共查询到20条相似文献，搜索用时 545 毫秒
1.
Terry W. Edwards 《Astrophysics and Space Science》1970,6(3):436-449
A rather general first order linearized perturbation theory is derived with which one can calculate a quasi-static equilibrium stellar interior model if given an initial approximation thereto. The process developed is applicable to both static and evolutionary models, wherein slightly different physical assumptions (e.g. gas characteristics) or physical conditions (e.g. matter composition) are imposed. The correction to the given model is obtained through bi-directional quadrature with fitting at an intermediate position; however, no trial integrations are necessary. 相似文献
2.
Using the Andersen (1991) data on the mass, absolute visual magnitude, the effective surface temperature and the bolometric corrections, new calibrations for the mass vs. absolute visual magnitude and for the bolometric correction vs. effective surface temperature have been derived. Comparison between the latest evolutionary models with the empirical data has been made to test the evolutionary models for the purpose of stellar population studies. 相似文献
3.
A. J. Hillel 《Astrophysics and Space Science》1973,25(2):413-432
It is argued that a Salpeter initial luminosity function is consistent with the observed integral properties of giant elliptical galaxies if the gaseous material lost by evolving stars can be retained in the system for times of the order of 108 yr. One model which emerges is of a highly condensed system consisting mainly of metal-poor population II stars with an admixture (1.5%–15%) of super-metalrich stars born from the gaseous debris, which at the present time constitutes 0.05%–0.5% of the total mass. HighM/L ratios result from obscuration of the starlight, and the missing radiation reappears in the form of a strong I-R flux at wavelengths of the order of 100 . The difference in colour betweengE anddE galaxies is explained in terms of interstellar reddening, and strong interstellar metallic absorption lines are also expected. The model leads to a negligible evolutionary correction to the cosmological deceleration parameterq
0. An alternative model, in which the stars arenot metal poor, has a more condensed, heavily obscured nucleus, surrounded by the unobscured central bulge of the Galaxy which provides most of the light. In this version a large evolutionary correction would be required. 相似文献
4.
Rosa M. González Delgado 《Astrophysics and Space Science》2009,324(2-4):231-239
Stellar population models are a very useful tool to derive the stellar cluster age and luminosity mass from its integrated light. Evolutionary synthesis models depend on the stellar evolutionary tracks and the stellar libraries used to predict the spectral energy distribution of the stellar populations. In this review, I briefly comment on the new models that have incorporated the new evolutionary tracks with rotation and new computations for the evolutionary tracks of the TP-AGB. A more extended summary is also given of the current status of the most recent high-resolution stellar libraries at optical wavelengths and their implementation in evolutionary synthesis models. A comparison of the results obtained fitting the optical spectra of LMC and SMC stellar clusters with different high spectral resolution evolutionary synthesis models is also presented. 相似文献
5.
An evolutionary model for the M31 inner disk population is described, which at age 12 billion years agrees closely with the narrow-band colors and line indices recently measured by Spinradet al. (1971), and with the broad-band colors from 0.36 to 3.4 . Assuming that gE galaxies have the same stellar population as the M31 inner disk, this model is used to derive evolutionary effects in cosmology. Interpretation of the magnitude-redshift relation is substantially affected, since the evolutionary correction to V magnitudes at redshift 0.2 may be 0.09 mag. if H0=100 km s–1 Mpc–1, or 0.25 mag. ifH
0=50. Changes in some line strengths may be observable at redshift 0.46, showing the younger stellar population at earlier times. Our results differ from estimates by other authors, also based on the assumption that the gE and disk populations are identical, that the photometry of Spinradet al. (1971) precludes a significant rate of evolution. One reason for the difference is that our model has an unexpectedly shallow luminosity function just below the main sequence turnoff; another reason is that authors in the past have used the change in absolute V magnitude as the evolutionary correction, whereas the appropriate quantity is the change in absolute magnitude at theemitted wavelengths, and evolution is more rapid at these shorter wavelengths. 相似文献
6.
D. Froebrich S. Schmeja M. D. Smith R. S. Klessen 《Monthly notices of the Royal Astronomical Society》2006,368(1):435-446
The rates at which mass accumulates into protostellar cores can now be predicted in numerical simulations. Our purpose here is to develop methods to compare the statistical properties of the predicted protostars with the observable parameters. This requires (1) an evolutionary scheme to convert numerically derived mass accretion rates into evolutionary tracks and (2) a technique to compare the tracks to the observed statistics of protostars. Here, we use a 3D Kolmogorov–Smirnov test to quantitatively compare model evolutionary tracks and observations of Class 0 protostars.
We find that the wide range of accretion functions and time-scales associated with gravoturbulent simulations naturally overcome difficulties associated with schemes that use a fixed accretion pattern. This implies that the location of a protostar on an evolutionary track does not precisely determine the present age or final accrued mass. Rather, we find that predictions of the final mass for protostars from observed Tbol – L bol values are uncertain by a factor of 2 and that the bolometric temperature is not always a reliable measure of the evolutionary stage. Furthermore, we constrain several parameters of the evolutionary scheme and estimate a lifetime of Class 0 sources of 2–6 × 104 yr , which is related to the local free-fall time and thus to the local density at the onset of the collapse. Models with Mach numbers smaller than six are found to best explain the observational data. Generally, only a probability of 70 per cent was found that our models explain the current observations. This is caused by not well-understood selection effects in the observational sample and the simplified assumptions in the models. 相似文献
We find that the wide range of accretion functions and time-scales associated with gravoturbulent simulations naturally overcome difficulties associated with schemes that use a fixed accretion pattern. This implies that the location of a protostar on an evolutionary track does not precisely determine the present age or final accrued mass. Rather, we find that predictions of the final mass for protostars from observed T
7.
8.
R. M. González Delgado M. Cerviño L. P. Martins C. Leitherer P. H. Hauschildt 《Monthly notices of the Royal Astronomical Society》2005,357(3):945-960
We present the single stellar population (SSP) synthesis results of our new synthetic stellar atmosphere models library with a spectral sampling of 0.3 Å, covering the wavelength range from 3000 to 7000 Å for a wide range of metallicities (twice solar, solar, half solar and 1/10 solar). The stellar library is composed of 1650 spectra computed with the latest improvements in stellar atmospheres. In particular, it incorporates non-local thermodynamic equilibrium (LTE) line-blanketed models for hot ( T eff ≥ 27 500 K) , and LTE line-blanketed models (Phoenix) for cool (3000 ≤ T eff ≤ 4500 K) stars. Because of the high spectral resolution of this library, evolutionary synthesis models can be used to predict the strength of numerous weak absorption lines and the evolution of the profiles of the strongest lines over a wide range of ages. The SSP results have been calculated for ages from 1 Myr to 17 Gyr using the stellar evolutionary tracks provided by the Geneva and Padova groups. For young stellar populations, our results have a very detailed coverage of high-temperature stars with similar results for the Padova and Geneva isochrones. For intermediate and old stellar populations, our results, once degraded to a lower resolution, are similar to the ones obtained by other groups (limitations imposed by the stellar evolutionary physics notwidthstanding). The limitations and advantages of our models for the analysis of integrated populations are described. The full set of the stellar library and the evolutionary models are available for retrieval at the websites http://www.iaa.csic.es/~rosa and http://www.iaa.csic.es/~mcs/sed@ , or on request from the first two authors. 相似文献
9.
基于伪距测量的钟差计算模型 总被引：1，自引：0，他引：1
基于伪距和钟差定义,讨论了无线电时间比对的基本原理。在此基础上,详细推导了地心非旋转坐标系中一般意义下基于伪码测距模式的钟差计算模型,并通过坐标变换,给出了地固系中的实用计算模型。对地回系计算模型的进一步分析表明：卫星在地固系运动速度引起的改正项与sagnac效应项是完全不同的两项改正;对于GEO卫星,sagnac效应项最大约为200ns,其地固系运动速度引起的改正约为1ns;而对于MEO卫星,sagnac效应项最大为120ns,其地固系运动速度引起的改正约为1200ns。 相似文献
10.
利用3天22个测站的Lageos-1激光测距资料,解算出卫星的一条轨道,再利用此轨道和地面测站检验原有的大气折射模型.得到定轨常用的Marini(1973)模型以及Yan (1999)模型、UNSW932模型、Cfa2.2(1985)模型等的改正特点. 相似文献
11.
The models of non-rotating and rotating 2.31M
\ stars of Population I composition have been calculated, starting at the threshold of stability. A 2.31M
\ star was chosen to compare the results with the observational parameters of the primary component of the well-known detached binary YZ Cassiopeiae. The effects of rotation on the internal structure during the evolution of the star were studied by constructing sequences of axisymmetric rotating models under the assumption that angular momentum was conserved according to a predetermined angular velocity distribution depending on the structure of the star.The first section of this paper deals with effects of rotation on the evolutionary behaviours of the 2.31M
\ star through the pre-Main-Sequence evolution as well as the zero-age Main Sequence.In the second section of this paper, the evolutionary studies have been extended up to near-hydrogen exhaustion phase in order to obtain a theoretical model corresponding to the given mass and radius of the primary component of YZ Cassiopeiae. The theoretical models were found to be in a good agreement with observational parameters. The computed rotating models of the primary of YZ Cassiopeiae indicates that its evolutionary age is 6.01×108 years; and the central hydrogen content 0.183 — which means that about 75% of its original value was depleted. 相似文献
12.
Ralf Kotulla Uta Fritze Peter Weilbacher Peter Anders 《Monthly notices of the Royal Astronomical Society》2009,396(1):462-484
galev (GALaxy EVolution) evolutionary synthesis models describe the evolution of stellar populations in general, of star clusters as well as of galaxies, both in terms of resolved stellar populations and of integrated light properties over cosmological time-scales of ≥13 Gyr from the onset of star formation shortly after the big bang until today.
For galaxies, galev includes a simultaneous treatment of the chemical evolution of the gas and the spectral evolution of the stellar content, allowing for what we call a chemically consistent treatment: we use input physics (stellar evolutionary tracks, stellar yields and model atmospheres) for a large range of metallicities and consistently account for the increasing initial abundances of successive stellar generations.
Here we present the latest version of the galev evolutionary synthesis models that are now interactively available at http://www.galev.org . We review the currently used input physics, and also give details on how this physics is implemented in practice. We explain how to use the interactive web interface to generate models for user-defined parameters and also give a range of applications that can be studied using galev , ranging from star clusters, undisturbed galaxies of various types E–Sd to starburst and dwarf galaxies, both in the local and the high-redshift Universe. 相似文献
For galaxies, galev includes a simultaneous treatment of the chemical evolution of the gas and the spectral evolution of the stellar content, allowing for what we call a chemically consistent treatment: we use input physics (stellar evolutionary tracks, stellar yields and model atmospheres) for a large range of metallicities and consistently account for the increasing initial abundances of successive stellar generations.
Here we present the latest version of the galev evolutionary synthesis models that are now interactively available at http://www.galev.org . We review the currently used input physics, and also give details on how this physics is implemented in practice. We explain how to use the interactive web interface to generate models for user-defined parameters and also give a range of applications that can be studied using galev , ranging from star clusters, undisturbed galaxies of various types E–Sd to starburst and dwarf galaxies, both in the local and the high-redshift Universe. 相似文献
13.
C.S. Möller U. Fritze–V. Alvensleben K.J. Fricke D. Calzetti 《Astrophysics and Space Science》2001,276(2-4):799-806
As a tool for interpreting nearby and high-redshift galaxy data from the optical to K-band we present our chemically consistent spectrophotometric evolutionary synthesis models. These models take into account
the increasing initial metallicity of successive stellar generations using recently published metallicity-dependent stellar
evolutionary tracks, stellar yields and model atmosphere spectra. The influence of the metallicity is analysed. Dust absorption
is included on the basis of gas content and abundance as it varies with time and galaxy type. We compare our models with IUE
template spectra and are able to predict UV fluxes for different spectral types. Combining our models with a cosmological
model we obtain evolutionary and k corrections for various galaxy types and show the differences from models using only solar metallicity input physics as a
function of redshift, wavelength band and galaxy type.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
R. D. Rohrmann † 《Monthly notices of the Royal Astronomical Society》2001,323(3):699-712
We present a detailed calculation of model atmospheres for DA white dwarfs. Our atmosphere code solves the atmosphere structure in local thermodynamic equilibrium with a standard partial linearization technique, which takes into account the energy transfer by radiation and convection. This code incorporates recent improved and extended data base of collision-induced absorption by molecular hydrogen. We analyse the thermodynamic structure and emergent flux of atmospheres in the range 2500 T eff 60 000 K and 6.5log g 9.0. Bolometric correction and colour indices are provided for a subsample of the model grid. Comparison of the colours is made with published observational material and results of other recent model calculations.
Motivated by the increasing interest in helium-core white dwarfs, we analyse the photometric characteristics of these stars during their cooling, using evolutionary models recently available. Effective temperatures, surface gravities, masses and ages have been determined for some helium-core white dwarf candidates, and their possible binary nature is briefly discussed. 相似文献
Motivated by the increasing interest in helium-core white dwarfs, we analyse the photometric characteristics of these stars during their cooling, using evolutionary models recently available. Effective temperatures, surface gravities, masses and ages have been determined for some helium-core white dwarf candidates, and their possible binary nature is briefly discussed. 相似文献
15.
Nobuo Arimoto 《Astrophysics and Space Science》1981,74(2):319-331
Recent evolutionary computations of stars in the globular clusters show that the star ascending up the red giant branch decreases its luminisity temporarily when the outward advancing hydrogen-burning shell passes over the discontinuity in the chemical compositions, which is the trace of maximum inward penetration of the convective envelope in the previous subgiant stage. To understand the physical circumstance of this luminosity drop, the semi-analytical approach using the classical red giant model was applied. The difference of the present analysis from those with usual models of the red giant is that the gradient and the discontinuity in the hydrogen profile, which were usually neglected in the classical red giant model, in the region into which the hydrogen-burning shell advances were taken into account explicitly. It was found that the luminosity would always drop at the critical stage, the stage when the hydrogen-burning shell just passes over the discontinuity. It was also pointed out that the luminosity drop depends on the time step chosen for constructing the stellar evolutionary models and computations with crude time step would fail to catch up this phenomenon. 相似文献
16.
《Planetary and Space Science》1999,47(10-11):1175-1182
We present evolutionary sequences for Jupiter and Saturn, based on new non-gray model atmospheres, which take into account the evolution of the solar luminosity and partitioning of dense components to deeper layers. The results are used to set limits on the extent to which possible interior phase separation of hydrogen and helium may have progressed in the two planets. When combined with static models constrained by the gravity field, our evolutionary calculations constrain the helium mass fraction in Jupiter to be between 0.20 and 0.27, relative to total hydrogen and helium. This is consistent with the Galileo determination. The helium mass fraction in Saturn’s atmosphere lies between 0.11 and 0.21, higher than the Voyager determination. Based on the discrepancy between the Galileo and Voyager results for Jupiter, and our models, we predict that revised observational results for Saturn will yield a higher atmospheric helium mass fraction relative to the Voyager value. 相似文献
17.
Using the annual GPS observational tropospheric zenith delay data and meteorological data obtained at 36 globally distributed IGS stations in 2003, we have estimated the accuracy and range of application of two often-used models of tropospheric delay correction (the Hopfield and Saastamoinen models), and of a more recent model (the EGNOS model). We point out some defects in the Hopfield model and show that the EGNOS model can be used as the correction model of the tropospheric zenith delay for the GNSS real-time positioning and navigation. 相似文献
18.
Conventional evolutionary models for Mars adopt a dry mantle solidus. Taking into account the condensation conditions in the preplanetary nebula in the accretion zone of Mars, it can be concluded that large amounts of water or hydrated silicates have condensed in those regions. Therefore, water influences significantly the melting behaviour and the viscosity of the silicatic material. A model for the calculation of the thermal history of a planet is constructed. On this basis, and use of water — saturated solidus — it is possible to derive that the core is not liquid, as given in models employing a dry mantle solidus, but solid to a large extent, which prevents the operation of a large-scale dynamo and explains in that way the lack of a magnetic field. With these assumptions one can construct a possible evolutionary scheme that covers early crust differentiation, a hot thermal past and the missing magnetic field at present. 相似文献
19.
20.
《天文和天体物理学研究(英文版)》2018,(11)
The regional BeiDou Satellite System, or BDS2, broadcasts a differential correction as Equivalent Satellite Clock Correction to correct both orbit and satellite clock errors. For the global BDS, or BDS3, satellite orbit and clock corrections conforming with RTCA standards will be broadcast to authorized users. The hybrid constellation and regional monitoring network pose challenges for the high precision separation of orbit and satellite clock corrections. Three correction models of kinematic,dynamic and Two-way Satellite Time Frequency Transfer(TWSTFT)-based dynamic were studied to estimate the satellite orbit and clock corrections. The correction accuracy of the three models is compared and analyzed based on the BDS observation data. Results show that the accuracies(root mean square, RMS) of dual-frequency real-time positioning for the three models are about 1.76 m, 1.78 m and 2.08 m respectively, which are comparable with the performance of WAAS and EGNOS. With dynamic corrections, the precision of Precise Point Positioning(PPP) experiments may reach about 23 cm after convergence. 相似文献