49 research outputs found
A reconnaissance of the possible donor stars to the Kepler supernova
The identity of Type Ia supernova progenitors remains a mystery, with various
lines of evidence pointing towards either accretion from a non-degenerate
companion, or the rapid merger of two degenerate stars leading to the
thermonuclear destruction of a white dwarf. In this paper we spectroscopically
scrutinize 24 of the brightest stars residing in the central 38" x 38" of the
SN 1604 (Kepler) supernova remnant to search for a possible surviving companion
star. We can rule out, with high certainty, a red giant companion star - a
progenitor indicated by some models of the supernova remnant. Furthermore, we
find no star that exhibits properties uniquely consistent with those expected
of a donor star down to L>10Lsun. While the distribution of star properties
towards the remnant are consistent with unrelated stars, we identify the most
promising candidates for further astrometric and spectroscopic follow-up. Such
a program would either discover the donor star, or place strong limits on
progenitor systems to luminosities with L<<Lsun.Comment: accepted by Ap
The rotation of surviving companion stars after type Ia supernova explosions in the WD+MS scenario
In the SD scenario of SNe Ia the companion survives the SN explosion and thus
should be visible near the center of the SN remnant and may show some unusual
features. A promising approach to test progenitor models of SNe Ia is to search
for the companion in SNRs. Here we present the results of 3D hydrodynamics
simulations of the interaction between the SN Ia blast wave and a MS companion
taking into consideration its orbital motion and spin. The primary goal of this
work is to investigate the rotation of surviving companions after SN Ia
explosions in the WD+MS scenario. We use Eggleton's code including the
optically thick accretion wind model to obtain realistic models of companions.
The impact of the SN blast wave on these companions is followed in 3D
hydrodynamic simulations employing the SPH code GADGET3. We find that the
rotation of the companion does not significantly affect the amount of stripped
mass and the kick velocity caused by the SN impact. However, in our
simulations, the rotational velocity of the companion is significantly reduced
to about 14% to 32% of its pre-explosion value due to the expansion of the
companion and the fact that 55%-89% of the initial angular momentum is carried
away by the stripped matter. Compared with the observed rotational velocity of
the presumed companion star of Tycho's SN, Tycho G, of 6 km/s the final
rotational velocity we obtain is still higher by at least a factor of two.
Whether this difference is significant, and may cast doubts on the suggestion
that Tycho G is the companion of SN 1572, has to be investigated in future
studies. Based on binary population synthesis results we present, for the first
time, the expected distribution of rotational velocities of companions after
the explosion which may provide useful information for the identification of
the surviving companion in observational searches in other historical SNRs.Comment: 13 pages, 15 figures, accepted for publication by Astronomy and
Astrophysic
Type Iax SNe as a few-parameter family
We present direct spectroscopic modeling of five Type Iax supernovae (SNe)
with the one dimensional Monte Carlo radiative transfer code TARDIS. The
abundance tomography technique is used to map the chemical structure and
physical properties of the SN atmosphere. Through via fitting of multiple
spectral epochs with self-consistent ejecta models, we can then constrain the
location of some elements within the ejecta. The synthetic spectra of the
best-fit models are able to reproduce the flux continuum and the main
absorption features in the whole sample. We find that the mass fractions of
IGEs and IMEs show a decreasing trend toward the outer regions of the
atmospheres using density profiles similar to those of deflagration models in
the literature. Oxygen is the only element, which could be dominant at higher
velocities. The stratified abundance structure contradicts the well-mixed
chemical profiles predicted by pure deflagration models. Based on the derived
densities and abundances, a template model atmosphere is created for the SN Iax
class and compared to the observed spectra. Free parameters are the scaling of
the density profile, the velocity shift of the abundance template, and the peak
luminosity. The results of this test support the idea that all SNe Iax can be
described by a similar internal structure, which argues for a common origin of
this class of explosions.Comment: 21 pages, 7 tables, 16 figures, accepted by MNRA
Hunting for the progenitor of SN 1006: High resolution spectroscopic search with the FLAMES instrument
Type Ia supernovae play a significant role in the evolution of the Universe
and have a wide range of applications. It is widely believed that these events
are the thermonuclear explosions of carbon-oxygen white dwarfs close to the
Chandrasekhar mass (1.38 M\odot). However, CO white dwarfs are born with masses
much below the Chandrasekhar limit and thus require mass accretion to become
Type Ia supernovae. There are two main scenarios for accretion. First, the
merger of two white dwarfs and, second, a stable mass accretion from a
companion star. According to predictions, this companion star (also referred to
as donor star) survives the explosion and thus should be visible in the center
of Type Ia remnants. In this paper we scrutinize the central stars (79 in
total) of the SN 1006 remnant to search for the surviving donor star as
predicted by this scenario. We find no star consistent with the traditional
accretion scenario in SN1006.Comment: 11 pages, accepted by Ap
Dalek -- a deep-learning emulator for TARDIS
Supernova spectral time series contain a wealth of information about the
progenitor and explosion process of these energetic events. The modeling of
these data requires the exploration of very high dimensional posterior
probabilities with expensive radiative transfer codes. Even modest
parametrizations of supernovae contain more than ten parameters and a detailed
exploration demands at least several million function evaluations. Physically
realistic models require at least tens of CPU minutes per evaluation putting a
detailed reconstruction of the explosion out of reach of traditional
methodology. The advent of widely available libraries for the training of
neural networks combined with their ability to approximate almost arbitrary
functions with high precision allows for a new approach to this problem.
Instead of evaluating the radiative transfer model itself, one can build a
neural network proxy trained on the simulations but evaluating orders of
magnitude faster. Such a framework is called an emulator or surrogate model. In
this work, we present an emulator for the TARDIS supernova radiative transfer
code applied to Type Ia supernova spectra. We show that we can train an
emulator for this problem given a modest training set of a hundred thousand
spectra (easily calculable on modern supercomputers). The results show an
accuracy on the percent level (that are dominated by the Monte Carlo nature of
TARDIS and not the emulator) with a speedup of several orders of magnitude.
This method has a much broader set of applications and is not limited to the
presented problem.Comment: 6 pages;5 figures submitted to AAS Journals. Constructive Criticism
invite
A High-Resolution Spectroscopic Search for the Remaining Donor for Tycho's Supernova
In this paper, we report on our analysis using Hubble Space Telescope
astrometry and Keck-I HIRES spectroscopy of the central six stars of Tycho's
supernova remnant (SN 1572). With these data, we measured the proper motions,
radial velocities, rotational velocities, and chemical abundances of these
objects. Regarding the chemical abundances, we do not confirm the unusu- ally
high [Ni/Fe] ratio previously reported for Tycho-G. Rather, we find that for
all metrics in all stars, none exhibit the characteristics expected from
traditional SN Ia single-degenerate-scenario calculations. The only possible
exception is Tycho-B, a rare, metal-poor A-type star; however, we are unable to
find a suitable scenario for it. Thus, we suggest that SN 1572 cannot be
explained by the standard single-degenerate model.Comment: 34 pages, 11 Figures, revised and resubmitted to Ap