38 research outputs found
Stellar Abundances in the Early Galaxy and Two r-Process Components
We present quantitative predictions for the abundances of r-process elements
in stars formed very early in the Galactic history using a phenomenological
two-component r-process model based on the I129 and Hf182 inventory in the
early solar system. This model assumes that a standard mass of the ISM dilutes
the debris from an individual supernova. High frequency supernova H events and
low frequency supernova L events are proposed in the model with characteristics
determined by the meteoritic data on I129 and Hf182. The yields in an H or L
event are obtained from these characteristics and the solar r-process
abundances under the assumption that the yield template for the high mass (A >
130) nuclei associated with W182 or the low mass (A < or = 130) nuclei
associated with I127 is the same for both the H and L events and follows the
corresponding solar r-pattern in each mass region. The abundance of Eu, not Fe,
is proposed as a key guide to the age of very metal-poor stars. We predict that
stars with log epsilon (Eu) = -2.98 to -2.22 were formed from an ISM
contaminated most likely by a single H event within the first 10**7 yr of the
Galactic history and should have an Ag/Eu abundance ratio less than the
corresponding solar r-process value by a factor of at least 10. Many of the
very metal-poor stars observed so far are considered here to have been formed
from an ISM contaminated by many (about 10) r-process events. Stars formed from
an ISM contaminated only by a pure L event would have an Ag/Eu ratio higher
than the corresponding solar r-process value but would be difficult to find due
to the low frequency of the L events. However, variations in the relative
abundances of the low and high mass regions should be detectable in very
metal-poor stars.Comment: 46 pages, 19 figures, to appear in the Schramm Memorial Volume of
Physics Report
Short-lived Nuclei in the Early Solar System: Possible AGB Sources
(Abridged) We review abundances of short-lived nuclides in the early solar
system (ESS) and the methods used to determine them. We compare them to the
inventory for a uniform galactic production model. Within a factor of two,
observed abundances of several isotopes are compatible with this model. I-129
is an exception, with an ESS inventory much lower than expected. The isotopes
Pd-107, Fe-60, Ca-41, Cl-36, Al-26, and Be-10 require late addition to the
solar nebula. Be-10 is the product of particle irradiation of the solar system
as probably is Cl-36. Late injection by a supernova (SN) cannot be responsible
for most short-lived nuclei without excessively producing Mn-53; it can be the
source of Mn-53 and maybe Fe-60. If a late SN is responsible for these two
nuclei, it still cannot make Pd-107 and other isotopes. We emphasize an AGB
star as a source of nuclei, including Fe-60 and explore this possibility with
new stellar models. A dilution factor of about 4e-3 gives reasonable amounts of
many nuclei. We discuss the role of irradiation for Al-26, Cl-36 and Ca-41.
Conflict between scenarios is emphasized as well as the absence of a global
interpretation for the existing data. Abundances of actinides indicate a
quiescent interval of about 1e8 years for actinide group production in order to
explain the data on Pu-244 and new bounds on Cm-247. This interval is not
compatible with Hf-182 data, so a separate type of r-process is needed for at
least the actinides, distinct from the two types previously identified. The
apparent coincidence of the I-129 and trans-actinide time scales suggests that
the last actinide contribution was from an r-process that produced actinides
without fission recycling so that the yields at Ba and below were governed by
fission.Comment: 92 pages, 14 figure files, in press at Nuclear Physics
The Role of Radioactivities in Astrophysics
I present both a history of radioactivity in astrophysics and an introduction
to the major applications of radioactive abundances to astronomy
Recommended from our members
Aquifer transport of Th, U, Ra, and Rn in solution and on colloids. 1998 annual progress report
'The investigation focuses on understanding the behavior of naturally occurring U, Th, Ra, and Rn isotopes in groundwater along with the supply rates of these isotopes by rock alteration, and utilizing these species as natural analogues for waste radionuclides, thereby providing a basis for predicting contaminant migration behavior in potentially impacted aquifers. The study examines the fundamental controls on natural radionuclide transport in specific aquifers by integrating aquifer sample analyses, focused laboratory experiments, field observations, and theoretical modeling.
Stars, gas, dust and planets
Item consists of a digitized copy of an audio recording of a Cecil and Ida Green lecture presented at the Vancouver Institute by G.J. Wassberg on April 3, 1982. Original audio recording available in the University Archives (UBC AT 1012).Other UBCUnreviewedOthe