21,383 research outputs found
Stellar indices and kinematics in Seyfert 1 nuclei
We present spectra of 6 type 1 Seyfert galaxies, 2 Seyfert 2, a starburst
galaxy and a compact narrow line radiogalaxy, taken in two spectral ranges
centered around the near--IR CaII triplet (CaT) (at ~8600 Angstroms), and the
Mgb stellar feature at 5180 Angstroms. We measured the equivalent width (EWs)
of these features and the Fe52 and Fe53 spectral indices. We found that the
strength of the CaT in type 1 Seyfert galaxies with prominent central point
sources, is larger than what would be expected from the observed strength of
the blue indices. This could be explained by the presence of red supergiants in
the nuclei of Seyfert 1 galaxies. On the other hand, the blue indices of these
galaxies could also be diluted by the strong FeII multiplets that can be seen
in their spectra.
We have also measured the stellar and gas velocity dispersions of the
galaxies in the sample. The stellar velocity dispersions were measured using
both, the Mgb and CaT stellar features. The velocity dispersion of the gas in
the narrow line region (NLR) was measured using the strong emission lines
[OIII] 5007, 4959 and [SIII] 9069. We compare the gas and star velocity
dispersions and find that both magnitudes are correlated in Seyfert galaxies.
Most of the Seyfert 1 we observe have stellar velocity dispersion somehow
greater than that of the gas in the NLR.Comment: To appear in MNRAS, 18 pages, 9 figure
How does breakup influence the total fusion of Li at the Coulomb barrier?
Total (complete + incomplete) fusion excitation functions of Li on
Co and Bi targets around the Coulomb barrier are obtained using
a new continuum discretized coupled channel (CDCC) method of calculating
fusion. The relative importance of breakup and bound-state structure effects on
total fusion is particularly investigated. The effect of breakup on fusion can
be observed in the total fusion excitation function. The breakup enhances the
total fusion at energies just around the barrier, whereas it hardly affects the
total fusion at energies well above the barrier. The difference between the
experimental total fusion cross sections for Li on Co is notably
caused by breakup, but this is not the case for the Bi target.Comment: 9 pages, 9 figures, Submitted to Phys. Rev.
Correlations between reflected and transmitted intensity patterns emerging from opaque disordered media
The propagation of monochromatic light through a scattering medium produces
speckle patterns in reflection and transmission, and the apparent randomness of
these patterns prevents direct imaging through thick turbid media. Yet, since
elastic multiple scattering is fundamentally a linear and deterministic
process, information is not lost but distributed among many degrees of freedom
that can be resolved and manipulated. Here we demonstrate experimentally that
the reflected and transmitted speckle patterns are correlated, even for opaque
media with thickness much larger than the transport mean free path, proving
that information survives the multiple scattering process and can be recovered.
The existence of mutual information between the two sides of a scattering
medium opens up new possibilities for the control of transmitted light without
any feedback from the target side, but using only information gathered from the
reflected speckle.Comment: 6 pages, 4 figure
High velocity blue-shifted FeII absorption in the dwarf star-forming galaxy PHL293B: Evidence for a wind driven supershell?
X-shooter and ISIS WHT spectra of the starforming galaxy PHL 293B also known
as A2228-00 and SDSS J223036.79-000636.9 are presented in this paper.
We find broad (FWHM = 1000km/s) and very broad (FWZI = 4000km/s) components
in the Balmer lines, narrow absorption components in the Balmer series
blueshifted by 800km/s, previously undetected FeII multiplet (42) absorptions
also blueshifted by 800km/s, IR CaII triplet stellar absorptions consistent
with [Fe/H] < -2.0 and no broad components or blushifted absorptions in the HeI
lines. Based on historical records, we found no optical variability at the 5
sigma level of 0.02 mag between 2005 and 2013 and no optical variability at the
level of 0.1mag for the past 24 years.
The lack of variability rules out transient phenomena like luminous blue
variables or SN IIn as the origin of the blue shifted absorptions of HI and
FeII. The evidence points to either a young and dense expanding supershell or a
stationary cooling wind, in both cases driven by the young cluster wind.Comment: Accepted for publication in MNRAS; 15 pages, 10 figure
The role of gas infall in the evolution of disc galaxies
Spiral galaxies are thought to acquire their gas through a protracted infall phase resulting in the inside-out growth of their associated discs. For field spirals, this infall occurs in the lower density environments of the cosmic web. The overall infall rate, as well as the galactocentric radius at which this infall is incorporated into the star-forming disc, plays a pivotal role in shaping the characteristics observed today. Indeed, characterising the functional form of this spatio-temporal infall in-situ is exceedingly difficult, and one is forced to constrain these forms using the present day state of galaxies with model or simulation predictions. We present the infall rates used as input to a grid of chemical evolution models spanning the mass spectrum of discs observed today. We provide a systematic comparison with alternate analytical infall schemes in the literature, including a first comparison with cosmological simulations. Identifying the degeneracies associated with the adopted infall rate prescriptions in galaxy models is an important step in the development of a consistent picture of disc galaxy formation and evolution
Surface abundances of ON stars
Massive stars burn hydrogen through the CNO cycle during most of their
evolution. When mixing is efficient, or when mass transfer in binary systems
happens, chemically processed material is observed at the surface of O and B
stars. ON stars show stronger lines of nitrogen than morphologically normal
counterparts. Whether this corresponds to the presence of material processed
through the CNO cycle or not is not known. Our goal is to answer this question.
We perform a spectroscopic analysis of a sample of ON stars with atmosphere
models. We determine the fundamental parameters as well as the He, C, N, and O
surface abundances. We also measure the projected rotational velocities. We
compare the properties of the ON stars to those of normal O stars. We show that
ON stars are usually helium-rich. Their CNO surface abundances are fully
consistent with predictions of nucleosynthesis. ON stars are more chemically
evolved and rotate - on average - faster than normal O stars. Evolutionary
models including rotation cannot account for the extreme enrichment observed
among ON main sequence stars. Some ON stars are members of binary systems, but
others are single stars as indicated by stable radial velocities. Hence, mass
transfer is not a simple explanation for the observed chemical properties. We
conclude that ON stars show extreme chemical enrichment at their surface,
consistent with nucleosynthesis through the CNO cycle. Its origin is not clear
at present.Comment: 18 pages, 10 figures (+ appendix). A&A accepte
Integral Equation Analysis of Plane Wave Scattering by Coplanar Graphene-Strip Gratings in the THz Range
The plane wave scattering and absorption by finite and infinite gratings of
free-space standing infinitely long graphene strips are studied in the THz
range. A novel numerical approach, based on graphene surface impedance,
hyper-singular integral equations, and the Nystrom method, is proposed. This
technique guarantees fast convergence and controlled accuracy of computations.
Reflectance, transmittance, and absorbance are carefully studied as a function
of graphene and grating parameters, revealing the presence of surface plasmon
resonances. Specifically, larger graphene relaxation times increases the number
of resonances in the THz range, leading to higher wave transmittance due to the
reduced losses; on the other hand an increase of graphene chemical potential
up-shifts the frequency of plasmon resonances. It is also shown that a
relatively low number of graphene strips (>10) are able to reproduce Rayleigh
anomalies. These features make graphene strips good candidates for many
applications, including tunable absorbers and frequency selective surfaces.Comment: 11 pages, 26 figure
Magnetic properties of Co doped Nb clusters
From magnetic deflection experiments on isolated Co doped Nb clusters we made
the interesting observation of some clusters being magnetic, while others
appear to be non-magnetic. There are in principle two explanations for this
behavior. Either the local moment at the Co site is completely quenched or it
is screened by the delocalized electrons of the cluster, i.e. the Kondo effect.
In order to reveal the physical origin, we conducted a combined theoretical and
experimental investigation. First, we established the ground state geometry of
the clusters by comparing the experimental vibrational spectra with those
obtained from a density functional theory study. Then, we performed an analyses
based on the Anderson impurity model. It appears that the non-magnetic clusters
are due to a complete quenching of the local Co moment and not due to the Kondo
effect. In addition, the magnetic behavior of the clusters can be understood
from an inspection of their electronic structure. Here magnetism is favored
when the effective hybridization around the chemical potential is small, while
the absence of magnetism is signalled by a large effective hybridization around
the chemical potential.Comment: 14 pages, 8 figure
Relating breakup and incomplete fusion of weakly-bound nuclei through a classical trajectory model with stochastic breakup
A classical dynamical model that treats break-up stochastically is presented
for low energy reactions of weakly-bound nuclei. The three-dimensional model
allows a consistent calculation of breakup, incomplete and complete fusion
cross sections. The model is assessed by comparing the breakup observables with
CDCC quantum mechanical predictions, which are found to be in reasonable
agreement. Through the model, it is demonstrated that the breakup probability
of the projectile as a function of its distance from the target is of primary
importance for understanding complete and incomplete fusion at energies near
the Coulomb barrier.Comment: Accepted in Physical Review Letter
- âŠ