scholarly journals Temperatura efectiva en estrellas de tipo solar

2019 ◽  
pp. 81-86
Keyword(s):  
Quantum Theory ◽  
Space Physics ◽  
Stellar Atmospheres ◽  
Line Profiles ◽  
Carnegie Institution ◽  
Santa Barbara ◽  
University Of Texas ◽  
Spectral Profiles ◽  
Solar Type ◽  
The University

Temperatura efectiva en estrellas de tipo solar D. Cornejo, I. Ramírez, P. Barklem, W. Guevara Dirección de Astrofísica, Comisión Nacional de Investigación y Desarrollo Aeroespacial - CONIDA, Luis Felipe Villarán 1069, San Isidro, Lima, Perú. The Observatories of the Carnegie Institution for Science; 813 Santa Barbara Street, Pasadena, CA 91101, USA. Department of Astronomy and Space Physics, Uppsala University, Box 515, 751-20 Uppsala, Sweden DOI: https://doi.org/10.33017/RevECIPeru2011.0027/ RESUMEN Este trabajo consiste en determinar la temperatura efectiva de una muestra de 62 estrellas de tipo solar mediante el método de ajuste de perfiles teóricos a la linea espectral Hα (6562.8 A). Las estrellas analizadas han sido observadas usando el Telescopio Harlan J. Smith de 2.7 m del Observatorio McDonald de la Universidad de Texas mientras que los perfiles teóricos se basan en modelos de atmósferas estelares y teoría cuántica mas recientes. Nuestros resultados poseen un margen de error interno de ≈ 20 K, lo cual nos permite comparar nuestras temperaturas con aquellas determinadas usando otros métodos y especular sobre el origen de las diferencias observadas. Descriptores: Perfiles de lineas espectrales, atmósferas estelares. ABSTRACT The effective temperature for a sample of 62 solar-type stars has been determined fitting theoretical spectral profiles to observed Hα lines (6562.8 A). The stars analyzed has been observed using the 2.7 m Harlan J. Smith telescope at the McDonald Observatory of the University of Texas. The theoretical profiles are based on recent models of stellar atmospheres and quantum theory. The calculated temperatures have internal errors of ≈ 20 K with other techniques and speculate about the origin of the observed differences. Keywords: Spectral line profiles, Stellar Atmospheres.

scholarly journals Non-Local Convection Models for Stellar Atmospheres and Envelopes

2003 ◽  
Vol 210 ◽  
pp. 143-156
Author(s):  
F. Kupka
Keyword(s):  
Numerical Simulations ◽  
Main Sequence ◽  
Stellar Atmospheres ◽  
Surface Velocity ◽  
Line Profiles ◽  
Main Sequence Stars ◽  
Solar Type ◽  
Non Local ◽  
Stress Models ◽  
Do So

We present an overview of the concepts underlying advanced non-local Reynolds stress models of turbulent convection and review a comparison of this approach with a series of numerical simulations of fully compressible convection. We then discuss results from applications of the model to complete envelopes of A-type main sequence stars. The non-local model reproduces surface velocities in agreement with the lower limit of observed macro- and microturbulence velocities of A-star photospheres, the asymmetry of the surface velocity field as inferred from spectral line profiles, and the overall structure of the photospheric and subphotospheric convection zones, as predicted by the most recent numerical simulations available for these stars. Traditionally, local models of convection are unable to do so. We conclude with a brief survey of extensions of the model which are interesting for other applications such as atmospheres of solar type stars and overshooting below deep convective envelopes or above the core in massive stars.

scholarly journals Paso del Norte

2010 ◽  
Vol 1 (2) ◽  
Author(s):  
Carlos Morton
Keyword(s):  
San Francisco ◽  
Political Theatre ◽  
Santa Barbara ◽  
Political Issues ◽  
University Of Texas ◽  
Latino People ◽  
Paso Del Norte ◽  
The 1960S ◽  
The Many ◽  
The University

 Carlos Morton is a leading Chicano dramatist, who has been writing and producing  plays for more than four decades. Among his best-known plays are The Many Deaths of Danny Rosales (1983) and Johnny Tenorio (1992). In addition to his work for the stage, which has been widely produced, he has written for television and radio, and taught at universities in Texas, California, and Mexico (he holds a PhD from the University of Texas, Austin). When he started his career, at the end of the 1960s and the start of the 1970s, his enthusiasm was sparked by the political theatre produced by Teatro Campesino and the San Francisco Mime Troupe.  His work has since adopted a wider variety of styles and themes:  evoking historical events, myths, biblical stories, and contemporary political issues, such as racism and machismo, interweaving realism with fantasy. But he always addresses a Chicano audience, and exposes the oppression of Chicano and Latino people.  He is currently Professor of Theater at the University of California at Santa Barbara. 

scholarly journals 3D non-LTE corrections for Li abundance and 6Li/7Li isotopic ratio in solar-type stars

2018 ◽  
Vol 618 ◽  
pp. A16 ◽  
Author(s):  
G. Harutyunyan ◽  
M. Steffen ◽  
A. Mott ◽  
E. Caffau ◽  
G. Israelian ◽  
...  
Keyword(s):  
Spectral Synthesis ◽  
Isotopic Ratio ◽  
Stellar Atmospheres ◽  
Line Profiles ◽  
Solar Mass ◽  
Lithium Abundance ◽  
Dwarf Stars ◽  
Link Type ◽  
Solar Type ◽  
The Impact

Context. Convective motions in solar-type stellar atmospheres induce Doppler shifts that affect the strengths and shapes of spectral absorption lines and create slightly asymmetric line profiles. One-dimensional (1D) local thermodynamic equilibrium (LTE) studies of elemental abundances are not able to reproduce this phenomenon, which becomes particularly important when modeling the impact of isotopic fine structure, like the subtle depression created by the 6Li isotope on the red wing of the Li I resonance doublet line. Aims. The purpose of this work is to provide corrections for the lithium abundance, A(Li), and the 6Li/7Li isotopic ratio that can easily be applied to correct 1D LTE lithium abundances in G and F dwarf stars of approximately solar mass and metallicity for three-dimensional (3D) and non-LTE (NLTE) effects. Methods. The corrections for A(Li) and 6Li/7Li are computed using grids of 3D NLTE and 1D LTE synthetic lithium line profiles, generated from 3D hydro-dynamical CO5BOLD and 1D hydrostatic model atmospheres, respectively. For comparative purposes, all calculations are performed for three different line lists representing the Li I λ670.8 nm spectral region. The 3D NLTE corrections are then approximated by analytical expressions as a function of the stellar parameters (Teff, log ℊ, [Fe/H], ν sin i, A(Li), 6Li/7Li). These are applied to adjust the 1D LTE isotopic lithium abundances in two solar-type stars, HD 207129 and HD 95456, for which high-quality HARPS observations are available. Results. The derived 3D NLTE corrections range between −0.01 and +0.11 dex for A(Li), and between −4.9 and −0.4% for 6Li/7Li, depending on the adopted stellar parameters. We confirm that the inferred 6Li abundance depends critically on the strength of the Si I 670.8025 nm line. Our findings show a general consistency with recent works on lithium abundance corrections. After the application of such corrections, we do not find a significant amount of 6Li in any of the two target stars. Conclusions. In the case of 6Li/7Li, our corrections are always negative, showing that 1D LTE analysis can significantly overestimate the presence of 6Li (up to 4.9% points) in the atmospheres of solar-like dwarf stars. These results emphasize the importance of reliable 3D model atmospheres combined with NLTE line formation for deriving precise isotopic lithium abundances. Although 3D NLTE spectral synthesis implies an extensive computational effort, the results can be made accessible with parametric tools like the ones presented in this work.

Construction of Single Stereocenters

2015 ◽  
Author(s):  
Tristan H. Lambert
Keyword(s):  
Medical Center ◽  
Columbia University ◽  
Santa Barbara ◽  
Electrophilic Amination ◽  
Ene Reaction ◽  
University Of Texas ◽  
University Of Wisconsin ◽  
Nucleophilic Displacement ◽  
Institute Of Technology ◽  
The University

James L. Leighton at Columbia University reported (Nature 2012, 487, 86) that the commercially available allylsilane 2 allylated acetoacetone (1) to furnish the enantioenriched tertiary carbinol 3. Alexander T. Radosevich demonstrated (Angew. Chem. Int. Ed. 2012, 51, 10605) that diazaphospholidine 5 induced the formal reductive insertion of 3,5-dinitrobenzoic acid to α-ketoester 4 to generate adduct 6 enantioselectively. Tehshik P. Yoon at the University of Wisconsin at Madison found (J. Am Chem. Soc. 2012, 134, 12370) that aminoalcohol derivative 9 could be prepared via an asymmetric iron-catalyzed oxyamination of diene 7 using oxaziridine 8. A procedure for the desymmetrization of 1,3-difluoropropanol 10 by nucleophilic displacement of an unactivated aliphatic fluoride to generate 11 was reported (Angew. Chem. Int. Ed. 2012, 51, 12275) by Günter Haufe at the University of Münster and Norio Shibata at the Nagoya Institute of Technology. An innovative procedure for the amination of unactivated olefins involving an ene reaction/[ 2,3]-rearrangement sequence (e.g., 12 to 13) was developed (J. Am. Chem. Soc. 2012, 134, 18495) by Uttam K. Tambar at the University of Texas Southwestern Medical Center. James P. Morken at Boston College demonstrated the stereospecific amination of borane 14 with methoxylamine to produce 15. The conversion of β-ketoester 16 to 18 by amination with 17 under oxidative conditions was reported (J. Am. Chem. Soc. 2012, 134, 18948) by Javier Read de Alaniz at the University of California at Santa Barbara. The electrophilic amination of silyl ketene acetal 19 with a functionalized hydroxylamine reagent to produce 20 was disclosed (Angew. Chem. Int. Ed. 2012, 51, 11827) by Koji Hirano and Masahiro Miura at Osaka University. Erick M. Carreira at ETH Zürich developed (Angew. Chem. Int. Ed. 2012, 51, 8652) the enantioconvergent thioetherification of alcohol 21 to produce 23 with high branched to linear selectivity and ee. The asymmetric conjugate addition of 2-aminothiophenol 25 to 24 catalyzed by mesitylcopper in the presence of ligand 26 was developed (Angew. Chem. Int. Ed. 2012, 51, 8551) by Naoya Kumagai and Masakatsu Shibasaki at the Institute of Microbial Chemistry in Tokyo. The enantioselective conversion of aldehyde 28 to α-fluoride 30 under catalysis by NHC 29 was developed (Angew. Chem. Int. Ed. 2012, 51, 10359) by Zhenyang Lin and Jianwei Sun at the Hong Kong University of Science and Technology.

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