75,383 research outputs found
Chemical abundances in Galactic planetary nebulae with Spitzer spectra
We present new low-resolution (R~800) optical spectra of 22 Galactic PNe with
Spitzer spectra. These data are combined with recent optical spectroscopic data
available in the literature to construct representative samples of compact (and
presumably young) Galactic disc and bulge PNe with Spitzer spectra. Attending
to the nature of the dust features seen in their Spitzer spectra, Galactic disc
and bulge PNe are classified according to four major dust types (oxygen
chemistry or OC, carbon chemistry or CC, double chemistry or DC, featureless or
F) and subtypes (amorphous and crystalline, and aliphatic and aromatic).
Nebular gas abundances of He, N, O, Ne, S, Cl, and Ar, as well as plasma
parameters (e.g. Ne, Te) are homogeneously derived and we study the median
chemical abundances and nebular properties in Galactic disc and bulge PNe
depending on their Spitzer dust types and subtypes. A comparison of the derived
median abundance patterns with AGB nucleosynthesis predictions show mainly that
i) DC PNe, both with amorphous and crystalline silicates, display
high-metallicity (solar/supra-solar) and the highest He abundances and N/O
ratios, suggesting relatively massive (~3-5 M_sun) hot bottom burning AGB stars
as progenitors; ii) PNe with O-rich and C-rich unevolved dust (amorphous and
aliphatic) seem to evolve from subsolar metallicity (z~0.008) and lower mass
(<3 M_sun) AGB stars; iii) a few O-rich PNe and a significant fraction of
C-rich PNe with more evolved dust (crystalline and aromatic, respectively)
display chemical abundances similar to DC PNe, suggesting that they are related
objects. A comparison of the derived nebular properties with predictions from
models combining the theoretical central star evolution with a simple nebular
model is also presented. Finally, a possible link between the Spitzer dust
properties, chemical abundances, and evolutionary status is discussed.Comment: Accepted for publication in Astronomy & Astrophysics (45 pages, 17
figures, and 14 tables); final version (language corrected
Ultraluminous X-ray sources with flat-topped noise and QPO
We analyzed the X-ray power density spectra of five ultraluminous X-ray
sources (ULXs) NGC5408 X-1, NGC6946 X-1, M82 X-1, NGC1313 X-1 and IC342 X-1
that are the only ULXs which display both flat-topped noise (FTN) and
quasi-periodic oscillations (QPO). We studied the QPO frequencies, fractional
root-mean-square (rms) variability, X-ray luminosity and spectral hardness. We
found that the level of FTN is anti-correlated with the QPO frequency. As the
frequency of the QPO and brightness of the sources increase, their fractional
variability decreases. We propose a simple interpretation using the
spherizarion radius, viscosity time and -parameter as basic properties
of these systems. The main physical driver of the observed variability is the
mass accretion rate which varies >3 between different observations of the same
source. As the accretion rate decreases the spherization radius reduces and the
FTN plus the QPO move toward higher frequencies resulting in a decrease of the
fractional rms variability. We also propose that in all ULXs when the accretion
rate is low enough (but still super-Eddington) the QPO and FTN disappear.
Assuming that the maximum X-ray luminosity depends only on the black hole (BH)
mass and not on the accretion rate (not considering the effects of either the
inclination of the super-Eddington disc nor geometrical beaming of radiation)
we estimate that all the ULXs have about similar BH masses, with the exception
of M82 X-1, which might be 10 times more massive.Comment: 15 pages, 7 figures, accepted for publication in MNRA
Daily Stress Recognition from Mobile Phone Data, Weather Conditions and Individual Traits
Research has proven that stress reduces quality of life and causes many
diseases. For this reason, several researchers devised stress detection systems
based on physiological parameters. However, these systems require that
obtrusive sensors are continuously carried by the user. In our paper, we
propose an alternative approach providing evidence that daily stress can be
reliably recognized based on behavioral metrics, derived from the user's mobile
phone activity and from additional indicators, such as the weather conditions
(data pertaining to transitory properties of the environment) and the
personality traits (data concerning permanent dispositions of individuals). Our
multifactorial statistical model, which is person-independent, obtains the
accuracy score of 72.28% for a 2-class daily stress recognition problem. The
model is efficient to implement for most of multimedia applications due to
highly reduced low-dimensional feature space (32d). Moreover, we identify and
discuss the indicators which have strong predictive power.Comment: ACM Multimedia 2014, November 3-7, 2014, Orlando, Florida, US
Estimate of CP Violation for the LBNE Project and $\delta_{CP}
Measurements of CP violation (CPV) and the basic parameter are
the goals of the LBNE Project, which is being planned. Using the expected
energy and baseline parameters for the LBNE Project, CPV and the dependence of
CPV on are estimated, to help in the planning of this project.Comment: 7 pages, 1 figur
Renormalization of Optical Excitations in Molecules near a Metal Surface
The lowest electronic excitations of benzene and a set of donor-acceptor
molecular complexes are calculated for the gas phase and on the Al(111) surface
using the many-body Bethe-Salpeter equation (BSE). The energy of the
charge-transfer excitations obtained for the gas phase complexes are found to
be around 10% lower than the experimental values. When the molecules are placed
outside the surface, the enhanced screening from the metal reduces the exciton
binding energies by several eVs and the transition energies by up to 1 eV
depending on the size of the transition-generated dipole. As a striking
consequence we find that close to the metal surface the optical gap of benzene
can exceed its quasiparticle gap. A classical image charge model for the
screened Coulomb interaction can account for all these effects which, on the
other hand, are completely missed by standard time-dependent density functional
theory.Comment: 4 pages, 3 figures; revised versio
New insights on the dense molecular gas in NGC253 as traced by HCN and HCO+
We have imaged the central ~1kpc of the circumnuclear starburst disk in the
galaxy NGC253 in the HCN(1-0), HCO+(1-0), and CO(1-0) transitions at 60pc
resolution using the Owens Valley Radio Observatory Millimeter-Wavelength Array
(OVRO). We have also obtained Atacama Pathfinder Experiment (APEX) observations
of the HCN(4-3) and the HCO+(4-3) lines of the starburst disk. We find that the
emission from the HCN(1-0) and HCO+(1-0) transitions, both indicators of dense
molecular gas, trace regions which are non-distinguishable within the
uncertainties of our observations. Even though the continuum flux varies by
more than a factor 10 across the starburst disk, the HCN/HCO+ ratio is constant
throughout the disk, and we derive an average ratio of 1.1+/-0.2. From an
excitation analysis we find that all lines from both molecules are subthermally
excited and that they are optically thick. This subthermal excitation implies
that the observed HCN/HCO+ line ratio is sensitive to the underlying chemistry.
The constant line ratio thus implies that there are no strong abundance
gradients across the starburst disk of NGC253. This finding may also explain
the variations in L'(HCN)/L'(HCO+) between different star forming galaxies both
nearby and at high redshifts.Comment: 9 pages, 12 figures, ApJ in press (volume 666 September
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