394 research outputs found
The Metallicity Dependence of the Minimum Mass for Core-Collapse Supernovae
Understanding the progenitors of core collapse supernovae and their
population statistics is a key ingredient for many current studies in astronomy
but as yet this remains elusive. Using the MESA stellar evolution code we study
the dependence of the lower mass limit for making core collapse supernovae
(SNe) as function of initial stellar metallicity. We find that this mass limit
is smallest at approximately [Z] = -2 with a value of ~ 8.3 Msun. At [Z] = 0
the limit is ~ 9.5 Msun and continues to rise with higher metallicity. As a
consequence, for a fixed initial mass function the supernova rate may be 20% to
25% higher at [Z] = -2. This affects the association of observed SN rates as a
probe for the cosmological star formation rate, rate predictions for supernova
surveys, and population synthesis studies.Comment: 13 pages, 1 figure, 1 table, submitted to ApJ
Combined Nucleosynthetic Yields of Multiple First Stars
Modern numerical simulations of the formation of the first stars predict that
the first stars formed in multiples. In those cases, the chemical yields of
multiple supernova explosions may have contributed to the formation of a next
generation star. We match the chemical abundances of the oldest observed stars
in the universe to a database of theoretical supernova models, to show that it
is likely that the first stars formed from the ashes of two or more
progenitors.Comment: 3 pages, 2 figures, NIC 2016 Conference Proceeding
The quest for blue supergiants: binary merger models for the evolution of the progenitor of SN 1987A
We present the results of a detailed, systematic stellar evolution study of
binary mergers for blue supergiant (BSG) progenitors of Type II supernovae. In
particular, these are the first evolutionary models that can simultaneously
reproduce nearly all observational aspects of the progenitor of SN 1987A,
\text{Sk}-69\,^{\circ}202, such as its position in the HR diagram, the
enrichment of helium and nitrogen in the triple-ring nebula, and its lifetime
before its explosion. The merger model, based on the one proposed by
Podsiadlowski 1992 et al. and Podsiadlowski 2007 et al., consists of a main
sequence secondary star that dissolves completely in the common envelope of the
primary red supergiant at the end of their merger. We empirically explore a
large initial parameter space, such as primary masses (,
, and ), secondary masses
(, , ..., ) and
different depths up to which the secondary penetrates the He core of the
primary during the merger. The evolution of the merged star is continued until
just before iron-core collapse and the surface properties of the 84
pre-supernova models () computed
have been made available in this work. Within the parameter space studied, the
majority of the pre-supernova models are compact, hot BSGs with effective
temperature and radii of
of which six match nearly all the
observational properties of \text{Sk}-69\,^{\circ}202.Comment: Submitted to MNRAS. 21 pages, 11 figures, 7 table
Long Gamma-Ray Transients from Collapsars
In the collapsar model for common gamma-ray bursts, the formation of a
centrifugally supported disk occurs during the first 10 seconds following
the collapse of the iron core in a massive star. This only occurs in a small
fraction of massive stellar deaths, however, and requires unusual conditions. A
much more frequent occurrence could be the death of a star that makes a black
hole and a weak or absent outgoing shock, but in a progenitor that only has
enough angular momentum in its outermost layers to make a disk. We consider
several cases where this is likely to occur - blue supergiants with low mass
loss rates, tidally-interacting binaries involving either helium stars or giant
stars, and the collapse to a black hole of very massive pair-instability
supernovae. These events have in common the accretion of a solar mass or so of
material through a disk over a period much longer than the duration of a common
gamma-ray burst. A broad range of powers is possible, to
erg s, and this brightness could be enhanced by beaming. Such
events were probably more frequent in the early universe where mass loss rates
were lower. Indeed this could be one of the most common forms of gamma-ray
transients in the universe and could be used to study first generation stars.
Several events could be active in the sky at any one time. A recent example of
this sort of event may have been the SWIFT transient Sw-1644+57.Comment: submitted to Astrophysical Journa
Reducing Uncertainties in the Production of the Gamma Emitting Nuclei 26Al, 44Ti, and 60Fe in Core Collapse Supernovae by Using Effective Helium Burning Rates
We have used effective reaction rates (ERR) for the helium burning reactions
to predict the yield of the gamma-emitting nuclei 26Al, 44Ti, and 60Fe in core
col- lapse supernovae. The variations in the predicted yields for values of the
reaction rates allowed by the ERR are much smaller than obtained previously,
and smaller than other uncertainties. A "filter" for supernova nucleosynthesis
yields based on pre-supernova structure was used to estimate the effect of
failed supernovae on the initial mass function-averaged yields; this
substantially reduced the yields of all these isotopes, but the predicted yield
ratio 60Fe/26Al was little affected. The robustness of this ratio is promising
for comparison with data, but it is larger than observed in nature; possible
causes for this discrepancy are discussed.Comment: 16 pages, 3 figure
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