13 research outputs found
Related progenitor models for long-duration gamma ray bursts and Type Ic superluminous supernovae
We model the late evolution and mass loss history of rapidly rotating
Wolf-Rayet stars in the mass range . We find that quasi-chemically homogeneously evolving
single stars computed with enhanced mixing retain very little or no helium and
are compatible with Type\,Ic supernovae. The more efficient removal of core
angular momentum and the expected smaller compact object mass in our lower mass
models lead to core spins in the range suggested for magnetar driven
superluminous supernovae. Our more massive models retain larger specific core
angular momenta, expected for long-duration gamma-ray bursts in the collapsar
scenario. Due to the absence of a significant He envelope, the rapidly
increasing neutrino emission after core helium exhaustion leads to an
accelerated contraction of the whole star, inducing a strong spin-up, and
centrifugally driven mass loss at rates of up to
in the last years to decades before core
collapse. Since the angular momentum transport in our lower mass models
enhances the envelope spin-up, they show the largest relative amounts of
centrifugally enforced mass loss, i.e., up to 25\% of the expected ejecta mass.
Our most massive models evolve into the pulsational pair-instability regime. We
would thus expect signatures of interaction with a C/O-rich circumstellar
medium for Type~Ic superluminous supernovae with ejecta masses below and for the most massive engine-driven explosions with
ejecta masses above . Signs of such interaction should
be observable at early epochs of the supernova explosion, and may be related to
bumps observed in the light curves of superluminous supernovae, or to the
massive circumstellar CO-shell proposed for Type~Ic superluminous supernova
Gaia16apd.Comment: 20 pages, 15 figures, 2 tables Accepted for publication in Ap
The origin of pulsating ultra-luminous X-ray sources: Low- and intermediate-mass X-ray binaries containing neutron star accretors
Ultra-luminous X-ray sources (ULXs) are those X-ray sources located away from
the centre of their host galaxy with luminosities exceeding the Eddington limit
of a stellar-mass black hole (). The discovery
of X-ray pulsations in some of these objects (e.g. M82~X-2) suggests that a
certain fraction of the ULX population may have a neutron star accretor. We
present systematic modelling of low- and intermediate-mass X-ray binaries
(LMXBs and IMXBs; donor-star mass range --~M and
neutron-star accretors) to explain the formation of this sub-population of
ULXs. Using MESA, we explored the allowed initial parameter space of binary
systems consisting of a neutron star and a low- or intermediate-mass donor star
that could explain the observed properties of ULXs. Our simulations take into
account beaming effects, stellar rotation, general angular momentum losses, and
a detailed and self-consistent calculation of the mass-transfer rate. We study
the conditions that lead to dynamical stability of these systems, which depends
strongly on the response of the donor star to mass loss. Using two values for
the initial neutron star mass (~M and ~M), we
present two sets of mass-transfer calculation grids. We find that LMXBs/IMXBs
can produce NS-ULXs with typical time-averaged isotropic-equivalent X-ray
luminosities of -- on a timescale up to
for the lower luminosities. We also estimate their
likelihood of detection, the types of white-dwarf remnants left behind by the
donors, and the total amount of mass accreted by the neutron stars. We also
compare our results to the observed pulsating ULXs. Our results suggest that a
large subset of the observed pulsating ULX population can be explained by
LMXBs/IMXBs undergoing a super-Eddington mass-transfer phase.Comment: 19 pages, 13 figures, Accepted by A&A. Parameter space was increased
to include low-mass XRBs and corresponding changes made to the text
(including the title) and figures 4, 6-11. Changed axes for figures 1 and 2.
Fixed typos and updated references. Added arguments about why spin period is
not an accurate reflection of mass accretion rate in the introductio
Density Profiles of Collapsed Rotating Massive Stars Favor Long Gamma-Ray Bursts
Long-duration gamma-ray bursts (lGRBs) originate in relativistic collimated
outflows -- jets -- that drill their way out of collapsing massive stars.
Accurately modeling this process requires realistic stellar profiles for the
jets to propagate through and break out of. Most previous studies have used
simple power laws or pre-collapse models for massive stars. However, the
relevant stellar profile for lGRB models is in fact that of a star after its
core has collapsed to form a compact object. To self-consistently compute such
a stellar profile, we use the open-source code GR1D to simulate the
core-collapse process for a suite of low-metallicity, rotating, massive stellar
progenitors that have undergone chemically homogeneous evolution. Our models
span a range of zero-age main sequence (ZAMS) masses: , and . All of these models, at the onset of
core-collapse, feature steep density profiles, with
, which would result in jets that are inconsistent with lGRB
observables. We follow the collapse of four out of our seven models until they
form BHs and the other three proto-neutron stars (PNSs). We find, across all
models, that the density profile outside of the newly-formed BH or PNS is
well-represented by a flatter power law with . Such
flat density profiles are conducive to successful formation and breakout of
BH-powered jets and, in fact, required to reproduce observable properties of
lGRBs. Future models of lGRBs should be initialized with shallower
\textit{post-collapse} stellar profiles like those presented here instead of
the much steeper pre-collapse profiles that are typically used.Comment: 9 pages, 4 figures+1 table, submitted to ApJL, comments welcom
A three-dimensional hydrodynamics simulation of oxygen-shell burning in the final evolution of a fast-rotating massive star
We perform for the first time a 3D hydrodynamics simulation of the evolution
of the last minutes pre-collapse of the oxygen shell of a fast-rotating massive
star. This star has an initial mass of 38 M, a metallicity of
1/50 Z, an initial rotational velocity of 600 km s, and
experiences chemically homogeneous evolution. It has a silicon- and oxygen-rich
(Si/O) convective layer at (4.7-17) cm, where oxygen-shell
burning takes place. The power spectrum analysis of the turbulent velocity
indicates the dominance of the large-scale mode (), which has also
been seen in non-rotating stars that have a wide Si/O layer. Spiral arm
structures of density and silicon-enriched material produced by oxygen-shell
burning appear in the equatorial plane of the Si/O shell. Non-axisymmetric,
large-scale () modes are dominant in these structures. The spiral arm
structures have not been identified in previous non-rotating 3D pre-supernova
models. Governed by such a convection pattern, the angle-averaged specific
angular momentum becomes constant in the Si/O convective layer, which is not
considered in spherically symmetrical stellar evolution models. Such spiral
arms and constant specific angular momentum might affect the ensuing explosion
or implosion of the star.Comment: 6 pages, 6 figures, accepted for publication in MNRAS Letter
Supernovae Ib and Ic from the explosion of helium stars
Much difficulty has so far prevented the emergence of a consistent scenario for the origin of Type Ib and Ic supernovae (SNe). Here, we follow a heuristic approach by examining the fate of helium stars in the mass range 4 to 12Msun, which presumably form in interacting binaries. The helium stars are evolved using stellar wind mass loss rates that agree with observations, and which reproduce the observed luminosity range of galactic WR stars, leading to stellar masses at core collapse in the range 3-5.5Msun. We then explode these models adopting an explosion energy proportional to the ejecta mass, roughly consistent with theoretical predictions. We impose a fixed 56Ni mass and strong mixing. The SN radiation from 3 to 100d is computed self-consistently starting from the input stellar models using the time-dependent non-local thermodynamic equilibrium radiative-transfer code CMFGEN. By design, our fiducial models yield similar light curves, with a rise time of ~20d and a peak luminosity of ~10^42.2erg/s, in line with representative SNe Ibc. The less massive progenitors retain a He-rich envelope and reproduce the color, line widths, and line strengths of a representative sample of SNe Ib, while stellar winds remove most of the helium in more massive progenitors, whose spectra match typical SNe Ic in detail. The transition between the predicted Ib-like and Ic-like spectra is continuous, but it is sharp, such that the resulting models essentially form a dichotomy. Further models computed with varying explosion energy, 56Ni mass, and long-term power injection from the remnant show that a moderate variation of these parameters can reproduce much of the diversity of SNe Ibc. We conclude that stars stripped by a binary companion can account for the vast majority of ordinary SNe Ib and Ic, and that stellar wind mass loss is the key to remove the helium envelope in SN Ic progenitors. [abridged
Thermonuclear and Electron-Capture Supernovae from Stripped-Envelope Stars
(abridged) When stripped from their hydrogen-rich envelopes, stars with
initial masses between 7 and 11 M develop massive degenerate
cores and collapse. Depending on the final structure and composition, the
outcome can range from a thermonuclear explosion, to the formation of a neutron
star in an electron-capture supernova (ECSN). It has been recently demonstrated
that stars in this mass range may initiate explosive oxygen burning when their
central densities are still below g cm.
This makes them interesting candidates for Type Ia Supernovae -- which we call
(C)ONe SNe Ia -- and might have broader implications for the formation of
neutron stars via ECSNe. Here, we model the evolution of 252 helium-stars with
initial masses in the M range, and metallicities between
and . We use these models to constrain the central densities,
compositions and envelope masses at the time of explosive oxygen ignition. We
further investigate the sensitivity of these properties to mass-loss rate
assumptions using additional models with varying wind efficiencies. We find
that helium-stars with masses between 1.8 and 2.7 M evolve onto
M (C)ONe cores that initiate explosive burning at central
densities between and 9.6. We constrain the
amount of residual carbon retained after core carbon burning, and conclude that
it plays a critical role in determining the final outcome: Cores with residual
carbon mass fractions of result in
(C)ONe SNe Ia, while those with lower carbon mass fractions become ECSNe. We
find that (C)ONe SNe Ia are more likely to occur at high metallicities, whereas
at low metallicities ECSNe dominate.Comment: Submitted to Astronomy & Astrophysics; comments are welcom
Stripped-envelope stars in different metallicity environments. II. Type I supernovae and compact remnants
Stripped-envelope stars can be observed as Wolf-Rayet (WR) stars, or as less luminous hydrogen-poor stars with low mass loss rates and transparent winds. Both types are potential progenitors of Type I core-collapse supernovae (SNe). We use grids of core-collapse models obtained from helium stars at different metallicities to study the effects of metallicity on the transients and remnants these stars produce. We characterise the surface and core properties of our core collapse models, and investigate their explodability employing three criteria. In cases where explosions are predicted, we estimate the ejecta mass, explosion energy, nickel mass and neutron star (NS) mass. Otherwise, we predict the mass of the resulting black hole (BH). We construct a simplified population model, and find that the properties SNe and compact objects depend strongly on metallicity. Ejecta masses and explosion energies for Type Ic SNe are best reproduced by models with Z=0.04 which exhibit strong winds during core helium burning. This implies that either their mass loss rates are underestimated, or that Type Ic SN progenitors experience mass loss through other mechanisms before exploding. The distributions of ejecta masses, explosion energies and nickel mass for Type Ib SNe are not well reproduced by progenitor models with WR mass loss, but are better reproduced if we assume no mass loss in progenitors with luminosities below the minimum WR star luminosity. We find that Type Ic SNe become more common as metallicity increases, and that the vast majority of progenitors of Type Ib SNe must be transparent-wind stripped-envelope stars. We find several models with pre-collapse CO-masses of up to may form BHs in fallback SNe. This may carry important consequences for our understanding of SNe, binary BH and NS systems, X-ray binary systems and gravitational wave transients
Three-dimensional hydrodynamics simulations of shell burning in Si/O-rich layer of pre-collapse massive stars
We perform three-dimensional (3D)hydrodynamics simulations of shell burning in the silicon-and oxygen-rich layers in pre-collapse massive stars.Weadoptanon-rotating27 M⊙ starhaving anextended O/Si/Ne layer and afast-rotating 38 M⊙ star having a Si/Olayer, that has experienced chemically homogeneousevolution. Both pre-collapse stars showlarge-scale turbulent motion with a maximum Mach number of ~0.1 in the convective layers activated byneonand oxygenshellburning.The radialproflieoftheangle-averaged mass fraction distributioninO/Si/Ne layer is more homogeneous in the 3D simulation compared to the 1D evolution for the 27 M⊙ star. The angle-averaged specific angular momentum in the Si/O layer of the fast-rotating 38 M⊙ star tends to become roughly constant in the convective layer of the 3D simulation, which is not considered in the 1D evolution
Stripped-envelope stars in different metallicity environments. II. Type I supernovae and compact remnants
Stripped-envelope stars can be observed as Wolf-Rayet (WR) stars, or as less
luminous hydrogen-poor stars with low mass loss rates and transparent winds.
Both types are potential progenitors of Type I core-collapse supernovae (SNe).
We use grids of core-collapse models obtained from helium stars at different
metallicities to study the effects of metallicity on the transients and
remnants these stars produce. We characterise the surface and core properties
of our core collapse models, and investigate their explodability employing
three criteria. In cases where explosions are predicted, we estimate the ejecta
mass, explosion energy, nickel mass and neutron star (NS) mass. Otherwise, we
predict the mass of the resulting black hole (BH). We construct a simplified
population model, and find that the properties SNe and compact objects depend
strongly on metallicity. Ejecta masses and explosion energies for Type Ic SNe
are best reproduced by models with Z=0.04 which exhibit strong winds during
core helium burning. This implies that either their mass loss rates are
underestimated, or that Type Ic SN progenitors experience mass loss through
other mechanisms before exploding. The distributions of ejecta masses,
explosion energies and nickel mass for Type Ib SNe are not well reproduced by
progenitor models with WR mass loss, but are better reproduced if we assume no
mass loss in progenitors with luminosities below the minimum WR star
luminosity. We find that Type Ic SNe become more common as metallicity
increases, and that the vast majority of progenitors of Type Ib SNe must be
transparent-wind stripped-envelope stars. We find several models with
pre-collapse CO-masses of up to may form
BHs in fallback SNe. This may carry important consequences for our
understanding of SNe, binary BH and NS systems, X-ray binary systems and
gravitational wave transients.Comment: 30 pages, 20 figures, submitted to Astronomy & Astrophysic