10,260 research outputs found
3D molecular line formation in dwarf carbon-enhanced metal-poor stars
We present a detailed analysis of the carbon and nitrogen abundances of two
dwarf carbon-enhanced metal-poor (CEMP) stars: SDSS J1349-0229 and SDSS
J0912+0216. We also report the oxygen abundance of SDSS J1349-0229. These stars
are metal-poor, with [Fe/H] < -2.5, and were selected from our ongoing survey
of extremely metal-poor dwarf candidates from the Sloan Digital SkySurvey
(SDSS). The carbon, nitrogen and oxygen abundances rely on molecular lines
which form in the outer layers of the stellar atmosphere. It is known that
convection in metal-poor stars induces very low temperatures which are not
predicted by `classical' 1D stellar atmospheres. To obtain the correct
temperature structure, one needs full 3D hydrodynamical models. Using CO5BOLD
3D hydrodynamical model atmospheres and the Linfor3D line formation code,
molecular lines of CH, NH, OH and C2 were computed, and 3D carbon, nitrogen and
oxygen abundances were determined. The resulting carbon abundances were
compared to abundances derived using atomic CI lines in 1D LTE and NLTE. There
is not a good agreement between the carbon abundances determined from C2 bands
and from the CH band, and molecular lines do not agree with the atomic CI
lines. Although this may be partly due to uncertainties in the transition
probabilities of the molecular bands it certainly has to do with the
temperature structure of the outer layers of the adopted model atmosphere. We
explore the influence of the 3D model properties on the molecular abundance
determination. In particular, the choice of the number of opacity bins used in
the model calculations and its subsequent effects on the temperature structure
and molecular line formation is discussed. (Abridged)Comment: Poster presented at IAU JD 10, Rio de Janeiro, 10-11 August 2009,
published in Memorie della Societa' Astronomica Italiana, Vol. 80 n.3 P.735.
One reference corrected, matches the published versio
Solar analogs with and without planets: T trends and galactic evolution
We explore a sample of 148 solar-like stars to search for a possible
correlation between the slopes of the abundance trends versus condensation
temperature (known as the Tc slope) both with stellar parameters and Galactic
orbital parameters in order to understand the nature of the peculiar chemical
signatures of these stars and the possible connection with planet formation. We
find that the Tc slope correlates at a significant level with the stellar age
and the stellar surface gravity. We also find tentative evidence that the Tc
slope correlates with the mean galactocentric distance of the stars (Rmean),
suggesting that stars that originated in the inner Galaxy have fewer refractory
elements relative to the volatile ones. We found that the chemical
peculiarities (small refractory-to-volatile ratio) of planet-hosting stars is
probably a reflection of their older age and their inner Galaxy origin. We
conclude that the stellar age and probably Galactic birth place are key to
establish the abundances of some specific elements.Comment: Proceedings of the GREAT-ITN conference: The Milky Way Unravelled by
Gaia. Will be published in the "EAS Publications Series
Sex prediction by metric and non-metric analysis of the hard palate and the pyriform aperture
Background: Analysis of the bones and bone fragments of the cranium may be a useful tool for sex diagnosis in the identification of human remains which have been exposed to adverse conditions. The object of the present study was to evaluate sex prediction through metric and non-metric analysis of the hard palate (HP) and the pyriform aperture (PA), using macerated skulls of adult individuals.Â
Materials and methods: We analysed 312 dry skulls of adult individuals of both sexes, studying the metric and non-metric characteristics of the HP and PA. The accuracy, sensitivity, specificity and positive and negative predictive values were evaluated. A binary logistic regression and a linear regression were performed. The receiver operating characteristic curve was constructed to analyse the perfor- mance of sex diagnosis. Measurements of the HP and the PA were analysed by ANOVA and Tukey’s test. The SPSS v. 20.0 software was used, with a significance threshold of 5%.Â
Results: The shape of the PA presented 61.9% accuracy, 54.4% sensitivity and 65.7% specificity. The shape of the HP presented 51.5% accuracy, 65.6% sen- sitivity and 44.7% specificity. Only the height of the PA functioned as a good predictor of sex.Â
Conclusions: The height of the PA produced good diagnostic performance (area under curve = 0.764). The height of the PA was the most reliable indicator for sex prediction, and could be used by forensic scientists to identify sex.
Proper motions of the HH1 jet
We describe a new method for determining proper motions of extended objects,
and a pipeline developed for the application of this method. We then apply this
method to an analysis of four epochs of [S~II] HST images of the HH~1 jet
(covering a period of ~yr).
We determine the proper motions of the knots along the jet, and make a
reconstruction of the past ejection velocity time-variability (assuming
ballistic knot motions). This reconstruction shows an "acceleration" of the
ejection velocities of the jet knots, with higher velocities at more recent
times. This acceleration will result in an eventual merging of the knots in
~yr and at a distance of from the outflow source, close to
the present-day position of HH~1.Comment: 12 pages, 8 figure
The Pristine survey II: a sample of bright stars observed with FEROS
Extremely metal-poor (EMP) stars are old objects formed in the first Gyr of
the Universe. They are rare and, to select them, the most successful strategy
has been to build on large and low-resolution spectroscopic surveys. The
combination of narrow- and broad band photometry provides a powerful and
cheaper alternative to select metal-poor stars. The on-going Pristine Survey is
adopting this strategy, conducting photometry with the CFHT MegaCam wide field
imager and a narrow-band filter centred at 395.2 nm on the CaII-H and -K lines.
In this paper we present the results of the spectroscopic follow-up conducted
on a sample of 26 stars at the bright end of the magnitude range of the Survey
(g<=15), using FEROS at the MPG/ESO 2.2 m telescope. From our chemical
investigation on the sample, we conclude that this magnitude range is too
bright to use the SDSS gri bands, which are typically saturated. Instead the
Pristine photometry can be usefully combined with the APASS gri photometry to
provide reliable metallicity estimates.Comment: AN accepte
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