326 research outputs found
Progenitors of Core-Collapse Supernovae
The progenitors of core-collapse supernovae are stars with an initial mass
greater than about 8M(sun). Understanding the evolution of these stars is
necessary to comprehend the evolution and differences between supernovae.
We have constructed new and unique opacity tables to increase model accuracy
during the latest stages of stellar evolution. We have investigated how initial
mass, initial composition and mass loss affects the progenitors and their
populations. There are many prescriptions for mass loss. Different research
groups use their preferred rates. We have compared 12 different prescriptions
and determined which provides the best fit to observations. We use our
preferred mass-loss scheme to make suggestions as to the source of the
differences between supernova types from our progenitor models.
Binary evolution is considered in order to search for low luminosity SN
progenitors and progenitor types not possible from single stars. Removal of the
hydrogen envelope is more common and we find quite different hydrogen deficient
SN progenitors. We discuss the implications of our binary models for
ultra-luminous X-ray sources and gamma-ray bursts. We present an estimation of
the mass distribution for black holes at various metallcities showing that
massive black holes are not formed until very low metallicities. Finally we
combine the single star and binary results to determine their relative
populations and compare to observations. However it is not possible to draw
many firm conclusions because of the uncertainty in observations to date.Comment: PhD Thesis, 171 pages, low detail figures, appendices removed to fit
onto arXiv.org. For high resolution figures and the appendices goto
http://www.iap.fr/users/eldridge/public.htm
The death of massive stars - II. Observational constraints on the progenitors of type Ibc supernovae
The progenitors of many type II core-collapse supernovae have now been
identified directly on pre-discovery imaging. Here we present an extensive
search for the progenitors of type Ibc supernovae in all available
pre-discovery imaging since 1998. There are 12 type Ibc supernovae with no
detections of progenitors in either deep ground-based or Hubble Space Telescope
archival imaging. The deepest absolute BVR magnitude limits are between -4 and
-5. We compare these limits with the observed Wolf-Rayet population in the
Large Magellanic Cloud and estimate a 16 per cent probability we have failed to
detect such a progenitor by chance. Alternatively the progenitors evolve
significantly before core-collapse or we have underestimated the extinction
towards the progenitors. Reviewing the relative rates and ejecta mass estimates
from lightcurve modelling of Ibc SNe, we find both incompatible with Wolf-Rayet
stars with initial masses >25Msun being the only progenitors. We present binary
evolution models that fit these observational constraints. Stars in binaries
with initial masses <20Msun lose their hydrogen envelopes in binary
interactions to become low mass helium stars. They retain a low mass hydrogen
envelope until approximately 10,000 years before core-collapse; hence it is not
surprising that galactic analogues have been difficult to identify.Comment: Accepted by MNRAS. 31 pages, 12 figures, 8 table
Gender Differences in Attitudes Toward Animal Research
Although gender differences in attitudes toward animal research have been reported in the literature for some time, exploration into the nature of these differences has received less attention. This article examines gender differences in responses to a survey of attitudes toward the use of animals in research. The survey was completed by college students and consisted of items intended to tap different issues related to the animal research debate. Results indicated that women were more likely than men to support tenets of the animal protection movement. Likewise, women were more likely than men to favor increased restrictions on animal use and were more concerned than men about the suffering of research animals. Analysis of item contents suggested that women endorsed items reflecting a general caring for animals, were more willing than men to make personal sacrifices such as giving up meat and medical benefits in an effort to protect animals, and were more likely than men to question the use of animals in research on scientific grounds. Men, on the other hand, tended to emphasize the potential benefits arising from the use of animals in research
Gender Differences in Attitudes Toward Animal Research
Although gender differences in attitudes toward animal research have been reported in the literature for some time, exploration into the nature of these differences has received less attention. This article examines gender differences in responses to a survey of attitudes toward the use of animals in research. The survey was completed by college students and consisted of items intended to tap different issues related to the animal research debate. Results indicated that women were more likely than men to support tenets of the animal protection movement. Likewise, women were more likely than men to favor increased restrictions on animal use and were more concerned than men about the suffering of research animals. Analysis of item contents suggested that women endorsed items reflecting a general caring for animals, were more willing than men to make personal sacrifices such as giving up meat and medical benefits in an effort to protect animals, and were more likely than men to question the use of animals in research on scientific grounds. Men, on the other hand, tended to emphasize the potential benefits arising from the use of animals in research
Mass loss and supernova progenitors
We first discuss the mass range of type IIP SN progenitors and how the upper
and lower limits impose interesting constraints on stellar evolution. Then we
discuss the possible implications of two SNe, 2002ap and 2006jc, for Wolf-Rayet
star mass-loss rates and long Gamma-ray bursts.Comment: 7 pages, 3 figures, to appear in the Conference Proceedings of
"Unsolved Problems in Stellar Astrophysics
Circumstellar dust as a solution to the red supergiant supernova progenitor problem
We investigate the red supergiant problem: the apparent dearth of Type IIP
supernova progenitors with masses between 16 and 30 M_sun. Although red
supergiants with masses in this range have been observed, none have been
identified as progenitors in pre-explosion images. We show that by failing to
take into account the additional extinction resulting from the dust produced in
the red supergiant winds, we risk underestimating the luminosity of the most
massive red supergiants at the end of their lives. We estimate the initial
masses of all Type IIP progenitors for which observations exist and analyse the
resulting population. We find that the most likely maximum mass for a Type IIP
progenitor is 21^{+2}_{-1} M_sun. This is in closer agreement with the limit
predicted from single star evolution models.Comment: 10 pages, 6 figures and 4 tables. Accepted for publication in MNRA
Characterizing Supernova Progenitors via the Metallicities of their Host Galaxies, from Poor Dwarfs to Rich Spirals
We investigate how the different types of supernovae are relatively affected
by the metallicity of their host galaxy. We match the SAI Supernova Catalog to
the SDSS-DR4 catalog of star-forming galaxies with measured metallicities.
These supernova host galaxies span a range of oxygen abundance from 12 +
log(O/H) = 7.9 to 9.3 (~ 0.1 to 2.7 solar) and a range in absolute magnitude
from MB = -15.2 to -22.2. To reduce the various observational biases, we select
a subsample of well-characterized supernovae in the redshift range from 0.01 to
0.04, which leaves us with 58 SN II, 19 Ib/c, and 38 Ia. We find strong
evidence that SN Ib/c are occurring in higher-metallicity host galaxies than SN
II, while we see no effect for SN Ia relative to SN II. We note some extreme
and interesting supernova-host pairs, including the metal-poor (~ 1/4 solar)
host of the recent SN Ia 2007bk, where the supernova was found well outside of
this dwarf galaxy. To extend the luminosity range of supernova hosts to even
fainter galaxies, we also match all the historical supernovae with z < 0.3 to
the SDSS-DR6 sky images, resulting in 1225 matches. This allows us to identify
some even more extreme cases, such as the recent SN Ic 2007bg, where the likely
host of this hypernova-like event has an absolute magnitude MB ~ -12, making it
one of the least-luminous supernova hosts ever observed. This low-luminosity
host is certain to be very metal poor (~ 1/20 solar), and therefore this
supernova is an excellent candidate for association with an off-axis GRB. The
two catalogs that we have constructed are available online and will be updated
regularly. Finally, we discuss various implications of our findings for
understanding supernova progenitors and their host galaxies.Comment: ApJ accepted, 26 pages, 5 figures, 1 table. Updated catalogs are
available at http://www.astronomy.ohio-state.edu/~prieto/snhosts
The red supergiants & Wolf-Rayet stars of NGC 604
We study the post-main sequence stars in NGC 604, the most luminous HII
region in M33. Previously, a number of Wolf-Rayet (WR) stars and one red
supergiant (RSG) have been discovered. Based on broadband photometry of the
region, we present evidence that is consistent with the presence of this RSG
and with three more RSG candidates. Using SED fitting based on HST UVIJHK
photometry we estimate the ages of the WR stars and RSGs finding that the two
populations are from distinct formation episodes with ages 3.2\pm\pm$ 0.6) x
10^5Msun. We find a large discrepancy between the expected H{\alpha} flux from
such a massive cluster and that one observed. This suggests that 49 (+16,-19)
percent of the ionizing photons produced by massive stars in NGC 604 is leaking
from this HII region. We also suggest that the implications of an old RSG
population mean that if NGC 604 was more distant and only observed in the
infrared (IR) it would be difficult to study the youngest burst of star
formation due to the contamination of RSGs.Comment: Accepted for publication in MNRAS, 13 pages, 10 figures, 3 table
Accessory cells in Murine Peyer’s patch: I. Identification and enrichment of a functional dendritic cell
[No abstract available
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