322 research outputs found
The effect of continuum scattering processes on spectral line formation
The effect of scattering processes in the continuum on the formation of
spectral lines in a static atmosphere with an arbitrary distribution of the
internal energy sources is investigated using Ambartsumian's principle of
invariance. Spectral line profiles are calculated to illustrate the effect the
assumption of the complete redistribution on atoms and coherent scattering in
continuum may have on the emergent intensity. The one-dimensional case is
considered for simplicity.Comment: 11 pages (including 2 figures). Accepted for publication in Journ. of
Quant. Spectr. and Rad. Transfe
Abundances in Damped Ly-alpha Galaxies
Damped Ly_alpha galaxies provide a sample of young galaxies where chemical
abundances can be derived throughout the whole universe with an accuracy
comparable to that for the local universe. Despite a large spread in redshift,
HI column density and metallicity, DLA galaxies show a remarkable uniformity in
the elemental ratios rather suggestive of similar chemical evolution if not of
an unique population. These galaxies are characterized by a moderate, if any,
enhancement of alpha-elements over Fe-peak elemental abundance with [S/Zn]
about 0 and [O/Zn] about 0.2, rather similarly to the dwarfs galaxies in the
Local Group. Nitrogen shows a peculiar behaviour with a bimodal distribution
and possibly two plateaux. In particular, the plateau at low N abundances
([N/H] < -3), is not observed in other atrophysical sites and might be evidence
for primary N production by massive stars.Comment: To appear in the Proceedings of the ESO/Arcetri Workshop on "Chemical
Abundances and Mixing in Stars in the Milky Way and its Satellites", eds., L.
Pasquini and S. Randich (Springer-Verlag Series, "ESO Astrophysics Symposia"
Abundance ratios of volatile vs. refractory elements in planet-harbouring stars: hints of pollution?
We present the [X/H] trends as function of the elemental condensation
temperature Tc in 88 planet host stars and in a volume-limited comparison
sample of 33 dwarfs without detected planetary companions. We gathered
homogeneous abundance results for many volatile and refractory elements
spanning a wide range of Tc, from a few dozens to several hundreds kelvin. We
investigate possible anomalous trends of planet hosts with respect to
comparison sample stars in order to detect evidence of possible pollution
events. No significant differences are found in the behaviour of stars with and
without planets. This result is in agreement with a ``primordial'' origin of
the metal excess in planet host stars. However, a subgroup of 5 planet host and
1 comparison sample stars stands out for having particularly high [X/H] vs. Tc
slopes.Comment: 10 pages, 7 figures, accepted for publication in A&A. Figures with
higher resolution are available at www.iac.es/proyect/abuntes
ARES v2 - new features and improved performance
Aims: We present a new upgraded version of ARES. The new version includes a
series of interesting new features such as automatic radial velocity
correction, a fully automatic continuum determination, and an estimation of the
errors for the equivalent widths. Methods: The automatic correction of the
radial velocity is achieved with a simple cross-correlation function, and the
automatic continuum determination, as well as the estimation of the errors,
relies on a new approach to evaluating the spectral noise at the continuum
level. Results: ARES v2 is totally compatible with its predecessor. We show
that the fully automatic continuum determination is consistent with the
previous methods applied for this task. It also presents a significant
improvement on its performance thanks to the implementation of a parallel
computation using the OpenMP library.Comment: 4 pages, 2 Figures; accepted in A&A; ARES Webpage:
www.astro.up.pt/~sousasag/are
On the functional form of the metallicity-giant planet correlation
It is generally accepted that the presence of a giant planet is strongly
dependent on the stellar metallicity. A stellar mass dependence has also been
investigated, but this dependence does not seem as strong as the metallicity
dependence. Even for metallicity, however, the exact form of the correlation
has not been established. In this paper, we test several scenarios for
describing the frequency of giant planets as a function of its host parameters.
We perform this test on two volume-limited samples (from CORALIE and HARPS). By
using a Bayesian analysis, we quantitatively compared the different scenarios.
We confirm that giant planet frequency is indeed a function of metallicity.
However, there is no statistical difference between a constant or an
exponential function for stars with subsolar metallicities contrary to what has
been previously stated in the literature. The dependence on stellar mass could
neither be confirmed nor be discarded.Comment: 5 pages, 2 figures, accepted in A&
Higher depletion of lithium in planet host stars: no age and mass effect
Recent observational work by Israelian et al. has shown that sun-like planet
host stars in the temperature range 5700K < Teff < 5850K have lithium
abundances that are significantly lower than those observed for "single" field
stars. In this letter we use stellar evolutionary models to show that
differences in stellar mass and age are not responsible for the observed
correlation. This result, along with the finding of Israelian et al., strongly
suggest that the observed lithium difference is likely linked to some process
related to the formation and evolution of planetary systems.Comment: 4 pages, 4 figures, letter accepted for publication in Astronomy &
Astrophysic
Properties of the PCygni wind found using the Self Absorption Curve method
We have used the optical lines of N II and Fe III to study the wind of the
luminous blue variable P Cyg. This was performed by applying a version of the
Self Absorption Curve (SAC) method, involving few assumptions, to lines whose
flux can be measured. A rather surprising result was obtained; the lines of
more excited multiplets without blue shifted absorption components appear to be
optically thick, while the lines of the most excited multiplets may show some
indications of being optically thicker than the lines of less excited ones.
Explanations of such effects are discussed, including possible inhomogeneities
in the wind.Comment: accepted by Astronomy & Astrophysic
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