727 research outputs found
Luminous Blue Variables as the progenitors of supernovae with quasi-periodic radio modulations
The interaction between supernova ejecta and circumstellar matter, arising
from previous episodes of mass loss, provides us with a means with which to
constrain the progenitors of supernovae. Radio observations of a number of
supernovae show quasi-periodic deviations from a strict power-law decline at
late times. Although several possibilities have been put forward to explain
these modulations, no single explanation has proven to be entirely
satisfactory. Here we suggest that Luminous Blue Variables undergoing S-Doradus
type variations give rise to enhanced phases of mass loss which are imprinted
on the immediate environment of the exploding star as a series of density
enhancements. The variations in mass loss arise from changes in the ionization
balance of Fe, the dominant ion that drives the wind. With this idea, we find
that both the recurrence timescale of the variability, as well as the amplitude
of the modulations are in line with the observations. Our scenario thus
provides a natural, single-star explanation for the observed behaviour that is,
in fact, expected on theoretical grounds.Comment: A&A Letters (accepted
Detecting the signatures of helium in type Iax supernovae
Recent studies have argued that the progenitor system of type Iax supernovae
must consist of a carbon-oxygen white dwarf accreting from a helium star
companion. Based on existing explosion models invoking the pure deflagration of
carbon-oxygen white dwarfs, we investigate the likelihood of producing spectral
features due to helium in type Iax supernovae. From this scenario, we select
those explosion models producing ejecta and Ni masses that are broadly
consistent with those estimated for type Iax supernovae (0.014 -
0.478~ and - 0.183~, respectively). To this
end, we present a series of models of varying luminosities (~mag) with helium abundances accounting for up to
36\% of the ejecta mass, and covering a range of epochs beginning a few
days before Bband maximum to approximately two weeks after maximum. We find
that the best opportunity for detecting \ion{He}{i} features is at
near-infrared wavelengths, and in the post-maximum spectra of the fainter
members of this class. We show that the optical spectrum of SN~2007J is
potentially consistent with a large helium content (a few 10),
but argue that current models of accretion and material stripping from a
companion struggle to produce compatible scenarios. We also investigate the
presence of helium in all objects with near-infrared spectra. We show that
SNe~2005hk, 2012Z, and 2015H contain either no helium or their helium
abundances are constrained to much lower values
(10). Our results demonstrate the differences in
helium content among type Iax supernovae, perhaps pointing to different
progenitor channels. Either SN~2007J is an outlier in terms of its progenitor
system, or it is not a true member of the type Iax supernova class.Comment: 15 pages, 12 figures, 2 tables. Accepted for publication in Astronomy
and Astrophysic
SN 2005 gj: Evidence for LBV supernovae progenitors?
There has been mounting observational evidence in favour of Luminous Blue
Variables (LBVs) being the direct progenitors of supernovae. Here we present
possibly the most convincing evidence yet for such progenitors. We find
multiple absorption component P-Cygni profiles of hydrogen and helium in the
spectrum of SN 2005gj, which we interpret as being an imprint of the
progenitors mass-loss history. Such profiles have previously only been detected
in Luminous Blue Variables. This striking resemblance of the profiles, along
with wind velocities and periods consistent with LBV's leads us to connect SN
2005gj to an LBV progenitor.Comment: Accepted as a letter to A&A, 4 pages,3 figure
The nebular spectra of SN 2012aw and constraints on stellar nucleosynthesis from oxygen emission lines
We present nebular phase optical and near-infrared spectroscopy of the Type
IIP supernova SN 2012aw combined with NLTE radiative transfer calculations
applied to ejecta from stellar evolution/explosion models. Our spectral
synthesis models generally show good agreement with the ejecta from a MZAMS =
15 Msun progenitor star. The emission lines of oxygen, sodium, and magnesium
are all consistent with the nucleosynthesis in a progenitor in the 14 - 18 Msun
range. We also demonstrate how the evolution of the oxygen cooling lines of [O
I] 5577 A, [O I] 6300 A, and [O I] 6364 A can be used to constrain the mass of
oxygen in the non-molecularly cooled ashes to < 1 Msun, independent of the
mixing in the ejecta. This constraint implies that any progenitor model of
initial mass greater than 20 Msun would be difficult to reconcile with the
observed line strengths. A stellar progenitor of around MZAMS = 15 Msun can
consistently explain the directly measured luminosity of the progenitor star,
the observed nebular spectra, and the inferred pre-supernova mass-loss rate. We
conclude that there is still no convincing example of a Type IIP explosion
showing the nucleosynthesis expected from a MZAMS > 20 Msun progenitor.Comment: Accepted for publication in MNRA
Applying the expanding photosphere and standardized candle methods to Type II-Plateau supernovae at cosmologically significant redshifts: the distance to SN 2013eq
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.Comment: 12 pages, 4 figures, accepted by A&
Spectropolarimetry of Type II supernovae (I) Sample, observational data and interstellar polarization
We investigate polarization spectra of hydrogen-rich core-collapse supernovae
(Type~II SNe). The polarization signal from SNe contains two independent
components: intrinsic SN polarization and interstellar polarization (ISP). From
these components, we can study the SN explosion geometry and the dust
properties in their host galaxies or in the Milky Way. In this first paper,
using a new improved method, we investigate the properties of the ISP
components of 11 well-observed Type~II SNe. As a result of our analysis, we
find that 10 out of these 11 SNe showed a steady ISP component with a
polarization degree \%, while one SN was consistent with zero
ISP. As for the wavelength dependence, SN~2001dh (and possibly SN~2012aw)
showed a non-Milky-Way-like ISP likely originating from the interstellar dust
in their respective host galaxies: their polarization maxima were located at
short wavelengths (~\AA). Similar results have been obtained
previously for highly reddened SNe. The majority of the SNe in our sample had
too large uncertainties in the wavelength dependence of their ISP components to
consider them further. Our work demonstrates that, by applying this method to a
larger SN sample, further investigation of the ISP component of the SN
polarization can provide new opportunities to study interstellar dust
properties in external galaxies.Comment: 35 pages, 36 figures, accepted for publication in A&
Early-time Spitzer observations of the type II-Plateau supernova, 2004dj
We present mid-infrared observations with the Spitzer Space Telescope of the
nearby type II-P supernova, SN 2004dj, at epochs of 89 to 129 days. We have
obtained the first mid-IR spectra of any supernova apart from SN 1987A. A
prominent [NiII] 6.64 micron line is observed, from which we deduce that the
mass of stable nickel must be at least 2.2e10(-4) Msun. We also observe the red
wing of the CO-fundamental band. We relate our findings to possible progenitors
and favour an evolved star, most likely a red supergiant, with a probable
initial mass between ~10 and 15 Msun.Comment: ApJ Letters (accepted
Modelling the early time behaviour of type Ia supernovae: effects of the 56Ni distribution
Recent studies have demonstrated the diversity in type Ia supernovae (SNe Ia)
at early times and highlighted a need for a better understanding of the
explosion physics as manifested by observations soon after explosion. To this
end, we present a Monte Carlo code designed to model the light curves of
radioactively driven, hydrogen-free transients from explosion to approximately
maximum light. In this initial study, we have used a parametrised description
of the ejecta in SNe Ia, and performed a parameter study of the effects of the
Ni distribution on the observed colours and light curves for a fixed
Ni mass of 0.6 . For a given density profile, we find that
models with Ni extending throughout the entirety of the ejecta are
typically brighter and bluer shortly after explosion. Additionally, the shape
of the density profile itself also plays an important role in determining the
shape, rise time, and colours of observed light curves. We find that the
multi-band light curves of at least one SNe Ia (SN 2009ig) are inconsistent
with less extended Ni distributions, but show good agreement with models
that incorporate Ni throughout the entire ejecta. We further demonstrate
that comparisons with full colour light curves are powerful tools in
discriminating various Ni distributions, and hence explosion models.Comment: 14 pages, 8 figures, 2 tables. Minor changes in notation to match
published version in Astronomy & Astrophysic
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