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Dieter H Hartmann

Publications and source records attributed to Dieter H Hartmann.

5 recordsLinked to original sources
PubMed2006

Supernova neutrino nucleosynthesis of light elements with neutrino oscillations.

Light element synthesis in supernovae through neutrino-nucleus interactions, i.e., the v process, is affected by neutrino oscillations in the supernova environment. There is a resonance of 13-mixing in the O/C layer, which increases the rates of charged-current -process reactions in the outer He-rich layer. The yields of 7Li and 11B increase by about a factor of 1.9 and 1.3, respectively, for a normal mass hierarchy and an adiabatic 13-mixing resonance, compared to those without neutrino oscillations. In the case of an inverted mass hierarchy and a nonadiabatic 13-mixing resonance, the increase in the 7Li and 11B yields is much smaller. Observations of the 7Li/11B ratio in stars showing signs of supernova enrichment could thus provide a unique test of neutrino oscillations and constrain their parameters and the mass hierarchy.

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PubMed2006

Radioactive 26Al from massive stars in the Galaxy.

Gamma-rays from radioactive 26Al (half-life approximately 7.2 x 10(5) years) provide a 'snapshot' view of continuing nucleosynthesis in the Galaxy. The Galaxy is relatively transparent to such gamma-rays, and emission has been found concentrated along its plane. This led to the conclusion that massive stars throughout the Galaxy dominate the production of 26Al. On the other hand, meteoritic data show evidence for locally produced 26Al, perhaps from spallation reactions in the protosolar disk. Furthermore, prominent gamma-ray emission from the Cygnus region suggests that a substantial fraction of Galactic 26Al could originate in localized star-forming regions. Here we report high spectral resolution measurements of 26Al emission at 1808.65 keV, which demonstrate that the 26Al source regions corotate with the Galaxy, supporting its Galaxy-wide origin. We determine a present-day equilibrium mass of 2.8 (+/- 0.8) solar masses of 26Al. We use this to determine that the frequency of core collapse (that is, type Ib/c and type II) supernovae is 1.9 (+/- 1.1) events per century.

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PubMed2005

Constraining the spectrum of supernova neutrinos from nu-process induced light element synthesis.

We constrain energy spectra of supernova neutrinos through the avoidance of an overproduction of the 11B abundance during Galactic chemical evolution. In supernova nucleosynthesis calculations with a parametrized neutrino spectrum as a function of temperature of nu(mu,tau) and nu(mu,tau) and total neutrino energy, we find a strong neutrino temperature dependence of the 11B yield. When the yield is combined with observed abundances, the acceptable range of the nu(mu,tau) and nu(mu,tau) temperature is found to be 4.8 to 6.6 MeV. Nonzero neutrino chemical potentials would reduce this temperature range by about 10% for a degeneracy parameter eta(nu) = mu(nu)/kT(nu) smaller than 3.

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PubMed2003

Evolution of the polarization of the optical afterglow of the gamma-ray burst GRB030329.

The association of a supernova with GRB030329 strongly supports the 'collapsar' model of gamma-ray bursts, where a relativistic jet forms after the progenitor star collapses. Such jets cannot be spatially resolved because gamma-ray bursts lie at cosmological distances; their existence is instead inferred from 'breaks' in the light curves of the afterglows, and from the theoretical desire to reduce the estimated total energy of the burst by proposing that most of it comes out in narrow beams. Temporal evolution of the polarization of the afterglows may provide independent evidence for the jet structure of the relativistic outflow. Small-level polarization ( approximately 1-3 per cent) has been reported for a few bursts, but its temporal evolution has yet to be established. Here we report polarimetric observations of the afterglow of GRB030329. We establish the polarization light curve, detect sustained polarization at the per cent level, and find significant variability. The data imply that the afterglow magnetic field has a small coherence length and is mostly random, probably generated by turbulence, in contrast with the picture arising from the high polarization detected in the prompt gamma-rays from GRB021206 (ref. 18).

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