875 research outputs found
Relation between the phenomenological interactions of the algebraic cluster model and the effective two--nucleon forces
We determine the phenomenological cluster--cluster interactions of the
algebraic model corresponding to the most often used effective two--nucleon
forces for the O + system.Comment: Latex with Revtex, 1 figure available on reques
Medium-resolution echelle spectroscopy of pulsating variables and exoplanet host stars with sub-meter telescopes
Here we present two of our interesting results obtained over the last 18
months from spectroscopic monitoring of binary pulsating stars and exoplanet
host stars. Our investigations are very promising by demonstrating that modern
fiber-fed spectrographs open a whole new chapter in the life of small national
and university observatories.Comment: 3 pages, 3 figures. To be published in the proceedings of the
workshop on "Observing techniques, instrumentation and science for
metre-class telescopes", Sep. 2013, Tatranska Lomnica, Slovaki
Discovery of the spectroscopic binary nature of the classical Cepheids FN Aql and V1344 Aql
We present the analysis of photometric and spectroscopic data of two
classical Cepheids, FN Aquilae and V1344 Aquilae. Based on the joint treatment
of the new and earlier radial velocity data, both Galactic Cepheids have been
found to be a member in a spectroscopic binary system.
To match the phases of the earlier radial velocity data correctly with the
new ones, we also determined the temporal behaviour of the pulsation period of
these Cepheids based on all available photometric data. The O-C graph covering
about half century shows slight changes in the pulsation period due to stellar
evolution for both Cepheids.Comment: 7 pages, 6 figures, 7 tables, accepted for publishing in the MNRA
The s process in AGB stars as constrained by a large sample of barium stars
© ESO 2018. Context. Barium (Ba) stars are dwarf and giant stars enriched in elements heavier than iron produced by the slow neutron-capture process (s process). These stars belong to binary systems in which the primary star evolved through the asymptotic giant branch (AGB) phase. During this phase the primary star produced s-process elements and transferred them onto the secondary, which is now observed as a Ba star. Aims. We compare the largest homogeneous set of Ba giant star observations of the s-process elements Y, Zr, La, Ce, and Nd with AGB nucleosynthesis models to reach a better understanding of the s process in AGB stars. Methods. By considering the light-s (ls: Y and Zr) heavy-s (hs: La, Ce, and Nd) and elements individually, we computed for the first time quantitative error bars for the different hs-element to ls-element abundance ratios, and for each of the sample stars. We compared these ratios to low-mass AGB nucleosynthesis models. We excluded La from our analysis because the strong La lines in some of the sample stars cause an overestimation and unreliable abundance determination, as compared to the other observed hs-Type elements. Results. All the computed hs-Type to ls-Type element ratios show a clear trend of increasing with decreasing metallicity with a small spread (less than a factor of 3). This trend is predicted by low-mass AGB models in which 13C is the main neutron source. The comparison with rotating AGB models indicates the need for the presence of an angular momentum transport mechanism that should not transport chemical species, but significantly reduces the rotational speed of the core in the advanced stellar evolutionary stages. This is an independent confirmation of asteroseismology observations of the slow down of core rotation in giant stars, and of rotational velocities of white dwarfs lower than predicted by models without an extra angular momentum transport mechanism
Barium stars as tracers of s-process nucleosynthesis in AGB stars II. Using machine learning techniques on 169 stars
We aim to analyse the abundance pattern of 169 Barium (Ba) stars, using
machine learning techniques and the AGB final surface abundances predicted by
Fruity and Monash stellar models. We developed machine learning algorithms that
use the abundance pattern of Ba stars as input to classify the initial mass and
metallicity of its companion star using stellar model predictions. We use two
algorithms: the first exploits neural networks to recognise patterns and the
second is a nearest-neighbour algorithm, which focuses on finding the AGB model
that predicts final surface abundances closest to the observed Ba star values.
In the second algorithm we include the error bars and observational
uncertainties to find the best fit model. The classification process is based
on the abundances of Fe, Rb, Sr, Zr, Ru, Nd, Ce, Sm, and Eu. We selected these
elements by systematically removing s-process elements from our AGB model
abundance distributions, and identifying those whose removal has the biggest
positive effect on the classification. We excluded Nb, Y, Mo, and La. Our final
classification combines the output of both algorithms to identify for each Ba
star companion an initial mass and metallicity range. With our analysis tools
we identify the main properties for 166 of the 169 Ba stars in the stellar
sample. The classifications based on both stellar sets of AGB final abundances
show similar distributions, with an average initial mass of M = 2.23 MSun and
2.34 MSun and an average [Fe/H] = -0.21 and -0.11, respectively. We
investigated why the removal of Nb, Y, Mo, and La improves our classification
and identified 43 stars for which the exclusion had the biggest effect. We show
that these stars have statistically significant different abundances for these
elements compared to the other Ba stars in our sample. We discuss the possible
reasons for these differences in the abundance patterns.Comment: accepted for publication in A&
Graduate HRD Programs in South Korea
The Problem To address national issues associated with societal development, many countries are recognizing the need to educate individuals who will lead developmental initiatives. While many previous studies have been conducted to examine how and what content of human resource development (HRD) has been taught in Western countries, similar research efforts have been rarely conducted in Asian countries such as South Korea. The lack of comparative study creates a research gap in understanding how HRD programs have been designed and implemented in different countries.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline
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