23,387 research outputs found
Chemical analysis of giant stars in the young open cluster NGC 3114
Context: Open clusters are very useful targets for examining possible trends
in galactocentric distance and age, especially when young and old open clusters
are compared. Aims: We carried out a detailed spectroscopic analysis to derive
the chemical composition of seven red giants in the young open cluster NGC
3114. Abundances of C, N, O, Li, Na, Mg, Al, Ca, Si, Ti, Ni, Cr, Y, Zr, La, Ce,
and Nd were obtained, as well as the carbon isotopic ratio. Methods: The
atmospheric parameters of the studied stars and their chemical abundances were
determined using high-resolution optical spectroscopy. We employed the
local-thermodynamic-equilibrium model atmospheres of Kurucz and the spectral
analysis code MOOG. The abundances of the light elements were derived using the
spectral synthesis technique. Results: We found that NGC 3114 has a mean
metallicity of [Fe/H] = -0.01+/-0.03. The isochrone fit yielded a turn-off mass
of 4.2 Msun. The [N/C] ratio is in good agreement with the models predicted by
first dredge-up. We found that two stars, HD 87479 and HD 304864, have high
rotational velocities of 15.0 km/s and 11.0 km/s; HD 87526 is a halo star and
is not a member of NGC 3114. Conclusions: The carbon and nitrogen abundance in
NGC 3114 agree with the field and cluster giants. The oxygen abundance in NGC
3114 is lower compared to the field giants. The [O/Fe] ratio is similar to the
giants in young clusters. We detected sodium enrichment in the analyzed cluster
giants. As far as the other elements are concerned, their [X/Fe] ratios follow
the same trend seen in giants with the same metallicity.Comment: 17 pages, 9 figures, 10 tables; accepted for publication in A&
Detection of new eruptions in the Magellanic Clouds LBVs R 40 and R 110
We performed a spectroscopic and photometric analysis to study new eruptions
in two luminous blue variables (LBVs) in the Magellanic Clouds. We detected a
strong new eruption in the LBV R40 that reached in 2016, which is
around mag brighter than the minimum registered in 1985. During this new
eruption, the star changed from an A-type to a late F-type spectrum. Based on
photometric and spectroscopic empirical calibrations and synthetic spectral
modeling, we determine that R\,40 reached ~K
during this new eruption. This object is thereby probably one of the coolest
identified LBVs. We could also identify an enrichment of nitrogen and r- and
s-process elements. We detected a weak eruption in the LBV R 110 with a maximum
of mag in 2011, that is, around mag brighter than in the
quiescent phase. On the other hand, this new eruption is about mag
fainter than the first eruption detected in 1990, but the temperature did not
decrease below 8500 K. Spitzer spectra show indications of cool dust in the
circumstellar environment of both stars, but no hot or warm dust was present,
except by the probable presence of PAHs in R\,110. We also discuss a possible
post-red supergiant nature for both stars
Chemical abundances and kinematics of barium stars
In this paper we present an homogeneous analysis of photospheric abundances
based on high-resolution spectroscopy of a sample of 182 barium stars and
candidates. We determined atmospheric parameters, spectroscopic distances,
stellar masses, ages, luminosities and scale height, radial velocities,
abundances of the Na, Al, -elements, iron-peak elements, and s-process
elements Y, Zr, La, Ce, and Nd. We employed the local-thermodynamic-equilibrium
model atmospheres of Kurucz and the spectral analysis code {\sc moog}. We found
that the metallicities, the temperatures and the surface gravities for barium
stars can not be represented by a single gaussian distribution. The abundances
of -elements and iron peak elements are similar to those of field giants
with the same metallicity. Sodium presents some degree of enrichment in more
evolved stars that could be attributed to the NeNa cycle. As expected, the
barium stars show overabundance of the elements created by the s-process. By
measuring the mean heavy-element abundance pattern as given by the ratio
[s/Fe], we found that the barium stars present several degrees of enrichment.
We also obtained the [hs/ls] ratio by measuring the photospheric abundances of
the Ba-peak and the Zr-peak elements. Our results indicated that the [s/Fe] and
the [hs/ls] ratios are strongly anti-correlated with the metallicity. Our
kinematical analysis showed that 90% of the barium stars belong to the thin
disk population. Based on their luminosities, none of the barium stars are
luminous enough to be an AGB star, nor to become self-enriched in the s-process
elements. Finally, we determined that the barium stars also follow an
age-metallicity relation.Comment: 30 pages, 26 figures, 18 tables, accepted for publication in MNRA
Gravitational Collapse of a Massless Scalar Field and a Perfect Fluid with Self-Similarity of the First Kind in (2+1) Dimensions
Self-similar solutions of a collapsing perfect fluid and a massless scalar
field with kinematic self-similarity of the first kind in 2+1 dimensions are
obtained. Their local and global properties of the solutions are studied. It is
found that some of them represent gravitational collapse, in which black holes
are always formed, and some may be interpreted as representing cosmological
models.Comment: 13 page
Photonic superdiffusive motion in resonance line radiation trapping - partial frequency redistribution effects
The relation between the jump length probability distribution function and
the spectral line profile in resonance atomic radiation trapping is considered
for Partial Frequency Redistribution (PFR) between absorbed and reemitted
radiation. The single line Opacity Distribution Function [M.N. Berberan-Santos
et.al. J.Chem.Phys. 125, 174308 (2006)] is generalized for PFR and used to
discuss several possible redistribution mechanisms (pure Doppler broadening,
combined natural and Doppler broadening and combined Doppler, natural and
collisional broadening). It is shown that there are two coexisting scales with
a different behavior: the small scale is controlled by the intricate PFR
details while the large scale is essentially given by the atom rest frame
redistribution asymptotic. The pure Doppler and combined natural, Doppler and
collisional broadening are characterized by both small and large scale
superdiffusive Levy flight behaviors while the combined natural and Doppler
case has an anomalous small scale behavior but a diffusive large scale
asymptotic. The common practice of assuming complete redistribution in core
radiation and frequency coherence in the wings of the spectral distribution is
incompatible with the breakdown of superdiffusion in combined natural and
Doppler broadening conditions
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