expectations based on theories of mode driving via convection. Secondly, the fractional, wavelength-dependent pulsation amplitudes (``chromatic amplitudes'') have been used to identify the spherical degree of the pulsation modes. Consistent results are obtained for objects with mode identifications based solely on photometry. This shows that the technique works. The new mode identifications can be used in pulsation models to constrain the asteroseismological solution of the white dwarf in question. The chromatic amplitudes have also been used to understand the shortcomings of currently used model atmospheres. These are most likely due to the lack of a realistic treatement of convection. Combining all the available information from data such as ours is a first step towards constraining atmospheric properties in a convectionally unstable environment from an observational perspective. In the final chapter an attempt is made to explain the observed quasi-periodic variations in the rotationally split modes of certain pulsators.
|
|
| 10. |
|
|
