601 research outputs found
Backus-Gilbert footprint matching methodology applied on MWI and ICI observations
Final report of the EUMETSAT study with contract number EUM/CO/18/4600002075/CJA
Employees of Greatness: Signifying Values in Performance Appraisal Criteria
The spread of performance-based and variable pay systems has affected expectations on employee contributions and remuneration, which have become increasingly personalized and individualized. Based on a theoretical valuation studies approach, this study of performance-based pay systems in Sweden shows that performance appraisals are (e)valuations of employees’ yearly performance in which they are prized and (ap)praised at the same time. Through a document analysis of performance criteria from four organizations, the study analyzes how values expressed refer to Boltanski and Thévenot’s six orders of worth. The analysis resulted in a theoretical construction of a joint ideal of Employees of Greatness, against which employees are measured and remunerated. The existence of the ideal of employee greatness is explained by the increasing congruence of organizational ideals in private and public sectors, as principles from emotional and cognitive forms of capitalist organization are superimposed on traditional industrial capitalist organizational ideals
A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
We have constructed a grid of about 10,000 spherically symmetric and
plane-parallel models with the MARCS program, and make it available for public
use. Parameter ranges are: Teff=2500 to 8000 K, log g =log(GM/R2)= -1 to 5
(cgs) with various masses and radii, [Me/H]=-5 to +1, with [Alpha/Fe] = 0.0 and
0.4 and different choices of C and N abundances to also represent stars of
types R, S and N, and with microturbulence parameters from 1 to 5 km/s. We also
list fluxes in approximately 108,000 wavelength points. Underlying assumptions
in addition to 1D stratification include hydrostatic equilibrium, MLT
convection and LTE. A number of general properties of the models are discussed,
in relation to the effects of changing blanketing and sphericity.
Models are compared with other available grids and excellent agreement is
found with plane-parallel models of Castelli and Kurucz within the overlapping
parameter range. Although there are departures from the spherically symmetric
NextGen models, the agreement with more recent PHOENIX models is gratifying.
The models of the grid show regularities, but some interesting departures from
general patterns occur for the coolest models due to the molecular opacities.
We have tested rules of thumb concerning effects of blanketing and sphericity
and found them to often be astonishingly accurate. Some interesting new
phenomena have been discovered, such as the intricate coupling between
blanketing and sphericity, and the strong effects of carbon enhancement on
metal-poor models. We give further details of models and comparisons with
observations in subsequent papers.Comment: 20 pages, 20 figures, to be published in Astronomy & Astrophysic
Line-blanketed model atmospheres for R Coronae Borealis stars and hydrogen-deficient carbon stars
We have constructed line-blanketed model atmospheres for the hydrogen-deficient and carbon-rich R Coronae Borealis (RCrB) stars, as well as for the similar hydrogen-deficient carbon (HdC) stars and the cool extreme helium (EHe) stars. Improved continuum opacities have been used together with realistic line absorption data for atomic and molecular transitions. The observed dereddened fluxes of R CrB are compared with the calculated model fluxes and found to agree best with a model effective temperature of 6900K, while the infrared flux method gives between 6600 and 6900K, depending on the nature of the flux excess in the J and H bands compared to the model fluxes. The excess may correspond to a recently formed dust cloud close to the star, with a typical temperature around 2000K and a dust mass of ~10^-11^M_{sun}_. The agreement for the ultraviolet flux distribution is also very satisfactory as seen from IUE spectra of RCrB. Theoretical broad band photometry is presented and effective temperatures of RCrB and HdC stars estimated. The constructed models show a significantly steeper temperature gradient compared to previously existing models as a result of the line opacity. Due to the cool surface and high abundance of carbon, molecular bands of e.g. C_2_ and CO are visible in the spectra even at as high effective temperatures as 7000K. Furthermore, the high temperatures encountered at depth explain the observed Hei and CII lines for T_eff_ down to ~7000K. In the inner layers ({tau}_Ross_ > 3) the models show density inversions related to the ionization zone of helium. For certain low gravity models the luminosity exceeds the local Eddington limit and hence gas pressure inversions occur as well, which could be related to the decline events of RCrB stars
A Constraint on Z_\odot from Fits of Isochrones to the Color-Magnitude Diagram of M67
The mass at which a transition is made between stars that have radiative or
convective cores throughout the core H-burning phase is a fairly sensitive
function of Z (particularly the CNO abundances). As a consequence, the ~4 Gyr,
open cluster M67 provides a constraint on Z_\odot (and the solar heavy-element
mixture) because (i) high-resolution spectroscopy indicates that this system
has virtually the same metal abundances as the Sun, and (ii) its turnoff stars
have masses just above the lower limit for sustained core convection on the
main sequence. In this study, evolutionary tracks and isochrones using the
latest MARCS model atmospheres as boundary conditions have been computed for
0.6-1.4 solar masses on the assumption of a metals mix (implying Z_\odot =
0.0125) based on the solar abundances derived by M. Asplund and collaborators
using 3-D model atmospheres. These calculations do not predict a turnoff gap
where one is observed in M67. No such difficulty is found if the analysis uses
isochrones for Z_\odot = 0.0165, assuming the Grevesse & Sauval (1998) mix of
heavy elements. Our findings, like the inferences from helioseismology,
indicate a problem with the Asplund et al. abundances. However, it is possible
that low-Z models with diffusive processes taken into account will be less
problematic.Comment: 13 pages, including 2 figures and 1 table; accepted (July 2007) for
publication in the Astrophysical Journal Letter
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