Energy distributions and effective temperatures in the packing of elastic sheets

In recent years cool white dwarfs have been studied for various aspects ( see e.g.Winget et al.,1987 Winget and van Horn, 1987, Koester, 1987, Llebert, 1980) and much effort has been Invested in attempts to interpret the energy distributions of these stars ( Greenstein, 1984, Zeldler-K.T. et al, 1986, Llebert et al., 1987, and others). However, it seems that in spite of these efforts the spectra in particular of the very cool objects with effective temperatures below about 6000 K are not yet fully under-stood, since they are extremely diverse and each objects needs special consideration. In addition, the analyses are extremely difficult because the principal constiuents of the atmospheres ( H, He ) and elements, which may donate the majority of electrons, are essentially invisible. Since usually only one ionlsatlon stage of an element is present, this implies that the gas pressure Pg is high ( compared e.g. to the solar photosphere ), the accurate value of Pg, however, cannot be determined reliably.

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

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732447 ◽

2018 ◽

Vol 613 ◽

pp. A24 ◽

Cited By ~ 2

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.

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Analytical model of a magnetopause with countercurrents: multicomponent plasma with arbitrary particle energy distributions

10.5194/egusphere-egu21-11963 ◽

2021 ◽

Author(s):

Anton Nechaev ◽

Vitaly Kocharovsky ◽

Vladimir Kocharovsky

Keyword(s):

Energy Distribution ◽

Analytical Model ◽

Energy Content ◽

Magnetic Transition ◽

Collisionless Plasma ◽

Distribution Functions ◽

Magnetic Clouds ◽

Energy Distributions ◽

Current Sheets ◽

Effective Temperatures

We propose an analytical model for a distributed current sheet separating two regions of anisotropic collisionless plasma with different values of magnetization and different effective temperatures of the energy distributions of electrons and ions [1, 2]. Namely, we find a solution to the Vlasov&#8211;Maxwell equations in the form of a superposition of arbitrary isotropic distribution functions of particle energy, each multiplied by a Heaviside step function of one of the projections of the generalized momentum. This solution admits the shear of magnetic field lines and the presence of several ion components with different effective temperatures and localized countercurrents with arbitrary densities and spatial shifts.It is shown that a certain choice of the energy distribution of particles (Maxwellian, kappa, and others) determine only the quantitative, not qualitative, properties of the constructed models. Sheets containing several fractions of particles with countercurrents, shifted relative to each other in space and having different scales, allow multiple non-monotonic changes in the magnetic field value and direction. The total thickness of the current sheet is determined by the values of shifts between the currents of the plasma fractions with the highest energy content and by the typical gyroradii of their particles.We carried out particle-in-cell simulations of the analytically constructed magnetic transition layers in one-dimensional and two-dimensional geometries. The stability of the simplest models of the considered class is demonstrated, which is consistent with qualitative estimates of stability against Weibel-type perturbations.The proposed models make it possible to interpret modern data of satellite observations of multicomponent current sheets in the regions of the magnetopause and the bow shock, solar wind magnetic clouds and high coronal magnetic structures, and to analyze their fine structure taking into account the observed suprathermal, nonequilibrium particle fractions.The investigation of stability of current sheets was supported by the Russian Science Foundation under grant No. 20-12-00268.1. Kocharovsky V. V., Kocharovsky Vl. V., Martyanov V. Yu., Nechaev A. A. An analytical model for the current structure of the magnetosheath boundary in a collisionless plasma // Astron. Lett. 2019. V. 45, No. 8. P. 551&#8211;564. doi:10.1134/S1063773719080048 .2. Kocharovsky V. V., Kocharovsky Vl. V., Nechaev A. A. Analytical model of a magnetopause in a multicomponent collisionless plasma with a kappa energy distribution of particles // Doklady Physics. 2021. V. 496. In press.

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Applications of Narrow-Band Photometry in the Study of Peculiar Red Giants

Symposium - International Astronomical Union ◽

10.1017/s0074180900002333 ◽

2000 ◽

Vol 177 ◽

pp. 127-140

Author(s):

Robert F. Wing

Keyword(s):

Near Infrared ◽

Narrow Band ◽

Red Giants ◽

Late Type ◽

Energy Distributions ◽

Synthetic Spectra ◽

Continuum Energy ◽

Qualitative Classification ◽

Effective Temperatures ◽

Classification Recognition

Narrow-band photometry, carried out with filters or spectrum scanners, is useful for measuring molecular bandstrengths and continuum energy distributions in late-type stars. This review emphasizes observations by the writer on three different multicolor photometric systems in the near infrared (0.75 − 4.0 μm); a summary of available data is given. While applications to date have been primarily qualitative (classification, recognition of peculiarities, relative temperatures), future applications are expected to be quantitative (determinations of effective temperatures, luminosities, and abundances) and based upon comparison with synthetic spectra.

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Calculated Energy Distributions for SN II

International Astronomical Union Colloquium ◽

10.1017/s0252921100094197 ◽

1988 ◽

Vol 108 ◽

pp. 412-414

Author(s):

P.H. Hauschildt ◽

W. Spies ◽

R. Wehrse ◽

G. Shaviv

Keyword(s):

Ir Spectra ◽

Spherical Geometry ◽

Energy Distributions ◽

Density Profiles ◽

Continuous Processes ◽

Uv And Ir Spectra ◽

Effective Temperatures ◽

Potential Methods ◽

Good Agreement ◽

Large Grid

AbstractWe have calculated a large grid of hydrogen-rich supernova photospheres, in which radii, effective temperatures, density profiles, and expansion velocities have been varied. Spherical geometry, radiative equilibrium and LTE level populations are assumed. In the quasi-exact radiative transfer, the dilution of the radiation field, and scattering as well as absorption (by all relevant continuous processes and up to 150 000 lines in some models) are accurately considered. Good agreement can be obtained with the UV and IR spectra of supernovae 1979C, 1980K, and 1987A as observed during the coasting phase. Potential methods of parameter determinations for SN II are briefly discussed.

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Energy Distributions and Fundamental Parameters of 6 A Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100017644 ◽

1993 ◽

Vol 137 ◽

pp. 156-158

Author(s):

R. Monier

Keyword(s):

Effective Temperature ◽

Surface Gravity ◽

Infrared Photometry ◽

Flux Method ◽

Energy Distributions ◽

Fundamental Parameters ◽

Effective Temperatures ◽

Best Fit ◽

Angular Diameters

AbstractThe energy distributions (EDs) of 6 peculiar (3 Aps and 3 λ Bootis) stars are presented from 1200Ȧ up to about 12000Ȧ. For those stars having infrared photometry, the integrated flux from 1200& to 22000Å has been calculated and the Infrared Flux Method (IRFM, Blackwell and Shallis, 1977) applied to derive effective temperatures and angular diameters. For all stars, the effective temperature Teff, the surface gravity logg and metallicity [M/H] were also derived by matching the EDs to a grid of model atmospheres. A chisquare techniques is used to sort out the best fit to the observed EDs.

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Wolf-Rayet nebulae - Enrichment in He and N and effective temperatures of Wolf-Rayet stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900157006 ◽

1987 ◽

Vol 122 ◽

pp. 457-458

Author(s):

Michael R. Rosa

Keyword(s):

Mass Loss ◽

Chemical Evolution ◽

Observational Constraints ◽

Energy Distributions ◽

Chemical Surface ◽

Lyman Continuum ◽

Ionization Structure ◽

Continuum Region ◽

Effective Temperatures ◽

Central Stars

Nebulae surrounding isolated Pop I WR stars provide observational constraints on as yet poorly determined chemical surface abundances and FUV energy distributions of their central stars. An integral of the mass loss history and the chemical evolution is stored in those parts of the nebulae that have suffered only very little mixing with the ISM (cf. Kwitter 1984). Effective temperatures in the Lyman continuum region are reflected in the ionization structure of oxygen and sulfur (cf. Mathis 1982). For intrinsic problems involved refer to the papers cited above.

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Mathematical Assessment of Physical and Chemical Processes from the Middle B to the Early F Type Main Sequence Stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317005531 ◽

2017 ◽

Vol 12 (S330) ◽

pp. 362-363

Author(s):

Kutluay Yüce ◽

Saul J. Adelman

Keyword(s):

Main Sequence ◽

Stellar Atmospheres ◽

Stellar Winds ◽

Main Sequence Stars ◽

Energy Distributions ◽

Elemental Abundances ◽

Effective Temperatures ◽

Evolutionary Paths ◽

Physical And Chemical ◽

Hr Diagram

AbstractThe middle B to the early F Main Sequence stars have some of the most quiet stellar atmospheres. In this part of the HR diagram we find stars with atmospheres in radiative equilibrium. They lack the convective circulations of the middle F and cooler stars and the massive stellar winds of hotter stars. When stars of different mass evolve off the Main Sequence in this part of the HR Diagram their evolutionary paths do not cross initially. Thus stars with the same effective temperature and surface gravity have the same luminosity and mass. By comparing their elemental abundances, we might be able to identify physical processes which cause any differences in their abundances. Here we begin with stars whose effective temperatures and surface gravities are similar, and which have been analyzed by us using spectra obtained from the Dominion Astrophysical Observatory (DAO). Improvements in our knowledge of the energy distributions of stars (for example via GAIA measurements) should lead to improved estimates of stellar effective temperatures and surface gravities.

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Effective temperatures of magnetic chemically peculiar stars from full spectral energy distributions

Monthly Notices of the Royal Astronomical Society ◽

10.1111/j.1365-2966.2008.12856.x ◽

2008 ◽

Vol 385 (1) ◽

pp. 481-492 ◽

Cited By ~ 10

Author(s):

Ł. Lipski ◽

K. Stȩpień

Keyword(s):

Spectral Energy ◽

Spectral Energy Distributions ◽

Energy Distributions ◽

Chemically Peculiar ◽

Peculiar Stars ◽

Effective Temperatures ◽

Chemically Peculiar Stars

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Stellar Absolute Fluxes and Energy Distributions from 0.32 to 4.0 μM

Symposium - International Astronomical Union ◽

10.1017/s0074180900078876 ◽

1985 ◽

Vol 111 ◽

pp. 225-252 ◽

Cited By ~ 1

Author(s):

D. S. Hayes

Keyword(s):

Energy Distribution ◽

Recent Progress ◽

Special Problem ◽

Secondary Standard ◽

The Sun ◽

Energy Distributions ◽

Absolute Flux ◽

Effective Temperatures ◽

The Absolute ◽

Special Case

The absolute fluxes and energy distributions of stars are the foundation of the calibration of fundamental effective temperatures and bolometric corrections. In this paper I will review recent progress in the calibration of absolute fluxes and energy distributions in the visual and IR parts of the spectrum. In the visual, the calibration of the absolute flux and energy distribution of Vega has settled down well, and the remaining difficulties include the lack of a worldwide common list of brighter secondary standard stars, the lack of enough satisfactory fainter secondary standard stars and the possibility of variability in Vega. In the IR, the process of arriving at a dependable and accurate calibration, and of linking it to commonly used photometric systems, is in its infancy. A final, and rather special problem, is the question of the calibration of the Sun. The Sun is a special case both because it is so well studied astrophysically and because its extreme brightness makes it very difficult to calibrate photometrically. Some progress has recently been made on the calibration of the absolute flux and energy distribution of the Sun, and I will discuss this work.

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