25 research outputs found
Progenitors of supernova Ibc: a single Wolf-Rayet star as the possible progenitor of the SN Ib iPTF13bvn
Core-collapse supernova (SN) explosions mark the end of the tumultuous life
of massive stars. Determining the nature of their progenitors is a crucial step
towards understanding the properties of SNe. Until recently, no progenitor has
been directly detected for SN of type Ibc, which are believed to come from
massive stars that lose their hydrogen envelope through stellar winds and from
binary systems where the companion has stripped the H envelope from the
primary. Here we analyze recently reported observations of iPTF13bvn, which
could possibly be the first detection of a SN Ib progenitor based on
pre-explosion images. Very interestingly, the recently published Geneva models
of single stars can reproduce the observed photometry of the progenitor
candidate and its mass-loss rate, confirming a recently proposed scenario. We
find that a single WR star with initial mass in the range 31-35 Msun fits the
observed photometry of the progenitor of iPTF13bvn. The progenitor likely has a
luminosity of log (L/Lsun)~5.55, surface temperature ~45000 K, and mass of
~10.9 Msun at the time of explosion. Our non-rotating 32 Msun model
overestimates the derived radius of the progenitor, although this could likely
be reconciled with a fine-tuned model of a more massive (between 40 and 50
Msun), hotter, and luminous progenitor. Our models indicate a very uncertain
ejecta mass of ~8 Msun, which is higher than the average of the SN Ib ejecta
mass that is derived from the lightcurve (2-4 Msun). This possibly high ejecta
mass could produce detectable effects in the iPTF13bvn lightcurve and spectrum.
If the candidate is indeed confirmed to be the progenitor, our results suggest
that stars with relatively high initial masses (>30 Msun) can produce visible
SN explosions at their deaths and do not collapse directly to a black hole.Comment: 4 pages, 2 figures, accepted for publication in A&
Can massive Be/Oe stars be progenitors of long gamma ray bursts?
Context: The identification of long-gamma-ray-bursts (LGRBs) is still
uncertain, although the collapsar engine of fast-rotating massive stars is
gaining a strong consensus. Aims: We propose that low-metallicity Be and Oe
stars, which are massive fast rotators, as potential LGRBs progenitors.
Methods: We checked this hypothesis by 1) testing the global specific angular
momentum of Oe/Be stars in the ZAMS with the SMC metallicity, 2) comparing the
ZAMS () parameters of these stars with the
area predicted theoretically for progenitors with metallicity , and 3)
calculating the expected rate of LGRBs/year/galaxy and comparing them with the
observed ones. To this end, we determined the ZAMS linear and angular
rotational velocities for SMC Be and Oe stars using the observed vsini
parameters, corrected from the underestimation induced by the gravitational
darkening effect. Results: The angular velocities of SMC Oe/Be stars are on
average in the ZAMS. These velocities are in the
area theoretically predicted for the LGRBs progenitors. We estimated the yearly
rate per galaxy of LGRBs and the number of LGRBs produced in the local Universe
up to z=0.2. We have considered that the mass range of LGRB progenitors
corresponds to stars hotter than spectral types B0-B1 and used individual
beaming angles from 5 to 15\degr. We thus obtain to LGRBs/year/galaxy, which represents on
average 2 to 14 LGRB predicted events in the local Universe during the past 11
years. The predicted rates could widely surpass the observed ones
[(0.2-3) LGRBs/year/galaxy; 8 LGRBs observed in the local
Universe during the last 11 years] if the stellar counts were made from the
spectral type B1-B2, in accordance with the expected apparent spectral types of
the appropriate massive fast rotators. Conclusion: We conclude that the massive
Be/Oe stars with SMC metallicity could be LGRBs progenitors. Nevertheless,
other SMC O/B stars without emission lines, which have high enough specific
angular momentum, can enhance the predicted rate
The past and future evolution of a star like Betelgeuse
We discuss the physics and the evolution of a typical massive star passing
through an evolutionary stage similar to that of Betelgeuse. After a brief
introduction recalling various observed parameters of Betelgeuse, we discuss
the Pre-Main-Sequence phase (PMS), the Main-Sequence (MS) phase, the physics
governing the duration of the first crossing of the HR diagram, the red
supergiant stage (RSG), the post-red supergiant phases and the final fate of
solar metallicity stars with masses between 9 and 25 M. We examine the
impact of different initial rotation and of various prescriptions for the mass
loss rates during the red supergiant phase. We show that, whatever the initial
rotation rate (chosen between 0 and 0.7,
being the surface equatorial velocity producing a
centrifugal acceleration balancing exactly the gravity) and the mass loss rates
during the RSG stage (varied between a standard value and 25 times that value),
a 15 M star always ends its lifetime as a RSG and explodes as a type
II-P or II-L supernova.Comment: 12 pages, 5 figures, Betelgeuse workshop, November 2012, Paris. To be
published in the European Astronomical Society Publications Series, editors:
Pierre Kervella, Thibaut Le Bertre & Guy Perri
Evolution of the First Stars: CNO Yields and the C-rich Extremely Metal Poor Stars
Rotating massive stars at and lose a great part of
their initial mass through stellar winds. The chemical composition of the
rotationally enhanced winds of very low stars is very peculiar. The winds
show large CNO enhancements by factors of to , together with large
excesses of C and O and moderate amounts of Na and Al. The
excesses of primary N are particularly striking. When these ejecta from the
rotationally enhanced winds are diluted with the supernova ejecta from the
corresponding CO cores, we find [C/Fe], [N/Fe],[O/Fe] abundance ratios very
similar to those observed in the C--rich extremely metal poor stars (CEMP). We
show that rotating AGB stars and rotating massive stars have about the same
effects on the CNO enhancements. Abundances of s-process elements and the
C/C ratio could help us to distinguish between contributions from
AGB and massive stars. On the whole, we emphasize the dominant effects of
rotation for the chemical yields of extremely metal poor stars.Comment: 10 pages, 7 figures, to appear in From Lithium to Uranium: Elemental
Tracers of Early Cosmic Evolution, V. Hill, P. Francois & F. Primas, ed
Impact of rotation on stellar models
After a brief recall of the main impacts of stellar rotation on the structure
and the evolution of stars, four topics are addressed: 1) the links between
magnetic fields and rotation; 2) the impact of rotation on the age
determination of clusters; 3) the exchanges of angular momentum between the
orbit of a planet and the star due to tides; 4) the impact of rotation on the
early chemical evolution of the Milky Way and the origin of the
Carbon-Enhanced-Metal-Poor stars.Comment: 5 pages, 2 figures, To appear in Astronomische Nachrichten, special
issue "Reconstruction the Milky Way's History: Spectroscopic surveys,
Asteroseismology and Chemo-dynamical models", Guest Editors C. Chiappini, J.
Montalban, and M. Steffen, AN 2016 (in press
Effects of the variation of fundamental constants on Pop III stellar evolution
A variation of the fundamental constants is expected to affect the
thermonuclear rates important for stellar nucleosynthesis. In particular,
because of the very small resonant energies of Be8 and C12, the triple
process is extremely sensitive to any such variations. Using a microscopic
model for these nuclei, we derive the sensitivity of the Hoyle state to the
nucleon-nucleon potential allowing for a change in the magnitude of the nuclear
interaction. We follow the evolution of 15 and 60 solar mass, zero metallicity
stellar models, up to the end of core helium burning. These stars are assumed
to be representative of the first, Population III stars. We derive limits on
the variation of the magnitude of the nuclear interaction and model dependent
limits on the variation of the fine structure constant based on the calculated
oxygen and carbon abundances resulting from helium burning. The requirement
that some C12 and O16 be present are the end of the helium burning phase allows
for permille limits on the change of the nuclear interaction and limits of
order 10^{-5} on the fine structure constant relevant at a cosmological
redshift of z ~ 15-20.Comment: 14 pages, 12 figure
Four open questions in massive star evolution
We discuss four questions dealing with massive star evolution. The first one
is about the origin of slowly rotating, non-evolved, nitrogen rich stars. We
propose that these stars may originate from initially fast rotating stars whose
surface has been braked down. The second question is about the evolutionary
status of alpha-Cygni variables. According to their pulsation properties, these
stars should be post red supergiant stars. However, some stars at least present
surface abundances indicating that they should be pre red supergiant stars. How
to reconcile these two contradictory requirements? The third one concerns the
various supernova types which are the end point of the evolution of stars with
initial masses between 18 and 30 Msun, i.e. the most massive stars which go
through a red supergiant phase during their lifetime. Do they produce types
IIP, IIL, IIn, IIb or Ib supernovae or do they end without producing any SN
event? Finally, we shall discuss reasons why so few progenitors of type Ibc
supernovae have yet been detected?Comment: 10 pages, 6 figures, conference, New advances in stellar physics:
from microscopic to macroscopic processes, EAS publication serie