9,699 research outputs found
Mass loss of massive stars near the Eddington luminosity by core neutrino emission shortly before their explosion
We present a novel mechanism to enhance the mass-loss rates of massive stars
shortly before their explosion. The neutrino luminosities of the stellar core
of massive stars become larger as they get closer to the time of the core
collapse. As emitted neutrinos escape freely from the core, the core mass is
significantly reduced when the neutrino luminosity is large. If a star is near
the Eddington luminosity when the neutrino luminosity is large, the star can
exceed the Eddington luminosity because of the core neutrino mass loss. We
suggest that the stellar surface mass-loss rates due to the core neutrino
emission can be higher than 1e-4 Msun/yr from ~ 1 year before the core
collapse. The mass-loss rates can exceed 1e-2 Msun/yr in ~ 10 days before the
core collapse. This mass-loss mechanism may be able to explain the enhanced
mass loss observed in some supernova progenitors shortly before their
explosion. Even if the star is not close enough to the Eddington luminosity to
enhance mass loss, the star can still expand because of the reduced
gravitational force. This mechanism can be activated in Wolf-Rayet stars and it
can make hydrogen-poor, as well as hydrogen-rich, dense circumstellar media
observed in some supernovae.Comment: 5 pages, 2 figures, accepted by Astronomy & Astrophysic
Pulsations of red supergiant pair-instability supernova progenitors leading to extreme mass loss
Recent stellar evolution models show consistently that very massive
metal-free stars evolve into red supergiants shortly before they explode. We
argue that the envelopes of these stars, which will form pair-instability
supernovae, become pulsationally unstable and that this will lead to extreme
mass-loss rates despite the tiny metal content of the envelopes. We investigate
the pulsational properties of such models and derive pulsationally induced
mass-loss rates, which take the damping effects of the mass loss on the
pulsations selfconsistently into account. We find that the pulsations may
induce mass-loss rates of ~ 1e-4 - 1e-2 Msun/yr shortly before the explosions,
which may create a dense circumstellar medium. Our results show that very
massive stars with dense circumstellar media may stem from a wider initial mass
range than pulsational-pair instability supernovae. The extreme mass loss will
cease when so much of the hydrogen-rich envelope is lost that the star becomes
more compact and stops pulsating. The helium core of these stars therefore
remains unaffected, and their fate as pair-instability supernovae remains
unaltered. The existence of dense circumstellar media around metal-free
pair-instability supernovae can make them brighter and bluer, and they may be
easier to detect at high redshifts than previously expected. We argue that the
mass-loss enhancement in pair-instability supernova progenitors can naturally
explain some observational properties of superluminous supernovae: the
energetic explosions of stars within hydrogen-rich dense circumstellar media
with little 56Ni production and the lack of a hydrogen-rich envelope in
pair-instability supernova candidates with large 56Ni production.Comment: 11 pages, 10 figures, 1 table, accepted by Astronomy & Astrophysics,
proofed in v
Systematic investigation of the fallback accretion powered model for hydrogen-poor superluminous supernovae
The energy liberated by fallback accretion has been suggested as a possible
engine to power hydrogen-poor superluminous supernovae. We systematically
investigate this model using the Bayesian light-curve fitting code MOSFiT
(Modular Open Source Fitter for Transients), fitting the light curves of 37
hydrogen-poor superluminous supernovae assuming a fallback accretion central
engine. We find that this model can yield good fits to their light curves, with
a fit quality that rivals the popular magnetar engine models. Examining our
derived parameters for the fallback model, we find the total energy
requirements from the accretion disk are estimated to be 0.002 - 0.7 Msun c^2.
If we adopt a typical conversion efficiency ~ 1e-3, the required mass to
accrete is thus 2 - 700 Msun. Many superluminous supernovae, therefore, require
an unrealistic accretion mass, and so only a fraction of these events could be
powered by fallback accretion unless the true efficiency is much greater than
our fiducial value. The superluminous supernovae that require the smallest
amounts of fallback mass still remain to be the fallback accretion powered
supernova candidates, but they are difficult to be distinguished solely by
their light curve properties.Comment: 12 pages, 8 figures, 3 tables, accepted by The Astrophysical Journa
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