scholarly journals Fundamental Parameters and Models of Stellar Atmospheres

1985 ◽  
Vol 111 ◽  
pp. 303-329
Author(s):  
Bengt Gustafsson ◽  
Uffe Graae-Jørgensen
Keyword(s):  
Model Atmosphere ◽  
Stellar Atmospheres ◽  
Chemical Compositions ◽  
Fundamental Parameters ◽  
Different Types ◽  
Effective Temperatures

The use of photometric and spectroscopic criteria, calibrated by model-atmosphere calculations, for determining effective temperatures, surface gravities and chemical compositions of stars is illustrated and commented on. The accuracy that can be obtained today in such calibrations is discussed, as well as possible ways of improving this accuracy further for different types of stars.

scholarly journals Using the CIFIST grid of CO5BOLD 3D model atmospheres to study the effects of stellar granulation on photometric colours

2018 ◽  
Vol 613 ◽  
pp. A24 ◽  
Author(s):  
A. Kučinskas ◽  
J. Klevas ◽  
H.-G. Ludwig ◽  
P. Bonifacio ◽  
M. Steffen ◽  
...  
Keyword(s):  
Main Sequence ◽  
Broad Band ◽  
Stellar Atmospheres ◽  
Spectral Energy ◽  
Energy Distributions ◽  
Different Types ◽  
Convective Motions ◽  
Effective Temperatures ◽  
Red Giant ◽  
Colour Indices

Aims. We studied the influence of convection on the spectral energy distributions (SEDs), photometric magnitudes, and colour indices of different types of stars across the H–R diagram. Methods. The 3D hydrodynamical CO5BOLD, averaged ⟨3D⟩, and 1D hydrostatic LHD model atmospheres were used to compute SEDs of stars on the main sequence (MS), main sequence turn-off (TO), subgiant branch (SGB), and red giant branch (RGB), in each case at two different effective temperatures and two metallicities, [M∕H] = 0.0 and − 2.0. Using the obtained SEDs, we calculated photometric magnitudes and colour indices in the broad-band Johnson-Cousins UBVRI and 2MASS JHKs, and the medium-band Strömgren uvby photometric systems. Results. The 3D–1D differences in photometric magnitudes and colour indices are small in both photometric systems and typically do not exceed ± 0.03 mag. Only in the case of the coolest giants located on the upper RGB are the differences in the U and u bands able reach ≈−0.2 mag at [M∕H] = 0.0 and ≈−0.1 mag at [M∕H] = −2.0. Generally, the 3D–1D differences are largest in the blue-UV part of the spectrum and decrease towards longer wavelengths. They are also sensitive to the effective temperature and are significantly smaller in hotter stars. Metallicity also plays a role and leads to slightly larger 3D–1D differences at [M∕H] = 0.0. All these patterns are caused by a complex interplay between the radiation field, opacities, and horizontal temperature fluctuations that occur due to convective motions in stellar atmospheres. Although small, the 3D–1D differences in the magnitudes and colour indices are nevertheless comparable to or larger than typical photometric uncertainties and may therefore cause non-negligible systematic differences in the estimated effective temperatures.

scholarly journals Model atmospheres and spectral analyses of Wolf-Rayet stars

1995 ◽  
Vol 163 ◽  
pp. 105-115
Author(s):  
W.-R. Hamann
Keyword(s):  
Chemical Compositions ◽  
Vertical Strip ◽  
Hydrogen Burning ◽  
Spectral Analyses ◽  
Fundamental Parameters ◽  
Processed Material ◽  
Cno Cycle ◽  
Interesting Correlation ◽  
Effective Temperatures ◽  
Expanding Atmospheres

Stratified non-LTE models for expanding atmospheres have become available in the recent years. They are based on the idealized assumptions of spherical symmetry, stationarity and radiative equilibrium. The satisfactory agreement between calculated and observed Wolf-Rayet spectra suggests that this “standard model” is basically adequate for describing real WR atmospheres and hence can be applied for their quantitative spectral analyses. By the application of these models, the fundamental parameters have been determined meanwhile for the majority of the known Galactic WR stars. Most WN stars populate a vertical strip in the Hertzspung-Russell diagram at effective temperatures of ≈35 kK, the luminosities ranging from 104.5 to 105.9L⊙. Only three WN stars of earliest subtype, other early-type WN stars if they have strong lines, and the WC stars are hotter. The chemical compositions of the WR atmospheres correspond to nuclear-processed material (WN: hydrogen burning in the CNO cycle; WC: helium burning). Hydrogen is depleted but still detectable in the cooler members of the WN subclass. Quantitatively, the hydrogen abundances show an interesting correlation with the luminosity which can be compared with the predictions from evolutionary calculations.

The Current Status in the Modelling of Stellar Atmospheres

2003 ◽  
Vol 210 ◽  
pp. 3-18 ◽  
Author(s):  
Bengt Gustafsson
Keyword(s):  
Recent Progress ◽  
Classification Scheme ◽  
Model Atmosphere ◽  
Stellar Atmospheres ◽  
Current Status ◽  
Contemporary Research ◽  
Quality Classification ◽  
Different Types

The old question whether models of stellar atmospheres are wrong, adequate, or even overelaborated, is discussed with a number of examples from contemporary research as a background. A simple quality classification scheme for models of different types is presented. It is concluded that, in spite of rapid recent progress, we are far from having fully satisfactory theoretical representations of stellar atmospheres. Reasons for continuing the efforts to reach a higher degree of physical consistency in model atmosphere work are discussed.

scholarly journals Gravity and limb-darkening coefficients for compact stars: DA, DB, and DBA eclipsing white dwarfs

2020 ◽  
Vol 634 ◽  
pp. A93 ◽  
Author(s):  
A. Claret ◽  
E. Cukanovaite ◽  
K. Burdge ◽  
P.-E. Tremblay ◽  
S. Parsons ◽  
...  
Keyword(s):  
White Dwarfs ◽  
Least Squares Method ◽  
Stellar Atmospheres ◽  
Eclipsing Binaries ◽  
Compact Stars ◽  
Stellar Disk ◽  
Chemical Compositions ◽  
Specific Intensity ◽  
Effective Temperatures ◽  
Limb Darkening

Context. The distribution of the specific intensity over the stellar disk is an essential tool for modeling the light curves in eclipsing binaries, planetary transits, and stellar diameters through interferometric techniques, line profiles in rotating stars, gravitational microlensing, etc. However, the available theoretical calculations are mostly restricted to stars on the main sequence or the giant branch, and very few calculations are available for compact stars. Aims. The main objective of the present work is to extend these investigations by computing the gravity and limb-darkening coefficients for white dwarf atmosphere models with hydrogen, helium, or mixed compositions (types DA, DB, and DBA). Methods. We computed gravity and limb-darkening coefficients for DA, DB, and DBA white dwarfs atmosphere models, covering the transmission curves of the Sloan, UBVRI, Kepler, TESS, and Gaia photometric systems. Specific calculations for the HiPERCAM instrument were also carried out. For all calculations of the limb-darkening coefficients we used the least-squares method. Concerning the effects of tidal and rotational distortions, we also computed for the first time the gravity-darkening coefficients y(λ) for white dwarfs using the same models of stellar atmospheres as in the case of limb-darkening. A more general differential equation was introduced to derive these quantities, including the partial derivative (∂ln Io(λ)/∂ln g)Teff. Results. Six laws were adopted to describe the specific intensity distribution: linear, quadratic, square root, logarithmic, power-2, and a more general one with four coefficients. The computations are presented for the chemical compositions log[H/He] = −10.0 (DB), −2.0 (DBA) and He/H = 0 (DA), with log g varying between 5.0 and 9.5 and effective temperatures between 3750 and 100 000 K. For effective temperatures higher than 40 000 K, the models were also computed adopting nonlocal thermal equilibirum (DA). The adopted mixing-length parameters are ML2/α = 0.8 (DA case) and 1.25 (DB and DBA). The results are presented in the form of 112 tables. Additional calculations, such as for other photometric systems and/or different values of log[H/He], log g, and Teff can be performed upon request.

scholarly journals Influences of different curing methods on chemical compositions in different types of tobaccos

2021 ◽  
Vol 167 ◽  
pp. 113534
Author(s):  
Jie Chen ◽  
Yan Li ◽  
Xian He ◽  
Fangchan Jiao ◽  
Meiling Xu ◽  
...  
Keyword(s):  
Chemical Compositions ◽  
Different Types ◽  
Curing Methods

scholarly journals Using non-solar-scaled opacities to derive stellar parameters

2018 ◽  
Vol 620 ◽  
pp. A54 ◽  
Author(s):  
C. Saffe ◽  
M. Flores ◽  
P. Miquelarena ◽  
F. M. López ◽  
M. Jaque Arancibia ◽  
...  
Keyword(s):  
High Precision ◽  
Chemical Species ◽  
Model Atmosphere ◽  
Condensation Temperature ◽  
Spectroscopic Methods ◽  
Fundamental Parameters ◽  
Evolved Stars ◽  
Solar Type ◽  
Scaled Models ◽  
Previous Step

Aims. In an effort to improve spectroscopic methods of stellar parameters determination, we implemented non-solar-scaled opacities in a simultaneous derivation of fundamental parameters and abundances. We wanted to compare the results with the usual solar-scaled method using a sample of solar-type and evolved stars. Methods. We carried out a high-precision determination of stellar parameters and abundances by applying non-solar-scaled opacities and model atmospheres. Our sample is composed of 20 stars, including main sequence and evolved objects. The stellar parameters were determined by imposing ionization and excitation equilibrium of Fe lines, with an updated version of the FUNDPAR program, together with plane-parallel ATLAS12 model atmospheres and the MOOG code. Opacities for an arbitrary composition and vmicro were calculated through the opacity sampling (OS) method. We used solar-scaled models in the first step, and then continued the process, but scaled to the abundance values found in the previous step (i.e. non-solar-scaled). The process finishes when the stellar parameters of one step are the same as in the previous step, i.e. we use a doubly iterated method. Results. We obtained a small difference in stellar parameters derived with non-solar-scaled opacities compared to classical solar-scaled models. The differences in Teff, log g, and [Fe/H] amount to 26 K, 0.05 dex, and 0.020 dex for the stars in our sample. These differences can be considered the first estimation of the error due to the use of classical solar-scaled opacities to derive stellar parameters with solar-type and evolved stars. We note that some chemical species could also show an individual variation greater than those of the [Fe/H] (up to ~0.03 dex) and varying from one species to another, obtaining a chemical pattern difference between the two methods. This means that condensation temperature Tc trends could also present a variation. We include an example showing that using non-solar-scaled opacities, the solution found with the classical solar-scaled method indeed cannot always verify the excitation and ionization balance conditions required for a model atmosphere. We discuss in the text the significance of the differences obtained when using solar-scaled versus non-solar-scaled methods. Conclusions. We consider that the use of the non-solar-scaled opacities is not mandatory in every statistical study with large samples of stars. However, for those high-precision works whose results depend on the mutual comparison of different chemical species (such as the analysis of condensation temperature Tc trends), we consider its application to be worthwhile. To date, this is probably one of the most precise spectroscopic methods for stellar parameter derivation.

scholarly journals The Review of Chemistry, Pharmacology and Processing Method of Rhubarb (Rheum species)

2019 ◽  
Vol 8 ◽  
Author(s):  
Jingwen He ◽  
Liang Wang ◽  
Hongxing Guo ◽  
Hui Zhao ◽  
Jiachen Sun
Keyword(s):  
Blood Circulation ◽  
Processing Method ◽  
The Body ◽  
Chemical Compositions ◽  
Pharmacological Activities ◽  
Processing Methods ◽  
Traditional Medicines ◽  
Toxic Materials ◽  
Different Types ◽  
Body Cooling

Rhubarb is one of the Chinese traditional medicines. About ninety-four compounds with five different types of skeletons (anthraquinone, anthrones, stilbenes, flavonoids and acylglucosides) have been isolated from rhubarb so far. These constituents are effective in purgative, clearing heat-fire, removing toxic materials from the body, cooling blood and promoting blood circulation. Recent studies have shown that the appropriate processing methods may directly impact on its nutraceutical activities and chemical compositions. Here, we summarize the update progress in the chemical compositions, pharmacological activities and processing methods of rhubarb.

scholarly journals Synthesis of Classification Dispersion Spectra from Stellar Atmospheres Theory and from High Dispersion Spectra

1976 ◽  
Vol 72 ◽  
pp. 17-18
Author(s):  
A. W. Irwin ◽  
C. T. Bolton ◽  
R. F. Garrison
Keyword(s):  
Spectral Synthesis ◽  
Stellar Atmospheres ◽  
Oscillator Strengths ◽  
Continuum Models ◽  
High Dispersion ◽  
University Of Toronto ◽  
Spectrum Synthesis ◽  
Effective Temperatures ◽  
The University ◽  
Temperature Surface

The ATLAS programme has been corrected and modified for use at low effective temperatures. A grid of unblanketed model atmospheres has been generated for the region G5-K5, V-II. A spectrum synthesis programme has been written for the calculation of flux vs wavelength for selected regions of the spectrum. Temperature distributions from the grid of continuum models and from published blanketed models will be used along with published oscillator strengths as input data for the spectral synthesis programme.Spectrograms of MK standards have been taken at 12 Å mm−1 and 120 Å mm−1. The University of Toronto PDS microdensitometer system has been programmed to allow comparison between the synthesized spectra and the observed spectra to determine the effects of effective temperature, surface gravity, microturbulence, and abundance on classification criteria.

scholarly journals Size-segregated characteristics of organic carbon (OC), elemental carbon (EC) and organic matter in particulate matter (PM) emitted from different types of ships in China

2020 ◽  
Vol 20 (3) ◽  
pp. 1549-1564 ◽  
Author(s):  
Fan Zhang ◽  
Hai Guo ◽  
Yingjun Chen ◽  
Volker Matthias ◽  
Yan Zhang ◽  
...  
Keyword(s):  
Particle Size ◽  
Elemental Carbon ◽  
Fine Particles ◽  
Particle Mass ◽  
Fuel Oil ◽  
Chemical Compositions ◽  
Particle Sizes ◽  
Heavy Fuel Oil ◽  
Different Types ◽  
Marine Diesel

Abstract. Studies of detailed chemical compositions in particles with different size ranges emitted from ships are in serious shortage. In this study, size-segregated distributions and characteristics of particle mass, organic carbon (OC), elemental carbon (EC), 16 EPA polycyclic aromatic hydrocarbons (PAHs) and 25 n-alkanes measured aboard 12 different vessels in China are presented. The results showed the following. (1) More than half of the total particle mass, OC, EC, PAHs and n-alkanes were concentrated in fine particles with aerodynamic diameter (Dp) < 1.1 µm for most of the tested ships. The relative contributions of OC, EC, PAH and alkanes to the size-segregated particle mass are decreasing with the increase in particle size. However, different types of ships showed quite different particle-size-dependent chemical compositions. (2) In fine particles, the OC and EC were the dominant components, while in coarse particles, OC and EC only accounted for very small proportions. With the increase in particle size, the OC / EC ratios first decreased and then increased, having the lowest values for particle sizes between 0.43 and 1.1 µm. (3) Out of the four OC fragments and three EC fragments obtained in thermal–optical analysis, OC1, OC2 and OC3 were the dominant OC fragments for all the tested ships, while EC1 and EC2 were the main EC fragments for ships running on heavy fuel oil (HFO) and marine-diesel fuel, respectively; different OC and EC fragments presented different distributions in different particle sizes. (4) The four-stroke low-power diesel fishing boat (4-LDF) had much higher PAH emission ratios than the four-stroke high-power marine-diesel vessel (4-HMV) and two-stroke high-power heavy-fuel-oil vessel (2-HHV) in fine particles, and 2-HHV had the lowest values. (5) PAHs and n-alkanes showed different profile patterns for different types of ships and also between different particle-size bins, which meant that the particle size should be considered when source apportionment is conducted. It is also noteworthy from the results in this study that the smaller the particle size, the more toxic the particle was, especially for the fishing boats in China.

scholarly journals Stellar Atmospheres and Chemical Compositions of Galaxies

1980 ◽  
Vol 5 ◽  
pp. 811-815
Author(s):  
Lawrence H. Aller
Keyword(s):  
Los Angeles ◽  
Photon Counting ◽  
Stellar Atmospheres ◽  
Balmer Line ◽  
Chemical Compositions ◽  
Energy Distributions ◽  
Counting System ◽  
Theoretical Predictions ◽  
External Galaxies ◽  
The University

AbstractThe chemical compositions of external galaxies are usually found from their HII regions or composite absorption line spectra of their nuclei. In the Magellanic Clouds, however, individual stars are observable, but objects heretofore studied necessarily have been luminous la supergiants which border on the brink of instability. The image photon counting system on the Anglo-Australian Telescope makes it possible to observe fainter, more stable Ib supergiants. Energy distributions and Balmer line profiles for these stars can be fitted with theoretical predictions by Kurucz. A joint effort by J.E. Ross and B.J. O’Mara of the University of Queensland, Bruce Peterson of the Anglo-Australian Observatory, and a group at the University of California, Los Angeles to analyze three lb supergiants suggests that metals of the iron group are depleted by a factor of 2-3.5 with respect to the normal chemical composition of our own galaxy.

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