98 research outputs found

    Line identification studies using traditional techniques and wavelength coincidence statistics

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    Traditional line identification techniques result in the assignment of individual lines to an atomic or ionic species. These methods may be supplemented by wavelength coincidence statistics (WCS). The strength and weakness of these methods are discussed using spectra of a number of normal and peculiar B and A stars that have been studied independently by both methods. The present results support the overall findings of some earlier studies. WCS would be most useful in a first survey, before traditional methods have been applied. WCS can quickly make a global search for all species and in this way may enable identifications of an unexpected spectrum that could easily be omitted entirely from a traditional study. This is illustrated by O I. WCS is a subject to well known weakness of any statistical technique, for example, a predictable number of spurious results are to be expected. The danger of small number statistics are illustrated. WCS is at its best relative to traditional methods in finding a line-rich atomic species that is only weakly present in a complicated stellar spectrum

    Photographic region elemental abundance analyses of Dr. David S. Leckrone's GTO HST stars 2

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    Activities are presented for the grant-funded work at the Dominion Astrophysical (DAO) and Casleo Observatories. A comparison is planned for the spectrograms taken at both observatories of similar stars. It is reported that of the Northern Hemisphere program stars, only 112 Her remains to be analyzed. A preliminary solution for the components of this binary system has been found. The new ATLAS9 models have been used to reevaluate the effective temperatures and surface gravities derived for all program stars. Model atmospheres are being calculated by extensive grids on workstations upgraded to the DEC 3000 model 300X running Open VMS. An attached paper describes a plan to obtain the needed gf values as well as some first applications of astrophysical gf values, the most important of which was Vega

    A multiplet table for Mn I (Adelman, Svatek, Van Winkler, Warren 1989): Documentation for the machine-readable version

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    The machine-readable version of the multiplet table, as it is currently being distributed from the Astronomical Data Center, is described. The computerized version of the table contains data on excitation potentials, J values, multiplet terms, intensities of the transitions, and multiplet numbers. Files ordered by multiplet and by wavelength are included in the distributed version

    HD 35502: a hierarchical triple system with a magnetic B5IVpe primary

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    We present our analysis of HD~35502 based on high- and medium-resolution spectropolarimetric observations. Our results indicate that the magnetic B5IVsnp star is the primary component of a spectroscopic triple system and that it has an effective temperature of 18.4±0.6kK18.4\pm0.6\,{\rm kK}, a mass of 5.7±0.6M5.7\pm0.6\,M_\odot, and a polar radius of 3.00.5+1.1R3.0^{+1.1}_{-0.5}\,R_\odot. The two secondary components are found to be essentially identical A-type stars for which we derive effective temperatures (8.9±0.3kK8.9\pm0.3\,{\rm kK}), masses (2.1±0.2M2.1\pm0.2\,M_\odot), and radii (2.1±0.4R2.1\pm0.4\,R_\odot). We infer a hierarchical orbital configuration for the system in which the secondary components form a tight binary with an orbital period of 5.66866(6)d5.66866(6)\,{\rm d} that orbits the primary component with a period of over 40yrs40\,{\rm yrs}. Least-Squares Deconvolution (LSD) profiles reveal Zeeman signatures in Stokes VV indicative of a longitudinal magnetic field produced by the B star ranging from approximately 4-4 to 0kG0\,{\rm kG} with a median uncertainty of 0.4kG0.4\,{\rm kG}. These measurements, along with the line variability produced by strong emission in Hα\alpha, are used to derive a rotational period of 0.853807(3)d0.853807(3)\,{\rm d}. We find that the measured vsini=75±5kms1v\sin{i}=75\pm5\,{\rm km\,s}^{-1} of the B star then implies an inclination angle of the star's rotation axis to the line of sight of 2410+6°24^{+6}_{-10}\degree. Assuming the Oblique Rotator Model, we derive the magnetic field strength of the B star's dipolar component (143+9kG14^{+9}_{-3}\,{\rm kG}) and its obliquity (63±13°63\pm13\degree). Furthermore, we demonstrate that the calculated Alfv\'{e}n radius (416+17R41^{+17}_{-6}\,R_\ast) and Kepler radius (2.10.7+0.4R2.1^{+0.4}_{-0.7}\,R_\ast) place HD~35502's central B star well within the regime of centrifugal magnetosphere-hosting stars.Comment: 24 pages, 14 figures, Accepted for publication in MNRA

    Weather in stellar atmosphere: the dynamics of mercury clouds in alpha Andromedae

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    The formation of long-lasting structures at the surfaces of stars is commonly ascribed to the action of strong magnetic fields. This paradigm is supported by observations of evolving cool spots in the Sun and active late-type stars, and stationary chemical spots in the early-type magnetic stars. However, results of our seven-year monitoring of mercury spots in non-magnetic early-type star alpha Andromedae show that the picture of magnetically-driven structure formation is fundamentally incomplete. Using an indirect stellar surface mapping technique, we construct a series of 2-D images of starspots and discover a secular evolution of the mercury cloud cover in this star. This remarkable structure formation process, observed for the first time in any star, is plausibly attributed to a non-equilibrium, dynamical evolution of the heavy-element clouds created by atomic diffusion and may have the same underlying physics as the weather patterns on terrestrial and giant planets.Comment: 10 pages, 2 figures; to be published in Nature Physic

    El patrón comercial a finales del siglo XIX: Un análisis comparativo

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    Nuevos enfoques en la historia económica de España y de América Latina. Homenaje a Robert W. Fogel y Douglas C. North, Premios Nobel de Economía 1993Editada en la Universidad Carlos IIIEn este ensayo se contrasta para una muestra de 18 países hacia 1913 una versión estática de la teoría de Heckscher-Ohlin, en la formulación de Vanek. La conclusión alcanzada es que si bien el modelo de H-O con competencia perfecta no resulta plenamente explicativo para la segunda posguerra mundial, es muy adecuado, sin embargo, para los años finales del siglo XIX y primeros del siglo XX.This paper will focus on the question: ¿does the Heckscher-Ohlin theory adequately account for the major aspects of the trade pattern observed prior to WWI, or are there other influences that mattered? I conclude that although the perfect competition H-O model does not do all that well for the post-world War II period, it is perfectly adequate for the late nineteenth century, the period which motivated Eli F. Heckscher and Bertil Ohlin in the first place.Publicad
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