601 research outputs found
Calibrating the Cepheid Period-Luminosity relation with the VLTI
The VLTI is the ideal instrument for measuring the distances of nearby
Cepheids with the Baade-Wesselink method, allowing an accurate recalibration of
the Cepheid Period-Luminosity relation. The high accuracy required by such
measurement, however, can only be reached taking into account the effects of
limb darkening, and its dependence on the Cepheid pulsations. We present here
our new method to compute phase- and wavelength-dependent limb darkening
profiles, based on hydrodynamic simulation of Classical Cepheid atmospheres.Comment: 3 pages, 2 postscript figures, uses eas.cls LaTeX class file, to
appear in the proc. Eurowinter School "Observing with the VLTI", Feb 3-8
2002, Les Houches (France
Magnetic circular dichroism in X-ray fluorescence of Heusler alloys at threshold excitation
The results of fluorescence measurements of magnetic circular dichroism (MCD)
in Mn L_2,L_3 X-ray emission and absorption for Heusler alloys NiMnSb and
Co2MnSb are presented. Very intense resonance Mn L_3 emission is found at the
Mn 2p_3/2 threshold and is attributed to a peculiarity of the threshold
excitation in materials with the half-metallic character of the electronic
structure. A theoretical model for the description of resonance scattering of
polarized x-rays is suggested.Comment: 3 pages, 2 figures. Discussed at conferences, submitting process in
progres
Doping Dependent Changes in Nitrogen 2 States in the Diluted Magnetic Semiconductor GaCrN
We study the electronic structure of the recently discovered diluted magnetic
semiconductor GaCrN ( = 0.01-0.10). A systematic study of the
changes in the and ligand (N) partial density of states
(DOS) of the host lattice is carried out using N 1 soft x-ray emission and
absorption spectroscopy, respectively. X-ray absorption measurements confirm
the wurtzite N 2 DOS and substitutional doping of Cr into Ga-sites. Coupled
changes in the and N 2 character DOS of
GaCrN identify states responsible for ferromagnetism consistent
with band structure calculations.Comment: 5 pages, 4 figures, submitted to Phys. Rev.
Improved Baade-Wesselink surface-brightness relations
Recent, and older accurate, data on (limb-darkened) angular diameters is
compiled for 221 stars, as well as BVRIJK[12][25] magnitudes for those objects,
when available. Nine stars (all M-giants or supergiants) showing excess in the
[12-25] colour are excluded in the analysis as this may indicate the present of
dust influencing the optical and near-infrared colours as well. Based on this
large sample, Baade-Wesselink surface-brightness (SB) relations are presented
for dwarfs, giants, supergiants and dwarfs in the optical and near-infrared.
M-giants are found to follow different SB-relations from non-M giants, in
particular in V-(V-R). The preferred relation for non-M giants are compared to
earlier relation by Fouque & Gieren (1997, based on 10 stars) and Nordgren et
al. (2002, based on 57 stars). Increasing the sample size does not lead to a
lower rms value. It is shown that the residuals do not correlate with
metallicity at a significant level. The finally adopted observed angular
diameters are compared to those predicted by Cohen et al. (1999) for 45 stars
in common, and there is reasonable overall, to good agreement when \theta <6
mas. Finally, I comment on the common practice in the literature to average,
and then fix, the zero point of the V-(V-K), V-(V-R) and K-(J-K) relations, and
then re-derive the slopes. Such a common zero point at zero colour is not
expected from model atmospheres for the (V-R) colour and depends on gravity.
Relations derived in this way may be biased.Comment: accepted for publication in the MNRA
Electronic structure investigation of CoO by means of soft X-ray scattering
The electronic structure of CoO is studied by resonant inelastic soft X-ray
scattering spectroscopy using photon energies across the Co 2p absorption
edges. The different spectral contributions from the energy-loss structures are
identified as Raman scattering due to d-d and charge-transfer excitations. For
excitation energies close to the L3 resonance, the spectral features are
dominated by quartet-quartet and quartet-doublet transitions of the 3d7
configuration. At excitation energies corresponding to the satellites in the Co
2p X-ray absorption spectrum of CoO, the emission features are instead
dominated by charge-transfer transitions to the 3d8L-1 final state. The spectra
are interpreted and discussed with the support of simulations within the single
impurity Anderson model with full multiplet effects which are found to yield
consistent spectral functions to the experimental data.Comment: 8 pages, 2 figures, 2 tables,
http://link.aps.org/doi/10.1103/PhysRevB.65.20510
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