Chiapas, Mexico

2010 essay contest winner Linnaea Cunha\u27s Chiapas, Mexic

Can we trust elemental abundances derived in late-type giants with the classical 1D stellar atmosphere models?

We compare the abundances of various chemical species as derived with 3D hydrodynamical and classical 1D stellar atmosphere codes in a late-type giant characterized by T_eff=3640K, log g = 1.0, [M/H] = 0.0. For this particular set of atmospheric parameters the 3D-1D abundance differences are generally small for neutral atoms and molecules but they may reach up to 0.3-0.4 dex in case of ions. The 3D-1D differences generally become increasingly more negative at higher excitation potentials and are typically largest in the optical wavelength range. Their sign can be both positive and negative, and depends on the excitation potential and wavelength of a given spectral line. While our results obtained with this particular late-type giant model suggest that 1D stellar atmosphere models may be safe to use with neutral atoms and molecules, care should be taken if they are exploited with ions.Comment: Poster presented at the IAU Symposium 265 "Chemical Abundances in the Universe: Connecting First Stars to Planets", Rio de Janeiro, 10-14 August 2009; 2 pages, 1 figur

A view of the Galactic halo using beryllium as a time scale

Beryllium stellar abundances were suggested to be a good tracer of time in the early Galaxy. In an investigation of its use as a cosmochronometer, using a large sample of local halo and thick-disk dwarfs, evidence was found that in a log(Be/H) vs. [alpha/Fe] diagram the halo stars separate into two components. One is consistent with predictions of evolutionary models while the other is chemically indistinguishable from the thick-disk stars. This is interpreted as a difference in the star formation history of the two components and suggests that the local halo is not a single uniform population where a clear age-metallicity relation can be defined.Comment: To appear in Proceedings of the International Astronomical Union, IAU Symposium, Volume 265, Chemical abundances in the Universe: connecting first stars to planets, K. Cunha, M. Spite and B. Barbuy, eds. 2 Pages, 2 figure

Comments on "Casimir Effect in the Kerr spacetime with Quintessence"

This comment is devoted to the recalculation of the Casimir energy of a massless scalar field in the Kerr black hole surrounded by quintessence derived in [B. Toshmatov, Z. Stuchl\'{i}k and B. Ahmedov, Eur. Phys. J. Plus {\bf 132}, 98 (2017)] and its comparison with the results recently obtained in [V. B. Bezerra, M. S. Cunha, L. F. F. Freitas and C. R. Muniz, Mod. Phys. Lett. A {\bf 32}, 1750005 (2017)] in the spacetime [S. G. Ghosh, Eur. Phys. J. C {\bf 76}, 222 (2016)]. We have shown that in the more realistic spacetime which does not have the failures illustrated here, the Casimir energy is significantly bigger than that derived in [V. B. Bezerra, M. S. Cunha, L. F. F. Freitas and C. R. Muniz, Mod. Phys. Lett. A {\bf 32}, 1750005 (2017)], and the difference becomes crucial especially in the regions of near horizons of the spacetime.Comment: 6 pages, 2 figure

Liquids-Rich Shale Evaluation: Modelling and Optimization of Hydraulically Fractured Liquids-Rich Shale Wells

Imperial Users onl

Solar abundances and 3D model atmospheres

We present solar photospheric abundances for 12 elements from optical and near-infrared spectroscopy. The abundance analysis was conducted employing 3D hydrodynamical (CO5BOLD) as well as standard 1D hydrostatic model atmospheres. We compare our results to others with emphasis on discrepancies and still lingering problems, in particular exemplified by the pivotal abundance of oxygen. We argue that the thermal structure of the lower solar photosphere is very well represented by our 3D model. We obtain an excellent match of the observed center-to-limb variation of the line-blanketed continuum intensity, also at wavelengths shortward of the Balmer jump.Comment: Contributed paper, to be published in the proceedings of IAU Symposium 265, eds. K. Cunha, M. Spite, and B. Barbuy, Cambridge University Press (CUP). 2 figures, 4 page

Chromosome numbers of Angiosperms from the Juan Fernández Islands, the Tristan da Cunha Archipelago, and from Mainland Chile

Chromosome counts for eight native species in six genera from Juan Fernández Islands, five native species in three genera from Tristan da Cunha, and three species in two genera from mainland Chile are presented and discussed. They include the only chromosome number reports for angiosperms from Tristan da Cunha and first counts for the endemics Robinsonia thurifera and Wahlenbergia larrainii ( Juan Fernández), Agrostis carmichaelii, Acaena sarmentosa, A. stangii, and Nertera holmboei (Tristan da Cunha), and for Galium araucanum and Ourisia coccinea from Chile. Counts for Eryngium bupleuroides and Galium hypocarpium differ from earlier published reports