98 research outputs found
Line identification studies using traditional techniques and wavelength coincidence statistics
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
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
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
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 , a mass of
, and a polar radius of . The
two secondary components are found to be essentially identical A-type stars for
which we derive effective temperatures (), masses
(), and radii (). We infer a
hierarchical orbital configuration for the system in which the secondary
components form a tight binary with an orbital period of
that orbits the primary component with a period of over .
Least-Squares Deconvolution (LSD) profiles reveal Zeeman signatures in Stokes
indicative of a longitudinal magnetic field produced by the B star ranging
from approximately to with a median uncertainty of
. These measurements, along with the line variability produced
by strong emission in H, are used to derive a rotational period of
. We find that the measured of the B star then implies an inclination angle of the star's
rotation axis to the line of sight of . Assuming the
Oblique Rotator Model, we derive the magnetic field strength of the B star's
dipolar component () and its obliquity
(). Furthermore, we demonstrate that the calculated Alfv\'{e}n
radius () and Kepler radius
() 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
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
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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Photometric calibrations for 21st century science
The answers to fundamental science questions in astrophysics, ranging from the history of the expansion of the universe to the sizes of nearby stars, hinge on our ability to make precise measurements of diverse astronomical objects. As our knowledge of the underlying physics of objects improves along with advances in detectors and instrumentation, the limits on our capability to extract science from measurements is set, not by our lack of understanding of the nature of these objects, but rather by the most mundane of all issues: the precision with which we can calibrate observations in physical units. In principle, photometric calibration is a solved problem - laboratory reference standards such as blackbody furnaces achieve precisions well in excess of those needed for astrophysics. In practice, however, transferring the calibration from these laboratory standards to astronomical objects of interest is far from trivial - the transfer must reach outside the atmosphere, extend over 4{pi} steradians of sky, cover a wide range of wavelengths, and span an enormous dynamic range in intensity. Virtually all spectrophotometric observations today are calibrated against one or more stellar reference sources, such as Vega, which are themselves tied back to laboratory standards in a variety of ways. This system's accuracy is not uniform. Selected regions of the electromagnetic spectrum are calibrated extremely well, but discontinuities of a few percent still exist, e.g., between the optical and infrared. Independently, model stellar atmospheres are used to calibrate the spectra of selected white dwarf stars, e.g. the HST system, but the ultimate accuracy of this system should be verified against laboratory sources. Our traditional standard star systems, while sufficient until now, need to be improved and extended in order to serve future astrophysics experiments. This white paper calls for a program to improve upon and expand the current networks of spectrophotometrically calibrated stars to provide precise calibration with an accuracy of equal to and better than 1% in the ultraviolet, visible and near-infrared portions of the spectrum, with excellent sky coverage and large dynamic range
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