105 research outputs found
R Coronae Borealis Stars are Viable Factories of Pre-solar Grains
We present a new theoretical estimate for the birthrate of R Coronae Borealis
(RCB) stars that is in agreement with recent observational data. We find the
current Galactic birthrate of RCB stars to be 25% of the Galactic
rate of Type Ia supernovae, assuming that RCB stars are formed through the
merger of carbon-oxygen and helium-rich white dwarfs. Our new RCB birthrate
( yr) is a factor of 10 lower than previous
theoretical estimates. This results in roughly 180--540 RCB stars in the
Galaxy, depending on the RCB lifetime. From the theoretical and observational
estimates, we calculate the total dust production from RCB stars and compare
this rate to dust production from novae and born-again asymptotic giant branch
(AGB) stars. We find that the amount of dust produced by RCB stars is
comparable to the amounts produced by novae or born-again post-AGB stars,
indicating that these merger objects are a viable source of carbonaceous
pre-solar grains in the Galaxy. There are graphite grains with carbon and
oxygen isotopic ratios consistent with the observed composition of RCB stars,
adding weight to the suggestion that these rare objects are a source of
stardust grains.Comment: Accepted for publication in The Astrophysical Journal, 7 page
SN1991bg-like supernovae are a compelling source of most Galactic antimatter
The Milky Way Galaxy glows with the soft gamma ray emission resulting from
the annihilation of electron-positron pairs every
second. The origin of this vast quantity of antimatter and the peculiar
morphology of the 511keV gamma ray line resulting from this annihilation have
been the subject of debate for almost half a century. Most obvious positron
sources are associated with star forming regions and cannot explain the rate of
positron annihilation in the Galactic bulge, which last saw star formation some
ago, or else violate stringent constraints on the positron
injection energy. Radioactive decay of elements formed in core collapse
supernovae (CCSNe) and normal Type Ia supernovae (SNe Ia) could supply
positrons matching the injection energy constraints but the distribution of
such potential sources does not replicate the required morphology. We show that
a single class of peculiar thermonuclear supernova - SN1991bg-like supernovae
(SNe 91bg) - can supply the number and distribution of positrons we see
annihilating in the Galaxy through the decay of Ti synthesised in these
events. Such Ti production simultaneously addresses the observed
abundance of Ca, the Ti decay product, in solar system material.Comment: Accepted for publication in Proceedings of IAU Symposium 322: The
Multimessenger Astrophysics of the Galactic Center 4 page
Infrared imaging of the sub-millimetre protocluster near NGC 2068 in Orion B
ix, 91 leaves : ill. (some col.) ; 28 cm.Includes abstract and appendices.Includes bibliographical references (leaves 88-91).Sub-millimetre mapping of Orion B (L1630) using SCUBA on the James Clerk Maxwell Telescope has revealed a large population of compact cores (Mitchell et al. 2001). Using the CFHT-IR camera on the Canada-France-Hawaii Telescope, seven fields in NGC 2068 in Orion B were imaged in the near-infrared, both in a narrowband K continuum filter (2.260 μm) and in a narrow filter centred on the 2.122 μm line of H₂. The infrared images show many non-stellar and resolved features near several of the SCUBA cores, indicating the presence of embedded stellar objects and shock-excited gas.
We compare the infrared maps with the 850 μm sub-millimetre map, as well as a previously obtained map of CO J = 3-2 gas and H₂CO spectra in order to assess the likelihood of star formation for each SCUBA core
The contribution of halo white dwarf binaries to the laser interferometer space antenna signal
Galactic double white dwarfs were postulated as a source of confusion limited noise for the Laser Interferometer Space Antenna (LISA), the future space-based gravitational wave observatory. Until very recently, the Galactic population consisted of a relatively well-studied disk population, a somewhat studied smaller bulge population and a mostly unknown, but potentially large halo population. It has been argued that the halo population may produce a signal that is much stronger (factor of ∼5 in spectral amplitude) than the disk population. However, this surprising result was not based on an actual calculation of a halo white dwarf population, but was derived on (1) the assumption that one can extrapolate the halo population properties from those of the disk population and (2) the postulated (unrealistically) high number of white dwarfs in the halo. We perform the first calculation of a halo white dwarf population using population synthesis models. Our comparison with the signal arising from double white dwarfs in the Galactic disk+bulge clearly shows that it is impossible for the double white dwarf halo signal to exceed that of the rest of the Galaxy. Using microlensing results to give an upper limit on the content of white dwarfs in the halo (∼30% baryonic mass in white dwarfs), our predicted halo signal is a factor of 10 lower than the disk+bulge signal. Even in the implausible case, where all of the baryonic halo mass is found in white dwarfs, the halo signal does not become comparable to that of the disk+bulge, and thus would still have a negligible effect on the detection of other LISA sources. © 2009. The American Astronomical Society. All rights reserved
PopCORN: Hunting down the differences between binary population synthesis codes
Binary population synthesis (BPS) modelling is a very effective tool to study the evolution and properties of various types of close binary systems. The uncertainty in the parameters of the model and their effect on a population can be tested in a statistical way, which then leads to a deeper understanding of the underlying (sometimes poorly understood) physical processes involved. Several BPS codes exist that have been developed with different philosophies and aims. Although BPS has been very successful for studies of many populations of binary stars, in the particular case of the study of the progenitors of supernovae Type Ia, the predicted rates and ZAMS progenitors vary substantially between different BPS codes
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