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1.
The longitudinal magnetic field measured using the Fe I λ 525 and Fe I λ 524.7 nm lines and global magnetic field of the sun
differ depending on the observatory. To study the cause of these discrepancies, we calculate the H
‖(525)/H
‖(524.7) ratios for various combinations of magnetic elements and compare them with the corresponding observed values. We use
the standard quiet model of the solar photosphere suggesting that there are magnetic fields of different polarities in the
range between zero and several kilogauss. The magnetic element distribution is found as a function of magnetic field strength
and the parameters of this distribution are determined for which the calculated H
‖(525)/H
‖(524.7) ratio agrees with the observed one. The sigma-components are found to be shifted differently for various points of
the Fe I λ 525 nm profile calculated for the inhomogeneous magnetic field. The farther the point is from the line center,
the larger the sigma-components shift. Such a peculiarity of the profiles may be responsible for the discrepancies in the
measured values of the global magnetic field obtained at different observatories. The increase in modulus of the global magnetic
field during the maxima of solar activity can be due to a larger fraction of magnetic elements with kilogauss magnetic fields. 相似文献
2.
Based on our spectroscopic observations of the variable planetary nebula IC 4997 in 2003–2009, we have obtained the relative
fluxes in optical emission lines. The interstellar extinction c = 0.35 has been found from the Balmer decrement by taking into account the effect of self-absorption in hydrogen lines in
dense nebular regions. The variations in the Balmer decrement point to variability of the self-absorption and circumstellar
extinction. We have investigated the variations in the relative intensities of some spectral lines and their ratios with time.
The drop in the ratios F(λ4363)/F(Hγ) and F(λ363)/F(λ4959) that began back in 1990–1995 has continued, suggesting a decrease in the electron density and temperature in the central
nebular region. The ratio F(λ6731)/F(λ6717) has remained constant. It gives an estimate for the electron density in the outer regions of IC 4997, N
e
∼ 104 cm−3. 相似文献
3.
Daniel Thomas Ralf Bender Ulrich Hopp Claudia Maraston Laura Greggio 《Astrophysics and Space Science》2003,284(2):599-602
We present kinematics and stellar population properties of 17 dwarf early-type galaxies in the luminosity range -14 ≥ M
B ≥ -19. Our sample fills the gap between the intensively studied giant elliptical and Local Group dwarf spheroidal galaxies.
The dwarf ellipticals of the present sample have constant velocity dispersion profiles within their effective radii and do
not show significant rotation, hence are clearly anisotropic. The dwarf lenticulars, instead, rotate faster and are, at least
partially, supported by rotation. From optical Lick absorption indices, we derive metallicities and element abundances. Combining
our sample with literature data of the Local Group dwarf spheroidals and giant ellipticals, we find a surprisingly tight linear
correlation between metallicity and luminosity over a wide range: -8 ≥ M
B ≥ -22. The α/Fe ratios of our dwarf ellipticals are significantly lower than the ones of giant elliptical galaxies, which
is in agreement with spectroscopy of individual stars in Local Group dwarf spheroidals. Our results suggest the existence
of a clear kinematic and stellar population dichotomy between dwarf and giant elliptical galaxies. This result is important
for theories of galaxy formation, because it implies that present-day dwarf ellipticals are not the fossiled building blocks
of giant ellipticals.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
Near Infrared spectroscopic observations (1.2–2.4µm) of two condensations (HH 1A & HH 1G) of Herbig-Haro object 1 are used to explore the nature of its molecular shocks and extinction. The H2 emission lines display a more complex behaviour than that accounted for C or J type shock models. The extinction, determined from the ratio of [Fe II] 1.257 & 1.644µm, is higher than what is expected from optical [S II] measurements, and it may indicate real discrepancies between the optical and IR regions of the ISM extinction curve. 相似文献
5.
Compressible homogeneous spheres with constant adiabatic index γ were studied for their dynamical stability by Chandrasekhar
and he found that for each value of u (≡ mass to size ratio), there is a value of γ = γc, such that for γ < γc, the configuration is dynamically unstable. On examining the properties of the Chandrasekhar's spheres (homogeneous spheres
with constant γ) it is found that these spheres are non-isentropic, and the speed of sound within these spheres is finite.
The authors find that (i) for the causality condition to be fulfilled throughout the configuration, the value of γ ≤ [2/(surface
redshift)], (ii) for a given value of u, the binding coefficient, αr = (Mr -M)/M, vanishes for some value of γ = γb and for all the values of γ < γb the configurations are unbound, and (iii) for u≤ (1/3), one can find configurations which are bound, dynamically stable, and the speed of sound is less than that of light
throughout the configuration, whereas, for u >(1/3), the physically viable models of homogeneous density distribution are not possible. If the configuration is considered
to be isentropic, then both γ and the speed of sound become infinite throughout the configuration.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
Rosaria Tantalo 《Astrophysics and Space Science》2001,276(2-4):1189-1199
In this paper we present a recent attempt to infer the age, metallicity and abundance ratios for a selected sample of elliptical
galaxies, adopting the line-strength indices Hβ, Mg2 and 〈Fe 〉, which respond in different ways to different parameters such as age (Hβ), metallicity and abundance ratios (〈Fe〉 and Mg2).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
We discuss the equilibrium solutions of four different types of collinear four-body problems having two pairs of equal masses.
Two of these four-body models are symmetric about the center-of-mass while the other two are non-symmetric. We define two
mass ratios as μ
1 = m
1/M
T and μ
2 = m
2/M
T, where m
1 and m
2 are the two unequal masses and M
T is the total mass of the system. We discuss the existence of continuous family of equilibrium solutions for all the four
types of four-body problems. 相似文献
8.
Observations of the central intensity of the Ca ii K and 849.8 nm lines are used to derive the ratios of the oscillation power in the frequency ranges of the “five-minute”
(W
5) and “three-minute” (W
3) oscillations. It is shown that at high significance level ratios, (W
5/W
3) >1 at coronal hole bases, and W
5/W
3 ≈1 in quiet chromospheric areas far from holes. 相似文献
9.
This review presents a selection of recent highlights of observations of R Coronae Borealis variables. Emphasis is placed
on an abundance analysis of a complete sample (18 stars) of the warm galactic RCBs. It is shown that 14 of the 18 have very
similar compositions: the iron mass fraction ranges about a factor of 3 around the solar value (assuming C/He = 3%) but abundance
ratios X/Fe for elements from Na to Ba show little variation. By contrast, the other 4 stars are deficient in iron but not
in Na, Si, S and some other elements. With for example, [Si/Fe] ≃ 2, the quartet is indeed ‘peculiar’. One of the quartet,
V854 Cen shows depletions of elements (other than CNO) similar to the depletions seen in interstellar medium corresponding
to average logn(H
tot) = − 1.5. Scenarios for creating RCB from normal single and double stars are summarised.
Invited review talk presented at the Asia-Pacific regional IAU meeting held at Pune from 16–20 August 1993. 相似文献
10.
We calculated 240 model atmospheres of carbon giants with high carbon abundance (2800 K ≤ T
eff ≤ 3400 K, 0.06 ≤ log(C/O) ≤ 2.7). This set of models was used for modelling of the energy distribution in the spectrum of
an evolved carbon star DY Per demonstrating photometric features of the R CrB type stars. Most of the models are metal-poor
(−3.5 ≤ [Fe/H] < 0) and a portion of them was calculated with the hydrogen deficiency (1/9 ≤ H/He < 9/1). The calculations
of the models were carried out taking into account specific for carbon stars sources of opacity in the frame of the classic
approaches. The opacity sampling method was used to calculate the opacity due to the atomic and molecular line absorption. 相似文献
11.
H. Kuntschner 《Astrophysics and Space Science》2001,276(2-4):885-891
We have measured central line strengths for a complete sample of early-type galaxies in the Fornax Cluster comprising 11 elliptical
and 11 lenticular galaxies, more luminous than M
B=–17. We find that the centres of Fornax ellipticals follow the locus of galaxies of fixed age in Worthey's models and have
metallicities varying roughly from half to 2.5 times solar. The centres of (relatively low luminosity) lenticular galaxies,
however, exhibit a substantial spread to younger luminosity-weighted ages indicating amore extended star formation history.
Our conclusions are based on two age/metallicity diagnostic diagrams in the Lick/IDS system comprising established indices
such as [MgFe]and Hβ as well as new and more sensitive indices, such as Fe3and H
. The inferred difference in the age distribution between lenticular and elliptical galaxies is a robust conclusion as the
models generate consistent relative ages using different age and metallicity indicators even though the absolute ages remain
uncertain. The absolute age uncertainty is caused mainly by the effects of non-solar abundance ratios, which are not accounted
for in the stellar population models. We find that Es are generally overabundant in magnesium and the most luminous galaxies
show stronger overabundances. The luminosity-weighted stellar populations of young S0s are consistent with solar abundance
ratios or a weak Mg under abundance. Two of the faintest lenticular galaxies in our sample have blue continua and extremely
strong Balmer-line absorptions suggesting starbursts <2 Gyr ago.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
By means of population synthesis models with variable α/Fe ratios we derive average ages, metallicities, and [α/Fe] element
enhancements for a sample of 126 field and cluster early-type galaxies. We find a clear positive relation between [α/Fe] and
velocity dispersion. Zero-point, slope, and scatter of this correlation are the same for cluster and field galaxies. In particular,
the [α/Fe] ratios and mean ages of cluster ellipticals are positively correlated. This strongly reinforces the view that the
[α/Fe] element enhancement in ellipticals is produced by star formation timescales rather than by variations of the initial
mass function. These results indicate that the more massive the galaxy, the shorter is its star formation timescale, and the
higher is the redshift of the bulk of star formation. This finding is not compatible with the predictions from models of hierarchical
galaxy formation. The lenticular and field galaxies of the investigated sample do not follow the correlation between age and
[α/Fe], but contain a non-negligible fraction of galaxies with young average ages and high [α/Fe] ratios.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
13.
C. Muthumariappan 《Journal of Astrophysics and Astronomy》2010,31(1):17-29
Interstellar extinction curves obtained from the ‘extinction without standard’ method were used to constrain the dust characteristics
in the mean ISM (R
V
= 3.1), along the lines of sight through a high latitude diffuse molecular cloud towards HD 210121 (R
V
= 2.1) and in a dense interstellar environment towards the cluster NGC 1977 (R
V
= 6.42). We have used three-component dust models comprising silicate, graphite and very small carbonaceous grains (polycyclic
aromatic hydrocarbons) following the grain size distributions introduced by Li & Draine in 2001. It is shown that oxygen,
carbon and silicon abundances derived from our models are closer with the available elemental abundances for the dust grains
in the ISM if F & G type stars atmospheric abundances are taken for the ISM than the solar. The importance of very small grains
in modelling the variation of interstellar extinction curves has been investigated. Grain size distributions and elemental
abundances locked up in dust are studied and compared at different interstellar environments using these three extinction
curves. We present the albedo and the scattering asymmetry parameter evaluated from optical to extreme-UV wavelengths for
the proposed dust models. 相似文献
14.
We consider a self consistent system of Bianchi Type-I cosmology and Binary Mixture of perfect fluid and dark energy. The
perfect fluid is taken to be obeying equations of state p
PF
=γρ
PF
with γ∈[0,1]. The dark energy is considered to be obeying a quintessence-like equation of state where the dark energy obeys equation
of state p
DE
=ωρ
DE
where ω∈[−1,0]. Exact solutions to the corresponding Einstein field equations are obtained. Some special cases are discussed and
studied. Further more power law models and exponential models are investigated. 相似文献
15.
In this paper, besides general definition of hardness ratio of gamma-ray bursts (GRBs), HR
32, we also presented new definitions of hardness ratios, HR
hl and HR
ll, then presented the results of correlation studies, examining the association between the hardness ratios and the spectral
fitting parameters (E
0 or E
peak, α, β) by using the GRB data observed by BATSE. The HR
hl is defined as the fluence of channel 4 divided by the sum of the fluences of channels 1 to 3,and the HR
ll is defined as the fluence of channel 3 divided by the sum of the fluences of channel 1 and 2. We found that E
0 and E
peak are correlated with hardness ratios, and β is only correlated with log (HR
hl). The α is not correlated with any hardness ratios in the total sample of GRBs, while it correlated with log (HR
ll) and log (HR
32) in the two subsets seperated at log (HR
ll) = 0.34 ×α +0.66, respectively. These results show that a harder spectra tends to be steeper and has a higher E
peak or E
0; HR
hl describes the spectral behaviors in high energy, while both of HR
ll and HR
32 reflect the spectral characteristics in low energy; the spectral behaviors in low energy are different for the two subsets.
We also presented a brief qualitative analysis discussion to the correlations and suggested that the correlations are caused
by both of intrinsic and cosmological effects, but intrinsic effects are dominant.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
E. A. Baranovsky V. G. Lozitsky V. P. Tarashchuk 《Kinematics and Physics of Celestial Bodies》2009,25(5):254-259
The spectra of two powerful flares with approximately the same intensities in the optical region but with different spectral
features and power in other regions are studied. One of them is the unique flare which occurred on October 28, 2003, importance
X17.2/4B, ranking third in magnitude among the recorded flares. Another occurred on September 1, 1990, 3B importance. The
flares vary in the Balmer decrement. The flare of October 28, 2003, has a ratio of I(Hβ)/I(Hα) = 1.47. This is the largest value for solar flares ever observed. The flares also differ in magnitude of the D Na I lines emission: the emission of the flare of October 28, 2003, is substantially larger than that of the other flare.
The chromosphere models of the flares are computed using the observed profiles of Balmer lines and D Na I lines. The satisfactory agreement of the calculated and observed profiles is obtained for the two-component models in
which a hot component occupies 6% of the area. The hot component of the chromosphere model is characterized with the dense
condensation available in the upper layers. For the flare of October 28, 2003, this condensation is located deeper and its
substance concentration is greater than that for another flare. The Hα line intensity for the model hot component alone is approximately 30 and the continuous spectrum intensity is approximately
3% of the undisturbed level. The photosphere model is computed using the observed profiles of photosphere lines for the flare
of October 28, 2003. It is found that very broad profiles of individual sigma-components of the Fe I λ 525.0 nm line may be
only explained by the presence of magnetic fields having different directions. A great difference is detected between values
of the magnetic field strength obtained in the splitting of sigma-components and those provided by simulation. 相似文献
17.
The radio recombination line intensities of heavy elements of helium, carbon and oxygen are calculated with accounting for
dielectronic recombination. Dielectronic recombination rates are determined accurate to the second order of a perturbation
theory and the rates are described as function of principal quantum number for helium-like atom or ion. Balance equations
are solved for the departure coefficients from LTE bn. The collision and spontaneous transition rates are accounted for the balance equations, in which non-equilibrium distribution
source is dielectronic recombination. Non-equilibrium amplification coefficients are found as functions of a medium temperature,
density and ion charge z = 1–3 for radio recombination lines.
Optical depths are calculated for the heavy element low-frequency lines with the numbers 300 > n > 1200. For the chosen electronic temperatures and densities Te = 0.8× 104–10× 104 K, Ne = 0.05–0.1 cm−3 the line optical depth is determined by the values τL∼ 0.1× 10−4–100× 10−4. Calculated for free-free transition rates, the optical depth is given by using the value τff∼ 10−2τL. 相似文献
18.
Elena DzifčÁKOVÁ 《Solar physics》2006,234(2):243-256
Changes in the excitation equilibrium of Feviii – Fe xv in the solar corona due to the electron non-thermal κ-distribution
are studied. The shape of the distribution affects the electron excitation rate and thus the relative intensities of the spectral
lines. Since the shape of the electron distribution function influences also the ionization equilibrium of Fe, both effects
change the final intensities of the lines. Possibilities for diagnostics of the shape of the electron distribution in the
solar corona are discussed. Synthetic spectrum of Fe for T = 1.58× 106 K and ne = 108 cm−3 is shown together with the synthetic spectra computed with DEM for the quiet Sun. 相似文献
19.
P. S. Negi 《Astrophysics and Space Science》2011,332(1):145-153
We construct for the first time, the sequences of stable neutron star (NS) models capable of explaining simultaneously, the
glitch healing parameters, Q, of both the pulsars, the Crab (Q≥0.7) and the Vela (Q≤0.2), on the basis of starquake mechanism of glitch generation, whereas the conventional NS models cannot give such consistent
explanation. Furthermore, our models also yield an upper bound on NS masses similar to those obtained in the literature for
a variety of modern equations of state (EOSs) compatible with causality and dynamical stability. If the lower limit of the
observational constraint of (i) Q≥0.7 for the Crab pulsar and (ii) the recent value of the moment of inertia for the Crab pulsar (evaluated on the basis of
time-dependent acceleration model of the Crab Nebula), I
Crab,45≥1.93 (where I
45=I/1045 g cm2), both are imposed together on our models, the models yield the value of matching density, E
b
=9.584×1014 g cm−3 at the core-envelope boundary. This value of matching density yields a model-independent upper bound on neutron star masses,
M
max≤2.22M
⊙, and the strong lower bounds on surface redshift z
R
≃0.6232 and mass M≃2.11M
⊙ for the Crab (Q≃0.7) and the strong upper bound on surface redshift z
R
≃0.2016, mass M≃0.982M
⊙ and the moment of inertia I
Vela,45≃0.587 for the Vela (Q≃0.2) pulsar. However, for the observational constraint of the ‘central’ weighted mean value Q≈0.72, and I
Crab,45>1.93, for the Crab pulsar, the minimum surface redshift and mass of the Crab pulsar are slightly increased to the values
z
R
≃0.655 and M≃2.149M
⊙ respectively, whereas corresponding to the ‘central’ weighted mean value Q≈0.12 for the Vela pulsar, the maximum surface redshift, mass and the moment of inertia for the Vela pulsar are slightly decreased
to the values z
R
≃0.1645, M≃0.828M
⊙ and I
Vela,45≃0.459 respectively. These results set an upper and lower bound on the energy of a gravitationally redshifted electron-positron
annihilation line in the range of about 0.309–0.315 MeV from the Crab and in the range of about 0.425–0.439 MeV from the Vela
pulsar. 相似文献
20.
F. A. Danevich O. V. Ivanov V. V. Kobychev V. I. Tretyak 《Kinematics and Physics of Celestial Bodies》2009,25(2):102-106
In a very conservative approach, supposing that all heat flow of the Earth is exclusively due to resonant capture inside the
Earth of axions emitted by 57Fe nuclei on Sun, we obtain limit on the mass of hadronic axion: m
a
< 1.8 keV. Taking into account release of heat from decays of 40K, 232Th, 238U inside the Earth, this estimation could be improved to the value: m
a
< 1.6 keV. Both the values are less restrictive than limits set in devoted experiments to search for 57Fe axions (m
a
< 216–745 eV), but are much better than limits obtained in experiments with 83Kr (m
a
< 5.5 keV) and 7Li (m
a
< 13.9–32 keV).
Published in Ukrainian in Kinematika i Fizika Nebesnykh Tel, 2009, Vol. 25, No. 2, pp. 143–149.
The article was translated by the authors. 相似文献