scholarly journals Effective temperatures of red giants in the APOKASC catalogue and the mixing length calibration in stellar models

2018 ◽  
Vol 612 ◽  
pp. A68 ◽  
Author(s):  
M. Salaris ◽  
S. Cassisi ◽  
R. P. Schiavon ◽  
A. Pietrinferni
Keyword(s):  
Chemical Composition ◽  
Boundary Conditions ◽  
Effective Temperature ◽  
Outer Boundary ◽  
Stellar Model ◽  
Red Giants ◽  
Mixing Length ◽  
Important Conclusion ◽  
Model Calculations ◽  
Stellar Models

Red giants in the updated APOGEE-Kepler catalogue, with estimates of mass, chemical composition, surface gravity and effective temperature, have recently challenged stellar models computed under the standard assumption of solar calibrated mixing length. In this work, we critically reanalyse this sample of red giants, adopting our own stellar model calculations. Contrary to previous results, we find that the disagreement between the Teff scale of red giants and models with solar calibrated mixing length disappears when considering our models and the APOGEE-Kepler stars with scaled solar metal distribution. However, a discrepancy shows up when α-enhanced stars are included in the sample. We have found that assuming mass, chemical composition and effective temperature scale of the APOGEE-Kepler catalogue, stellar models generally underpredict the change of temperature of red giants caused by α-element enhancements at fixed [Fe/H]. A second important conclusion is that the choice of the outer boundary conditions employed in model calculations is critical. Effective temperature differences (metallicity dependent) between models with solar calibrated mixing length and observations appear for some choices of the boundary conditions, but this is not a general result.

scholarly journals Accurate Masses and Radii as Test Data for Stellar Models: Status and Progress on the Copenhagen Project

1993 ◽  
Vol 137 ◽  
pp. 361-363 ◽  
Author(s):  
J. Andersen ◽  
J.V. Clausen ◽  
B.E. Helt ◽  
K.T. Johansen ◽  
B. Nordström ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Test Data ◽  
Effective Temperature ◽  
Stellar Model ◽  
The Other ◽  
Important Ingredient ◽  
Stellar Models ◽  
Test Objects ◽  
Important Test

The most important ingredient of a stellar model is its initial mass. Hence, real stars with known masses are important test objects for stellar models. Initial chemical composition is the other important starting parameter and should therefore also be known (Clausen, 1992). Finally, the most direct indicator of the evolution of a star is its radius. Together, these parameters determine the effective temperature and luminosity of the model, to be tested against a real star.

scholarly journals Tests of Evolution Models Using Eclipsing Binaries

1995 ◽  
Vol 10 ◽  
pp. 419-422
Author(s):  
J. Andersen
Keyword(s):  
Chemical Composition ◽  
Star Clusters ◽  
Stellar Model ◽  
Eclipsing Binaries ◽  
Fundamental Parameter ◽  
Fundamental Parameters ◽  
Stellar Models ◽  
Absolute Age ◽  
Cluster Sequence ◽  
Hr Diagram

Stellar models are the means by which we describe and understand the distribution of stars in the HR diagram. A stellar model is, in principle, completely specified by the three fundamental parameters mass, chemical composition, and age. Comparing the properties of models and real stars with the same parameters will tell us if our recipe for constructing stellar models is realistic. Unfortunately, the only star for which all three are known independently of stellar models is the Sun. For stars of other masses and ages we must devise observational tests in which at least one fundamental parameter is unknown. Two such popular test objects are double-lined eclipsing binaries and star clusters.In suitable eclipsing binaries we can determine both masses and chemical composition; the absolute age is unknown, but the same for both stars. Since evolution depends most sensitively on the mass, eclipsing binaries provide a very direct test of the models, but only for two points on a single isochrone. In star clusters, neither ages nor individual masses are known, but the detailed shape and population of a well-observed cluster sequence in the HR diagram provide a number of additional probes into the models.

scholarly journals A systematic study of stellar models for C/O-rich Wolf-Rayet Stars

1988 ◽  
Vol 108 ◽  
pp. 92-91
Author(s):  
N. Langer ◽  
M. Kiriakidis
Keyword(s):  
Chemical Composition ◽  
Systematic Study ◽  
Effective Temperature ◽  
Mass Range ◽  
Stellar Mass ◽  
Stellar Structure ◽  
Chemical Compositions ◽  
Helium Stars ◽  
Pure Helium ◽  
Stellar Models

A grid of homogeneous stellar models for Wolf-Rayet stars in the mass range from 1 to 60 M⊙ has been computed. For each stellar mass, stars with eight different sets of chemical compositions — from pure helium stars with (Y,C,O)=(1,0,0) to extreme helium poor stars with (Y,C,O)=(0.02,0.11,0.87) — have been calculated in order to investigate the dependence of the stellar structure on the stellar mass and chemical composition. Modern input physics adapted to the exotic chemical composition of the Wolf-Rayet stars has been incorporated in the models, including effects of partial recombination of helium, carbon, and oxygen, and detailed opacity tables for 20 different combinations of the (Y,C,O)-abundances. Furthermore, we estimated the effect of the intense, partly optically thick Wolf-Rayet winds on their apparent effective temperature, using the formalism of de Loore et al. (1982, IAU-Symp. 99, 53) with the parameters: = 3 . 10−5M⊙yr−1, β = 2, and v∞ = 2000 km s−1.

scholarly journals A general confrontation between solar data and solar models

1996 ◽  
Vol 176 ◽  
pp. 527-538
Author(s):  
R. A. Bell ◽  
M. J. Tripicco
Keyword(s):  
Chemical Composition ◽  
Effective Temperature ◽  
Solar Model ◽  
Data Sets ◽  
The Sun ◽  
Model Calculations ◽  
Calculated Line ◽  
Cool Stars ◽  
Temperature Surface

Since its effective temperature, surface gravity and chemical composition are well established, the Sun has often been used for tests of model stellar photospheres. There are two important potential tests – firstly, comparisons of observed and calculated line spectra and, secondly, comparisons of observed and calculated fluxes. If solar model calculations can successfully reproduce both of these data sets, then it gives confidence in the quality of models of other cool stars. However, different observations of solar fluxes do not agree with one another with the precision required in testing solar models.

scholarly journals Mixing-length calibration from field stars

2019 ◽  
Vol 623 ◽  
pp. A59 ◽  
Author(s):  
G. Valle ◽  
M. Dell’Omodarme ◽  
P. G. Prada Moroni ◽  
S. Degl’Innocenti
Keyword(s):  
Heavy Element ◽  
Outer Boundary ◽  
Enrichment Ratio ◽  
Mixing Length ◽  
Random Errors ◽  
Perfect Agreement ◽  
Increasing Trend ◽  
Stellar Models ◽  
The Impact ◽  
The Ideal

Aims. We critically analysed the theoretical foundation and statistical reliability of the mixing-length calibration by means of standard (Teff, [Fe/H]) and global asteroseismic observables (Δν, νmax) of field stars. We also discussed the soundness of inferring a possible metallicity dependence of the mixing-length parameter from field stars. Methods. We followed a theoretical approach based on mock datasets of artificial stars sampled from a grid of stellar models with a fixed mixing-length parameter αml. We then recovered the mixing-length parameter of the mock stars by means of SCEPtER maximum-likelihood algorithm. We finally analysed the differences between the true and recovered mixing-length values quantifying the random errors due to the observational uncertainties and the biases due to possible discrepancies in the chemical composition and input physics between artificial stars and the models adopted in the recovery. Results. We verified that the αml estimates are affected by a huge spread, even in the ideal configuration of perfect agreement between the mock data and the recovery grid of models. While the artificial stars were computed at fixed solar-calibrated αml = 2.10, the recovered values had a mean of 2.20 and a standard deviation of 0.52. Then we explored the case in which the solar heavy-element mixture used to compute the models is different from that adopted in the artificial stars. We found an estimated mixing-length mean of 2.24 ± 0.48 and, more interestingly, a metallicity relationship in which αml increases by 0.4 for an increase of 1 dex in [Fe/H]. Thus, a simple heavy-element mixture mismatch induced a spurious, but statistically robust, dependence of the estimated mixing-length on metallicity. The origin of this trend was further investigated considering the differences in the initial helium abundance Y – [Fe/H] – initial metallicity Z relation assumed in the models and data. We found that a discrepancy between the adopted helium-to-metal enrichment ratio ΔY/ΔZ caused the appearance of spurious trends in the estimated mixing-length values. An underestimation of its value from ΔY/ΔZ = 2.0 in the mock data to ΔY/ΔZ = 1.0 in the recovery grid resulted in an increasing trend, while the opposite behaviour occurred for an equivalent overestimation. A similar effect was caused by an offset in the [Fe/H] to global metallicity Z conversion. A systematic overestimation of [Fe/H] by 0.1 dex in the recovery grid of models forced an increasing trend of αml versus [Fe/H] of about 0.2 per dex. We also explored the impact of some possible discrepancies between the adopted input physics in the recovery grid of models and mock data. We observed an induced trend with metallicity of about Δαml = 0.3 per dex when the effect of the microscopic diffusion is neglected in the recovery grid, while no trends originated from a wrong assumption on the effective temperature scale by ±100 K. Finally, we proved that the impact of different assumptions on the outer boundary conditions was apparent only in the RGB phase. Conclusions. We showed that the mixing-length estimates of field stars are affected by a huge spread even in an ideal case in which the stellar models used to estimate αml are exactly the same models as used to build the mock dataset. Moreover, we proved that there are many assumptions adopted in the stellar models used in the calibration that can induce spurious trend of the estimated αml with [Fe/H]. Therefore, any attempt to calibrate the mixing-length parameter by means of Teff, [Fe/H], Δν, and νmax of field stars seems to be statistically poorly reliable. As such, any claim about the possible dependence of the mixing-length on the metallicity for field stars should be considered cautiously and critically.

Study on the Military Environmental Information Management with GIS

2010 ◽  
Vol 113-116 ◽  
pp. 561-564
Author(s):  
Jian Ding ◽  
Ke Hong Wu ◽  
Zhi Bing Ding
Keyword(s):  
Decision Making ◽  
Information Management ◽  
Transportation Planning ◽  
Vital Role ◽  
Environmental Information ◽  
Gis Technology ◽  
Important Conclusion ◽  
Model Calculations ◽  
Hazardous Chemical ◽  
Application Fields

The application of GIS technology to Military Environmental Information(MEI) management will play a vital role in MEI management, and can lead to better decision-making. This paper discusses both the management method and the application fields. Case studies, like information management, pollution coverage evaluating, military transportation planning and monitoring, and decision-making supporting, are presented in this paper. Detailed digital basemap database, Digital Elevation Model(DEM) data, Digital OrthoImage Model(DOM) data, image database of Remote Sensing, Social economic element database, and other informations related to military features, can be integrated into MEI GIS, and will meet the needs for later query and statistics. Spatial analysis is the bridge that links fundamental data models to GIS technology. While buffer analysis can be used for identifying the locations of hazardous chemical storage sites in relation to residents living area, and can facilitate the evaluation of the threatened area in the event of a leak or spill of hazardous materials. Network analysis can be used in military transportation planning and monitoring. GIS is particularly useful in providing composite visual representation of fairly complex underlying model calculations, analysts can draw implicit and important conclusion from the already known geographical data. The study shows that the management of MEI using GIS technology is reasonable and feasible, and GIS is a highly efficient tool in MEI management.

Investigation of heat transfer in irregular porous cavity subjected to various boundary conditions

2019 ◽  
Vol 29 (1) ◽  
pp. 418-447 ◽  
Author(s):  
Irfan Anjum Badruddin
Keyword(s):  
Heat Transfer ◽  
Boundary Conditions ◽  
Outer Boundary ◽  
Governing Equations ◽  
Content Type ◽  
Porous Cavity ◽  
Various Boundary Conditions ◽  
Heating Source ◽  
Transfer Behavior ◽  
Vertical Walls

Purpose The purpose of this paper is to investigate the heat transfer in an arbitrary cavity filled with porous medium. The geometry of the cavity is such that an isothermal heating source is placed centrally at the bottom of the cavity. The height and width of the heating source is varied to analyses its effect on the heat transfer characteristics. The investigation is carried out for three different cases of outer boundary conditions such as two outside vertical walls being maintained at cold temperature To, two vertical and top horizontal surface being heated to. To and the third case with top surface kept at To but other surfaces being adiabatic. Design/methodology/approach Finite element method is used to solve the governing equations. Findings It is observed that the cavity exhibits unique heat transfer behavior as compared to regular cavity. The cases of boundary conditions are found to affect the heat transfer rate in the porous cavity. Originality/value This is original work representing the heat transfer in irregular porous cavity with various boundary conditions. This work is neither being published nor under review in any other journal.

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