3,676 research outputs found
J08069+1527: A newly discovered high amplitude, hybrid subdwarf B pulsator
We present our discovery of a new hybrid pulsating subdwarf B star,
J08069+1527. The effective temperature and surface gravity of 28,500400\,K
and 5.370.04\,dex, respectively, place this object inside the instability
strip and also among other pulsating hot subdwarfs of a hybrid nature, right
next to another fascinating star: Balloon\,090100001. From this proximity, we
anticipated this star could pulsate in both high and low frequency modes.
Indeed, our analysis of photometric data confirmed our prediction. We detected
two peaks in the high frequency region and two other peaks at low frequencies.
In addition, the amplitude of the dominant mode is very high and comparable to
the dominant peaks in other hybrid subdwarf B stars. Since this star is bright,
we performed time-series low resolution spectroscopy. Despite a low
signal-to-noise (S/N) ratio, we were able to detect the main peak from these
data. All our results strongly indicate that J08069+1527 is a high amplitude
pulsating hot subdwarf B star of hybrid nature. By analogy to the other
pulsating sdB star, we judge that the dominant mode we detected here has radial
nature. Future stellar modeling should provide us with quite good constrains as
p- and g-modes presented in this star are driven in different parts of its
interior.Comment: 7 pages, 10 figures, accepted for publication in MNRA
Does the NJL chiral phase transition affect the elliptic flow of a fluid at fixed ?
We have derived and solved numerically the Boltzmann-Vlasov transport
equations that includes both two-body collisions and the chiral phase
transition by mean of NJL-field dynamics. The scope is to understand if the
field dynamics supply new genuine effects on the build-up of the elliptic flow
, a measure of the asymmetry in the momentum space, and in particular if
it can affect the relation between and the shear viscosity to entropy
ratio . Solving the transport equation with a constant cross section
for the condition of collisions at AGeV it is shown
a sizable suppression of due to the attractive nature of the field
dynamics that generates the constituent mass. However the key result is that if
of the system is kept fixed by an appropriate local renormalization of
the cross section the does not depend on the details of the collisional
and/or field dynamics and in particular it is not affected significantly by the
chiral phase transition.Comment: 5 pages, 5 figure
Asymmetry Effects on Nuclear Fragmentation
We show the possibility of extracting important information on the symmetry
term of the Equation of State () directly from multifragmentation
reactions using stable isotopes with different charge asymmetries. We study
n-rich and n-poor collisions at using a new stochastic
transport approach with all isospin effects suitably accounted for. For central
collisions a chemical component in the spinodal instabilities is clearly seen.
This effect is reduced in the neck fragmentation observed for semiperipheral
collisions, pointing to a different nature of the instability. In spite of the
low asymmetry tested with stable isotopes the results are showing an
interesting and promising dependence on the stiffness of the symmetry term,
with an indication towards an increase of the repulsion above normal density.Comment: 8 pages (Latex), 7 Postscript figures, CRIS2000 Conference,
Acicastello, Italy, May 22-26, (2000), Nucl. Phys. A (in press
RAT J0455+1305: A rare hybrid pulsating subdwarf B star
We present results on the second-faintest pulsating subdwarf B (sdB) star
known, RAT J0455+1305, derived from photometric data obtained in 2009. It shows
both short and long periods oscillations, theoretically assigned as pressure
and gravity modes. We identify six short-period frequencies (with one being a
combination) and six long-period frequencies. This star is the fourth hybrid
sdB star discovered so far which makes it of special interest as each type of
mode probes a different part of the star. This star is similar to the sdB
hybrid pulsator Balloon 090100001 in that it exhibits short-period mode
groupings, which can be used to identify pulsation parameters and constrain
theoretical models.Comment: published in MNRA
Electronic structure and transport properties of CeNi9In2
We investigated CeNi9In2 compound, which has been considered as a mixed
valence (MV) system. Electrical resistivity vs. temperature variation was
analysed in terms of the model proposed by Freimuth for systems with unstable
4f shell. At low temperature the resistivity dependence is consistent with a
Fermi liquid state with a contribution characteristic of electron-phonon
interaction. Ultraviolet photoemission spectroscopy (UPS) studies of the
valence band did not reveal a Kondo peak down to 14 K. A difference of the
spectra obtained with photon energies of low and high photoionization cross
sections for Ce 4f electrons indicated that 4f states are located mainly close
to the Fermi energy. The peaks related to f_{5/2}^1 and f_{7/2}^1 final states
cannot be resolved but form a plateau between -0.3 eV and the Fermi energy.
X-ray photoemission spectroscopy (XPS) studies were realized for the cerium 3d
level. The analysis of XPS spectra within the Gunnarsson-Sh\"onhammer theory
yielded a hybridization parameter of 104 meV and non-integer f level
occupation, being close to 3. Calculations of partial densities of states were
realized by a full potential local orbital (FPLO) method. They confirm that the
valence band is dominated by Ni 3d states and are in general agreement with the
experiment except for the behavior of f-electrons.Comment: 10 pages, 5 figure
Symmetry Energy Effects on the Mixed Hadron-Quark Phase at High Baryon Density
The phase transition of hadronic to quark matter at high baryon and isospin
density is analyzed. Relativistic mean field models are used to describe
hadronic matter, and the MIT bag model is adopted for quark matter. The
boundaries of the mixed phase and the related critical points for symmetric and
asymmetric matter are obtained. Due to the different symmetry term in the two
phases, isospin effects appear to be rather significant. With increasing
isospin asymmetry the binodal transition line of the (T,\rho_B) diagram is
lowered to a region accessible through heavy ion collisions in the energy range
of the new planned facilities, e.g. the FAIR/NICA projects. Some observable
effects are suggested, in particular an "Isospin Distillation" mechanism with a
more isospin asymmetric quark phase, to be seen in charged meson yield ratios,
and an onset of quark number scaling of the meson/baryon elliptic flows. The
presented isospin effects on the mixed phase appear to be robust with respect
to even large variations of the poorly known symmetry term at high baryon
density in the hadron phase. The dependence of the results on a suitable
treatment of isospin contributions in effective QCD Lagrangian approaches, at
the level of explicit isovector parts and/or quark condensates, is finally
discussed.Comment: 14 two column pages, 14 figures, new results with other hadron EoS.
Accepted for publication in Phys.Rev.
- …