115 research outputs found
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
First Stars III Conference Summary
The understanding of the formation, life, and death of Population III stars,
as well as the impact that these objects had on later generations of structure
formation, is one of the foremost issues in modern cosmological research and
has been an active area of research during the past several years. We summarize
the results presented at "First Stars III," a conference sponsored by Los
Alamos National Laboratory, the Kavli Institute for Particle Astrophysics and
Cosmology, and the Joint Institute for Nuclear Astrophysics. This conference,
the third in a series, took place in July 2007 at the La Fonda Hotel in Santa
Fe, New Mexico, U.S.A.Comment: 11 pages, no figures; Conference summary for First Stars III, which
was held in Santa Fe, NM on July 15-20, 2007. To appear in "Proceedings of
First Stars III," Eds. Brian W. O'Shea, Alexander Heger & Tom Abe
ADDA: a domain database with global coverage of the protein universe
We used the Automatic Domain Decomposition Algorithm (ADDA) to generate a database of protein domain families with complete coverage of all protein sequences. Sequences are split into domains and domains are grouped into protein domain families in a completely automated process. The current database contains domains for more than 1.5 million sequences in more than 40 000 domain families. In particular, there are 3828 novel domain families that do not overlap with the curated domain databases Pfam, SCOP and InterPro. The data are freely available for downloading and querying via a web interface (http://ekhidna.biocenter.helsinki.fi:9801/sqgraph/pairsdb)
The effect of massive binaries on stellar populations and supernova progenitors
We compare our latest single and binary stellar model results from the
Cambridge STARS code to several sets of observations. We examine four stellar
population ratios, the number of blue to red supergiants, the number of
Wolf-Rayet stars to O supergiants, the number of red supergiants to Wolf-Rayet
stars and the relative number of Wolf-Rayet subtypes, WC to WN stars. These
four ratios provide a quantitative measure of nuclear burning lifetimes and the
importance of mass loss during various stages of the stars' lifetimes. In
addition we compare our models to the relative rate of type Ib/c to type II
supernovae to measure the amount of mass lost over the entire lives of all
stars. We find reasonable agreement between the observationally inferred values
and our predicted values by mixing single and binary star populations. However
there is evidence that extra mass loss is required to improve the agreement
further, to reduce the number of red supergiants and increase the number of
Wolf-Rayet stars.Comment: Accepted for publication in MNRAS, 11 pages, 10 figure
Spindown of massive rotating stars
Models of rapidly rotating massive stars at low metallicities show
significantly different evolution and higher metal yields compared to
non-rotating stars. We estimate the spin-down time-scale of rapid rotating
non-convective stars supporting an alpha-Omega dynamo. The magnetic dynamo
gives rise to mass loss in a magnetically controlled stellar wind and hence
stellar spin down owing to loss of angular momentum. The dynamo is maintained
by strong horizontal rotation-driven turbulence which dominates over the Parker
instability. We calculate the spin-down time-scale and find that it could be
relatively short, a small fraction of the main-sequence lifetime. The spin-down
time-scale decreases dramatically for higher surface rotations suggesting that
rapid rotators may only exhibit such high surface velocities for a short time,
only a small fraction of their main-sequence lifetime.Comment: Accepted by MNRA
- …