38 research outputs found
Missing Red Supergiants and Carbon Burning
Recent studies on direct imaging of Type II core-collapse supernova
progenitors indicate a possible threshold around
M, where red supergiants with larger birth masses do not appear to
result in supernova explosions and instead implode directly into a black hole.
In this study we argue that it is not a coincidence that this threshold closely
matches the critical transition of central Carbon burning in massive stars from
the convective to radiative regime. In lighter stars, Carbon burns convectively
in the center and result in compact final presupernova cores that are likely to
result in explosions, while in heavier stars after the transition, it burns as
a radiative flame and the stellar cores become significantly harder to explode.
Using the KEPLER code we demonstrate the sensitivity of this transition to the
rate of CO reaction and the overshoot mixing
efficiency, and we argue that the upper mass limit of exploding red supergiants
could be employed to constrain uncertain input physics of massive stellar
evolution calculations. The initial mass corresponding to the central Carbon
burning transition range from 14 to 26 M in recently published models
from various groups and codes, and only a few are in agreement with the
estimates inferred from direct imaging studies.Comment: submitted to MNRA
Confronting Models of Massive Star Evolution and Explosions with Remnant Mass Measurements
The mass distribution of compact objects provides a fossil record that can be
studied to uncover information on the late stages of massive star evolution,
the supernova explosion mechanism, and the dense matter equation of state.
Observations of neutron star masses indicate a bimodal Gaussian distribution,
while the observed black hole mass distribution decays exponentially for
stellar-mass black holes. We use these observed distributions to directly
confront the predictions of stellar evolution models and the neutrino-driven
supernova simulations of Sukhbold et al. (2016). We find excellent agreement
between the black hole and low-mass neutron star distributions created by these
simulations and the observations. We show that a large fraction of the stellar
envelope must be ejected, either during the formation of stellar-mass black
holes or prior to the implosion through tidal stripping due to a binary
companion, in order to reproduce the observed black hole mass distribution. We
also determine the origins of the bimodal peaks of the neutron star mass
distribution, finding that the low-mass peak (centered at ~1.4 M_sun)
originates from progenitors with M_zams ~ 9-18 M_sun. The simulations fail to
reproduce the observed peak of high-mass neutron stars (centered at ~1.8 M_sun)
and we explore several possible explanations. We argue that the close agreement
between the observed and predicted black hole and low-mass neutron star mass
distributions provides new promising evidence that these stellar evolution and
explosion models are accurately capturing the relevant stellar, nuclear, and
explosion physics involved in the formation of compact objects.Comment: Typos in fit coefficients corrected, results unchanged. 13 pages, 10
figures. Submitted to Ap
Missing red supergiants and carbon burning
Recent studies on direct imaging of Type II core-collapse supernova progenitors indicate a possible threshold around M_(ZAMS) ∼ 16–20 M⊙, where red supergiants (RSG) with larger birth masses do not appear to result in supernova explosions and instead implode directly into a black hole. In this study, we argue that it is not a coincidence that this threshold closely matches the critical transition of central carbon burning in massive stars from the convective to radiative regime. In lighter stars, carbon burns convectively in the centre and result in compact final pre-supernova cores that are likely to result in explosions, while in heavier stars after the transition, it burns as a radiative flame and the stellar cores become significantly harder to explode. Using the keplerkepler code we demonstrate the sensitivity of this transition to the rate of ¹²C(α, γ)¹⁶O reaction and the overshoot mixing efficiency, and we argue that the upper mass limit of exploding RSG could be employed to constrain uncertain input physics of massive stellar evolution calculations. The initial mass corresponding to the central carbon burning transition range from 14 to 26 M⊙ in recently published models from various groups and codes, and only a few are in agreement with the estimates inferred from direct imaging studies
Periodic Variables in the Open Cluster NGC 2301
We present the results of a search for periodic variables within 4078
time-series light curves and an analysis of the period-color plane for stars in
the field of the open cluster NGC2301. One hundred thirty-eight periodic
variables were discovered, of which five are eclipsing binary candidates with
unequal minima. The remaining 133 periodic variables appear to consist mainly
of late-type stars whose variation is due to rotation modulated by star spot
activity. The determined periods range from less than a day to over 14 days and
have nearly unreddened B-R colors in the range of 0.8 to 2.8. The Barnes (2003)
interpretation of the period-color plane of late type stars is tested with our
data. Our data did not show distinct I and C sequences, likely due to nonmember
field stars contaminating in the background, as we estimate the total
contamination to be 43%. Using different assumptions, the gyrochronological age
of the cluster is calculated to be 210+/-25 Myr, which falls in the range of
age values (164-250 Myr) determined by previous studies. Finally, we present
evidence which nullifies the earlier suggestion that two of the variable stars
in NGC2301 might be white dwarfs.Comment: 17pages, 12 figures, 3 table