103 research outputs found
The Outcome of Supernovae in Massive Binaries; Removed Mass, and its Separation Dependence
The majority of massive stars are formed in binary systems. It is hence
reasonable to expect that most core-collapse supernovae (CCSNe) take place in
binaries and the existence of a companion star may leave some imprints in
observed features. Having this in mind, we have conducted two-dimensional
hydrodynamical simulations of the collisions of CCSNe ejecta with the companion
star in an almost-equal-mass () binary to find out possible
consequences of such events. In particular we pay attention to the amount of
mass removed and its dependence on the binary separation. In contrast to the
previous surmise, we find that the companion mass is stripped not by momentum
transfer but by shock heating. Up to of the original mass can be removed
for the closest separations and the removed mass decreases as with the binary separation . By performing some experimental
computations with artificially-modified densities of incident ejecta, we show
that if the velocity of ejecta is fixed, the density of incident ejecta is the
single important parameter that actually determines the removed mass as . On the other hand, another set of simulations with
modified velocities of incident ejecta demonstrate that the strength of the
forward shock, which heats up the stellar material and causes the mass loss of
the companion star, is actually the key parameter for the removed mass.Comment: 16 pages, accepted for publication in the Astrophysical Journa
Constraining mass transfer and common-envelope physics with post-supernova companion monitoring
We present an analytical model that describes the response of companion stars
after being impacted by a supernova in a close binary system. This model
captures key properties of the luminosity evolution obtained from 1D stellar
evolution calculations fairly well: a high-luminosity plateau phase and a
decaying tail phase. It can be used to constrain the pre-supernova binary
properties from the observed photometry of the companion star several years
after the explosion in a relatively simple manner. The derived binary
parameters are useful in constraining the evolutionary scenario for the
progenitors and the physics of binary interactions. We apply our model to some
known stripped-envelope supernova companions (SN1993J, SN2001ig, SN2006jc,
SN2011dh, SN2013ge). Combined with other observational constraints such as the
pre-supernova progenitor photometry, we find that SN1993J and SN2011dh likely
had relatively massive companions on wide orbits, while SN2006jc may have had a
relatively low-mass companion on a tight orbit. This trend suggests that type
IIb supernova progenitors evolved from stable mass transfer channels and type
Ibc progenitors may have formed from common-envelope channels. The constraints
on orbital separation helps us probe the highly uncertain common-envelope
physics for massive stars, especially with multiple epochs of companion
observations. We also highlight possible limitations of our model due to the
assumptions made in the underlying 1D models.Comment: 9 pages, 9 figures. Accepted for publication in MNRA
Comprehensive study of ejecta-companion interaction for core-collapse supernovae in massive binaries
We carry out a comprehensive study of supernova ejecta-companion interaction
in massive binary systems. We aim to physically understand the kinematics of
the interaction and predict observational signatures. To do this we perform
simulations over a vast parameter space of binary configurations, varying the
masses of the progenitor and companion, structure of the companion, explosion
energy, and orbital separation. Our results were not so consistent with
classical models by Wheeler et al. 1975, sometimes deviating by an order of
magnitude. We construct an alternative simple model which explains the
simulated results reasonably well and can be used to estimate impact velocities
for arbitrary explosion profiles and companion star structures. We then
investigate the long term evolution after the supernova, where the companion
can be inflated by the energy injected into the star. We find that the
companion can become more than an order of magnitude overluminous straight
after the supernova, but quickly fades away after years and returns to
its original luminosity in about a thermal timescale of the star. Finally, we
also discuss the possible surface contamination of heavy elements from the
slower ejecta.Comment: 24 pages, 21 figures, accepted by the Astrophysical Journa
Polyhedral Clinching Auctions for Indivisible Goods
In this study, we propose polyhedral clinching auctions for indivisible
goods, which has so far been studied for divisible goods. As in the divisible
setting by Goel et al., our mechanism enjoys incentive compatibility,
individual rationality, and Pareto optimality, and works with polymatroidal
environments. A notable feature for the indivisible setting is that the whole
procedure can be conducted in time polynomial of the number of buyers and
goods. Moreover, we show additional efficiency guarantees, recently established
by Sato for the divisible setting, that the liquid welfare (LW) of our
mechanism achieves more than 1/2 of the optimal LW, and that the social welfare
is more than the optimal LW
Neutron stars colliding with binary companions: formation of hypervelocity stars, pulsar planets, bumpy superluminous supernovae and Thorne-\.Zytkow objects
We perform 3D hydrodynamical simulations of new-born neutron stars (NSs)
colliding with main-sequence binary companions after supernova explosions.
Based on those hydrodynamical models, we construct a semi-analytical formula
that describes the drag force inside stars with steep density gradients. We
then compute the outcome of NS--companion collisions over a wide range of
parameters using the semi-analytical formula. Depending on the direction and
magnitude of the natal kick, we find that the collision may lead to various
outcomes. For relatively fast kicks and high impact parameters, the NS may
penetrate the companion star envelope without merging. By allowing the NS to
plunge through companions, the companion can be accelerated to have runaway
velocities up to per cent above the theoretical upper limit considered
in classical binary disruption scenarios. The NS can capture and carry away up
to a few per cent of the companion envelope as it escapes, which may form
pulsar planets or cause outflows through accretion to heat the ejecta from
inside and power the supernova light curve. For lower impact parameters, the
neutron star will directly merge with the companion and form a Thorne-\.Zytkow
object. In intermediate cases, the NS penetrates the companion envelope several
times before merging, possibly causing multiple bumps in the supernova light
curve like in SN2015bn and SN2019stc.Comment: 13 pages, 13 figures, comments welcom
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