2,824 research outputs found
Newly discovered halos and outer features around southern planetary nebulae
We have used the SuperCOSMOS H-alpha Survey to look for faint outer
structures such as halos, ansae and jets around known planetary nebulae across
4000 square degrees of the southern Milky Way. Our search will contribute to a
more accurate census of these features in the Galactic PN population. Candidate
common-envelope PNe have also been identified on the basis of their
microstructures. We also intend to determine more reliable distances for these
PNe, which should allow a much better statistical basis for the post-AGB total
mass budget. Our survey offers fresh scope to address this important issue.Comment: 2 pages, 1 figure. To be published in Planetary Nebulae: an Eye to
the Future, Proceedings of IAU Symposium 283, held in Puerto de la Cruz,
Tenerife, Spain, July 25-29 201
The dynamics of planetary nebulae in the Galaxy: evidence for a third integral
We present a dynamical analysis of 673 galactic Planetary Nebulae, using a
two-integral axisymmetric model with a Kuzmin-Kutuzov St\"{a}ckel potential.
The method fits the kinematics to the projected moments of a distribution
function, by means of Quadratic Programming. The 2.2 m COBE brightness map
has been used after correction for the interstellar extinction as a projected
star counts map in the modeling, because it constitutes a galactic distribution
view of evolved red populations which are considered to be the progenitors of
PNe. The model we have obtained provides a 2-integral distribution function for
the COBE 2.2 m map, and thus {\it a fortiori} a deprojection of it, which
allows moreover the identification of all the major Galactic components. We
derive the density laws for them. The projected velocity dispersions are not
well fitted though, especially in the disk, which points at the likely presence
of a third integral. If this result can be confirmed by additional data, this
would mean that for the first time the presence and importance of a third
integral on a global scale is demonstrated.Comment: 9 pages, uuencoded gzipped postscript file, 9 figures include
Constraints on decay plus oscillation solutions of the solar neutrino problem
We examine the constraints on non-radiative decay of neutrinos from the
observations of solar neutrino experiments. The standard oscillation hypothesis
among three neutrinos solves the solar and atmospheric neutrino problems. Decay
of a massive neutrino mixed with the electron neutrino results in the depletion
of the solar neutrino flux. We introduce neutrino decay in the oscillation
hypothesis and demand that decay does not spoil the successful explanation of
solar and atmospheric observations. We obtain a lower bound on the ratio of the
lifetime over the mass of , (\tau_2/m_2) > 22.7 (\srm/\MeV) for the
MSW solution of the solar neutrino problem and (\tau_2/m_2) > 27.8
(\srm/\MeV) for the VO solution (at 99% C.L.).Comment: 8 pages latex file with 4 figure
MSW mediated neutrino decay and the solar neutrino problem
We investigate the solar neutrino problem assuming simultaneous presence of
MSW transitions in the sun and neutrino decay on the way from sun to earth. We
do a global -analysis of the data on total rates in Cl, Ga and
Superkamiokande (SK) experiments and the SK day-night spectrum data and
determine the changes in the allowed region in the \dm - \tan^2\theta plane
in presence of decay. We also discuss the implications for unstable neutrinos
in the SNO experiment.Comment: Final version to appear in Phys. Rev.
The true nature of the alleged planetary nebula W16-185
We report the discovery of a small cluster of massive stars embedded in a NIR
nebula in the direction of the IRAS15411-5352 point source, which is related to
the alleged planetary nebula W16-185. The majority of the stars present large
NIR excess characteristic of young stellar objects and have bright counterparts
in the Spitzer IRAC images; the most luminous star (IRS1) is the NIR
counterpart of the IRAS source. We found very strong unresolved Brgamma
emission at the IRS1 position and more diluted and extended emission across the
continuum nebula. From the sizes and electron volume densities we concluded
that they represent ultra-compact and compact HII regions, respectively.
Comparing the Brgamma emission with the 7 mm free-free emission, we estimated
that the visual extinction ranges between 14 and 20 mag. We found that only one
star (IRS1) can provide the number of UV photons necessary to ionize the
nebula.Comment: 30 pages, 15 figures, 2 tables V3: minor grammatical changes. Figure
4 is available in pdf file. Accepted for publication in AJ, April / 200
Neutrino Anomalies without Oscillations
I review explanations for the three neutrino anomalies (solar, atmospheric
and LSND) which go beyond the ``conventional'' neutrino oscillations induced by
mass-mixing. Several of these require non-zero neutrino masses as well.Comment: 14pages, LATEX format, 3 figure
A Common Explanation for the Atmospheric, Solar-Neutrino and Double Beta Decay Anomalies
We make a number of small changes, including correcting an error in our
heavy-neutrino decay rate. None of our analysis is changed, either in substance
or detail.Comment: 25 pages, 6 Figures, McGill-93/1
K_L \ra \mu^\pm e^\mp \nu \overline{\nu} as background to K_L \ra \mu^\pm e^\mp
We consider the process K_L \ra \mu^\pm e^\mp \nu \overline{\nu} at next to
leading order in chiral perturbation theory. This process occurs in the
standard model at second order in the weak interaction and constitutes a
potential background in searches for new physics through the modes K_L \ra
\mu^\pm e^\mp. We find that the same cut, ~MeV, used to remove
the sequential decays K_{l3}\ra \pi_{l2} pushes the B(K_L \ra \mu^\pm e^\mp
\nu \overline{\nu}) to the level, effectively removing it as a
background.Comment: 8 pages, LaTeX, 1 figure appended as postscript file after
\end{document}. Fermilab-Pub-93/024-
Decay of High-Energy Astrophysical Neutrinos
Existing limits on the non-radiative decay of one neutrino to another plus a
massless particle (e.g., a singlet Majoron) are very weak. The best limits on
the lifetime to mass ratio come from solar neutrino observations, and are
\tau/m \agt 10^{-4} s/eV for the relevant mass eigenstate(s). For lifetimes
even several orders of magnitude longer, high-energy neutrinos from distant
astrophysical sources would decay. This would strongly alter the flavor ratios
from the expected
from oscillations alone, and should be readily visible in the near future in
detectors such as IceCube.Comment: 4 pages, 1 figure. References added. Version to appear in PR
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