3,731 research outputs found
On the non-thermal kappa-distributed electrons in planetary nebulae and HII regions: the kappa index and its correlations with other nebular properties
Recently, a suspicion arose that the free electrons in planetary nebulae
(PNe) and HII regions might have non-thermal energy distributions. In this
scenario, a kappa index is introduced to characterize the electron energy
distributions, with smaller kappa values indicating larger deviations from
Maxwell-Boltzmann distributions. Assuming that this is the case, we determine
the kappa values for a sample of PNe and HII regions by comparing the
intensities of [OIII] collisionally excited lines and the hydrogen Balmer jump.
We find the average kappa indices of PNe and HII regions to be 27 and 32,
respectively. Correlations between the resultant kappa values and various
physical properties of the nebulae are examined to explore the potential origin
of non-thermal electrons in photoionized gaseous nebulae. However, no positive
result is obtained. Thus the current analysis does not lend to support to the
idea that kappa-distributed electrons are present in PNe and HII regions.Comment: 23 pages, 6 figures, accepted for publication in Ap
H I Free-Bound Emission of Planetary Nebulae with Large Abundance Discrepancies: Two-Component Models versus Kappa-distributed electrons
The "abundance discrepancy" problem in the study of planetary nebulae (PNe),
viz., the problem concerning systematically higher heavy-element abundances
derived from optical recombination lines relative to those from collisionally
excited lines, has been under discussion for decades, but no consensus on its
solution has yet been reached. In this paper we investigate the hydrogen
free-bound emission near the Balmer jump region of four PNe that are among
those with the largest abundance discrepancies, aiming to examine two recently
proposed solutions to this problem: two-component models and Kappa electron
energy distributions. We find that the Balmer jump intensities and the spectrum
slopes cannot be simultaneously matched by the theoretical calculations based
upon single Maxwell-Boltzmann electron-energy distributions, whereas the
fitting can be equally improved by introducing Kappa electron energy
distributions or an additional Maxwell-Boltzmann component. We show that
although H I free-bound emission alone cannot distinguish the two scenarios, it
can provide important constraints on the electron energy distributions,
especially for cold and low-Kappa plasmas.Comment: 23 pages, 10 figures, accepted for publication in Ap
Effects of density-dependent quark mass on phase diagram of three-flavor quark matter
Considering the density dependence of quark mass, we investigate the phase
transition between the (unpaired) strange quark matter and the
color-flavor-locked matter, which are supposed to be two candidates for the
ground state of strongly interacting matter. We find that if the current mass
of strange quark is small, the strange quark matter remains stable unless
the baryon density is very high. If is large, the phase transition from
the strange quark matter to the color-flavor-locked matter in particular to its
gapless phase is found to be different from the results predicted by previous
works. A complicated phase diagram of three-flavor quark matter is presented,
in which the color-flavor-locked phase region is suppressed for moderate
densities.Comment: 4 figure
Eight-potential-well order-disorder ferroelectric model and effects of random fields
An eight-potential-well order-disorder ferroelectric model was presented and
the phase transition was studied under the mean-field approximation. It was
shown that the two-body interactions are able to account for the first-order
and the second order phase transitions. With increasing the random fields in
the system, a first-order phase transition is transformed into a second-order
phase transition, and furthermore, a second-order phase transition is
inhibited.
However, proper random fields can promote the spontaneous appearance of a
first-order phase transition by increasing the overcooled temperature. The
connections of the model with relaxors were discussed.Comment: 8 pages, 5 figures. Submitted to Applied Physics Letter
- β¦