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1.
We determine lithium abundances in atmospheres of three carbon stars from synthetic spectrum fitting in the λλ 668–674 nm
range using the Li I λ 670.8 nm resonance doublet. To produce synthetic spectra, we use a modified list of atomic lines from
the VALD database and three alternative line lists of CN and C 2 molecules which are modifications of line lists from the Jorgensen’s website () and from the Kurucz database (1993, CD-ROM nos. 1–23). The spectral lines from these lists were tested by matching synthetic
spectra to observed spectra of the sun, Arcturus, and early R star HD 100764. We perform analysis of the blends involving
the Li I λ 670.8 nm doublet in spectra of N stars AW Cyg and UX Dra. The lithium abundances in HD 100764, AW Cyg, and UX Dra
are estimated to be lg N(Li) ≈ 2, −1.4, and −0.9, respectively. Discrepancies of lithium abundances lg N(Li) obtained with the help of molecular line lists do not seem to exceed 0.2 dex. 相似文献
2.
Measurements of the Doppler effect of the solar photosphere have been carried out at the Crimean Astrophysical Observatory
for 37 years, beginning in 1974 (in total, 2188 days or 13 247 h). The measurements use the differential center-to-limb method
of registration of line-of-sight velocity with a solar magnetograph (in the iron absorption line λ512.4 nm). As a result of
the experiment, two global pulsations of the sun with periods P
0 = 9600.606(12) and P
1 = 9597.936(16) s have been discovered. The nature of the periods is unknown. The first pulsation was detected in 1974–1982;
the second, during nearly all the 37 years. The 2008–2010 data confirm the stability of the initial phase of the P
1 pulsation with a mean (differential) amplitude of 0.25 m/s. The fact that the beat period of the two pulsations coincides
with the synodic period of Jupiter’s orbital revolution, i.e., 399 days, raises a new, complex problem for solar physics and
cosmogony. 相似文献
3.
The algorithm for determining effective optical thickness of absorption line formation in a plane-parallel homogeneous planetary
atmosphere is presented. The case of anisotropic scattering is considered. The results of numerical calculations of τ
e
(μ 0) at the scattering angle γ = π for some values of the single scattering albedo λ and the parameter of the Heyney-Greenstein
scattering indicatrix g are given. The refined equation for the function T
m
(−μ, μ 0) is presented. 相似文献
4.
Nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova remnants (SNRs) is used to investigate the properties
of Kepler’s SNR and, in particular, to predict the γ-eay spectrum expected from this SNR. Observations of the nonthermal radio and X-ray emission spectra as well as theoretical
constraints for the total supernova (SN) explosion energy E
sn are used to constrain the astronomical and particle acceleration parameters of the system. Under the assumption that Kepler’s
SN is a type Ia SN we determine for any given explosion energy E
sn and source distance d the mass density of the ambient interstellar medium (ISM) from a fit to the observed SNR size and expansion speed. This makes
it possible to make predictions for the expected γ-eay flux. Exploring the expected distance range we find that for a typical explosion energy E
sn=10 51 erg the expected energy flux of TeV γ-rays varies from 2×10 −11 to 10 −13 erg/(cm 2 s) when the distance changes from d=3.4 kpc to 7 kpc. In all cases the γ-eay emission is dominated by π
0-decay γ-rays due to nuclear CRs. Therefore Kepler’s SNR represents a very promising target for instruments like H.E.S.S., CANGAROO
and GLAST. A non-detection of γ-rays would mean that the actual source distance is larger than 7 kpc. 相似文献
5.
Stochastic temperatures and turbulence are characterized by average velocities u
th
and < u
turb
> ≡ u
0 and fluctuations u¢th {u'_{th}} and u′ (<u′ > = 0). Thus, the Doppler width of a line also has a fluctuating component Dl¢D \Delta {\lambda '_D} . Observed spectra correspond to the radiative flux averaged over time and over a star’s surface, <Hλ>. Usually, only the average velocities u
th
and u
0 are taken into account in photospheric models and these yield the Doppler width DlD(0) \Delta \lambda_D^{(0)} of a line in the customary way. The fluctuations Dl¢D \Delta {\lambda '_D} mean that near a line center the average absorption coefficient < αλ > is larger than the usual αλ, which depends only on the average velocities u
th
and u
0. This enhances the absorption line near the center and is not explained by the photospheric models. This new statistical
effect depends on the wavelength of the line. A comparison of observed lines with model profiles yields an estimate for the
average level of fluctuations in the Doppler width, h =
á | Dl¢D |
ñ | / |
DlD(0) \eta = {{{\left\langle {\left| {\Delta {{\lambda '}_D}} \right|} \right\rangle }} \left/ {{\Delta \lambda_D^{(0)}}} \right.} , which characterizes the average stochasticity of a photosphere and is important for understanding the physics of photospheres.
The depths of lines in synthetic spectra of stars are often greater than the observed values. The observed disagreement between
the theoretical and actually observed depths of lines can be corrected by introducing an additional parameter, the fluctuation
level η. Then it is possible to obtain estimates of η for a number of stars. 相似文献
6.
We present the condition of vanishing shear in a spatially homogeneous spacetime in terms of the Ricci rotation co-efficients
corresponding to an orthonormal tetrad ( ν
α.
A
η
α) (where ν
α is the unit vector along the time axis and
A
η
α are the three independent reciprocal group vectors). Assuming that the velocity vector can be expanded in the direction of ν
α and any one of the
A
η
α’s it is shown that shear-free motion is possible only in case of some special Bianchi types, and these cases are studied
assuming the velocity vector to be geodetic and that there may be a nonvanishing heat flux term. 相似文献
7.
In the spectral region λλ = 610.25−610.57 nm of the roAp star HD 101065, we performed the identification of the rare-earth
element absorption lines absent from the atomic spectral line databases VALD and DREAM. The identified lines were used for
calculating the synthetic spectra of the roAp stars HD 137949, HD 134214, and HD 24712. The upper limit of the identified
line estimates was determined. The rotation/pulsation parameter νsin i and magnetic field modulus were determined using the lines Nd III 669.083 nm and Ca I 616.217 nm. The element abundance in
the roAp stars HD 134214 and HD 24712 was determined for the first time using Nd III lines. Calculations were carried out
with the help of the code SynthM developed by S.A. Khan. 相似文献
8.
We calculated the variations of Rayleigh optical depth with changes of pressure and temperature for three observation sites:
Simferopol (φ = 44°57′N, λ = 34°8′E, h = 265 m above sea level), Nauchny (φ = 44°43′N, λ = 34°3′E, h = 583 m), and Ai-Petry meteorological station (φ = 44°24′N, λ = 34°6′E, h = 1180 m). 相似文献
9.
A gravity theory is considered with the Einstein-Hilbert Lagrangean R+ aR 2+ bR μν R μν , R μν being Ricci’s tensor and R the curvature scalar. The parameters a and b are taken of order 1 km 2. Arguments are given which suggest that the effective theory so obtained might be a fair approximation of a viable theory. A numerical integration is performed of the field equations for a free neutron gas. The result is that the star mass increases with increasing central density until about 1 solar mass and then decreases. The baryon number increases monotonically, which suggests that the theory allows stars in equilibrium with arbitrary baryon number, no matter how large. 相似文献
10.
The variability of the optical and X-ray fluxes from the binary GS 1826-238 is investigated. An epoch-folding analysis of
the optical data obtained with the RTT-150 telescope in 2003–2004 has revealed periodic brightness variations in the source
with a period P
orb = 2.24940 ± 0.00015 h with a high statistical significance. When estimating the detection significance of the periodic signal,
we have specially taken into account the presence of a powerful aperiodic component (“red noise”) in the source’s brightness
variability. The source’s power density spectra in the frequency range ∼10 −5–0.01 Hz have been obtained. We have detected a statistically significant break in the power density spectrum of GS 1826-238
at a frequency ν
br ≈ (8.48 ± 0.14) × 10 −5 Hz in both optical and X-ray energy bands. We have estimated the orbital period of the binary GS 1826-238 using the correlation
between the break frequency in the power density spectrum and the orbital period of binaries, P
orb ∝ 1/ ν
br, found by Gilfanov and Arefiev (2005): P
orb = 3.7 ± 0.8 h and P
orb = 11.3 ± 5.9 h when using Sco X-1 and 1H 16267-273, respectively, as reference sources. It seems to us that the method for
estimating the orbital periods of low-mass X-ray binaries using the correlation P
orb ∝ 1/ ν
br may turn out to be very promising, especially for persistent low-luminosity X-ray binaries. 相似文献
11.
We investigate the possibility of probing the large scale structure in the universe at large redshifts by studying fluctuations
in the redshifted 1420 MHz emission from the neutral hydrogen (HI) at early epochs. The neutral hydrogen content of the universe
is known from absorption studies for z ≲ 4.5. The HI distribution is expected to be inhomogeneous in the gravitational instability picture and this inhomogeneity leads to anisotropy
in the redshifted HI emission. The best hope of detecting this anisotropy is by using a large low-frequency interferometric
instrument like the Giant Meter-Wave Radio Telescope (GMRT). We calculate the visibility correlation function 〈V v(U) V v′(U)〉 at two frequencies i and v′ of the redshifted HI emission for an interferometric observation. In particular we give numerical results for the two GMRT channels centered around ν = 325 MHz and ν = 610 MHz from density inhomogeneity and peculiar velocity of the HI distribution. The visibility correlation is- 10 -10-10 -9 Jy 2. We calculate the signal-to-noise for detecting the correlation signal in the presence of system noise and show that the
GMRT might detect the signal for integration times - 100 hrs. We argue that the measurement of visibility correlation allows
optimal use of the uncorrelated nature of the system noise across baselines and frequency channels.
On leave from Harish-Chandra Research Institute, Chhatnag Road, Jhusi, Allahabad 211 019, India. 相似文献
12.
If cooled-down neutron stars have a thin atomic crystalline–iron crust, they must diffract X-rays of appropriate wavelength.
If the diffracted beam is to be visible from Earth (an extremely rare but possible situation), the illuminating source must
be very intense and near the reflecting star. An example is a binary system composed of two neutron stars in close orbit,
one of them inert, the other an X-ray pulsar. (Perhaps an “anomalous” X-ray pulsar or magnetar, not powered by gas absorption
from the companion or surrounding space, would be the cleanest example.) The observable to be searched for is a secondary
peak added (quasi-) periodically to the main X-ray pulse. The distinguishing feature of this secondary peak is that it appears
at wavelengths related by simple integer numbers, λ, λ/2, λ/3,…, λ/ n because of Bragg’s diffraction law. 相似文献
13.
Individual tidal torque λ
2, E
2 and apsidal-motion k
2 constants were calculated for 112 close eclipsing binaries ( CEBs) with Detached components belonging to the Main Sequence ( DMS-type) from the catalogue by Svechnikov and Perevozkina (Catalogue of orbital elements, masses and luminosities of variable
stars of DMS-type and some results of its statistical treatment, Ural State University Press, Yekaterinburg, pp. 1–5, 1999) and for 95 detached binaries taken from the catalogue by Torres et al. (Astron. Astrophys. Rev. 18:67, 2010) on the base of theoretical evolutionary stellar models including tidal torque constants by Claret (Astron. Astrophys. 424:919,
2004). A method of the inversion of model track grid into isochrones was formulated as a complex interpolation procedure for DMS-binaries
data. Sets of isochrones were computed in k
2– M, k
2– R, λ
2– M, λ
2– R, E
2– M, and E
2– R planes. Calculated tidal torque constants allow to test stellar structure theory by comparing observed and estimated values
of apsidal motion period and analyzing the correlation between timescales of synchronization, circularization, magnetic braking,
as well as nuclear burning of DMS-components. 相似文献
14.
For the case of Tycho’s supernova remnant (SNR) we present the relation between the blast wave and contact discontinuity radii
calculated within the nonlinear kinetic theory of cosmic ray (CR) acceleration in SNRs. It is demonstrated that these radii
are confirmed by recently published Chandra measurements which show that the observed contact discontinuity radius is so close
to the shock radius that it can only be explained by efficient CR acceleration which in turn makes the medium more compressible.
Together with the recently determined new value E
sn=1.2×10 51 erg of the SN explosion energy this also confirms our previous conclusion that a TeV γ-ray flux of (2–5)×10 −13 erg/(cm 2 s) is to be expected from Tycho’s SNR. Chandra measurements and the HEGRA upper limit of the TeV γ-ray flux together limit the source distance d to 3.3≤ d≤4 kpc. 相似文献
15.
It is shown (1) that the coefficients Ai of the limb darkening functions I(μ)/ Icenter = P5 (μ) = ∑ Ai μ i ( i = 0... 5; μ = cos ϑ), which had been published by Neckel and Labs ( Solar Phys. 153, 91, 1994), can well be approximated by analytical functions of wavelength λ, and (2) that at first sight purely formal extrapolation
of the functions P5(μ) to the very limb (μ = 0.0) is not meaningless: in combination with absolute intensities for the disk center these functions
yield ‘limb intensities’ which all correspond to almost the same ‘limb temperature’, Tlimb≈4746 K. Together these results lead to ‘reference functions’ which can quickly yield rather reliable values of the Sun's
continuum intensities, for any values of μ and λ. 相似文献
16.
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
∼ 10 4 cm −3. 相似文献
17.
There are relatively few H 2CO mappings of large-area giant molecular cloud (GMCs). H 2CO absorption lines are good tracers for low-temperature molecular clouds towards star formation regions. Thus, the aim of
the study was to identify H 2CO distributions in ambient molecular clouds. We investigated morphologic relations among 6-cm continuum brightness temperature
(CBT) data and H 2CO (1 11−1 10; Nanshan 25-m radio telescope), 12CO (1–0; 1.2-m CfA telescope) and midcourse space experiment (MSX) data, and considered the impact of background components
on foreground clouds. We report simultaneous 6-cm H 2CO absorption lines and H110 α radio recombination line observations and give several large-area mappings at 4.8 GHz toward W49 (50′×50′), W3 (70′×90′),
DR21/W75 (60′×90′) and NGC2024/NGC2023 (50′×100′) GMCs. By superimposing H 2CO and 12CO contours onto the MSX color map, we can compare correlations. The resolution for H 2CO, 12CO and MSX data was ∼10′, ∼8′ and ∼18.3″, respectively. Comparison of H 2CO and 12CO contours, 8.28-μm MSX colorscale and CBT data revealed great morphological correlation in the large area, although there
are some discrepancies between 12CO and H 2CO peaks in small areas. The NGC2024/NGC2023 GMC is a large area of HII regions with a high CBT, but a H 2CO cloud to the north is possible against the cosmic microwave background. A statistical diagram shows that 85.21% of H 2CO absorption lines are distributed in the intensity range from −1.0 to 0 Jy and the Δ V range from 1.206 to 5 km s −1. 相似文献
18.
Based on data for 102 OB3 stars with known proper motions and radial velocities, we have tested the distances derived by Megier
et al. from interstellar Ca II spectral lines. The internal reconciliation of the distance scales using the first derivative
of the angular velocity of Galactic rotation Ω′ 0 and the external reconciliation with Humphreys’s distance scale for OB associations refined by Mel’nik and Dambis show that
the initial distances should be reduced by ≈20%. Given this correction, the heliocentric distances of these stars lie within
the range 0.6–2.6 kpc. A kinematic analysis of these stars at a fixed Galactocentric distance of the Sun, R
0 = 8 kpc, has allowed the following parameters to be determined: (1) the solar peculiar velocity components ( u
⊙, v
⊙, ω
⊙) = (8.9, 10.3, 6.8) ± (0.6, 1.0, 0.4) km s −1; (2) the Galactic rotation parameters Ω 0 = −31.5 ± 0.9 km s −1 kpc −1, Ω′ 0 = +4.49 ± 0.12 km s −1 kpc −2, Ω″ 0 = −1.05 ± 0.38 km s −1 kpc −3 (the corresponding Oort constants are A = 17.9 ± 0.5 km s −1 kpc −1, B = −13.6 ± 1.0 km s −1 kpc −1 and the circular rotation velocity of the solar neighborhood is | V
0| = 252 ± 14 km s −1); (3) the spiral density wave parameters, namely: the perturbation amplitudes for the radial and azimuthal velocity components,
respectively, f
R
= −12.5±1.1 km s −1 and f
ϑ
= 2.0 ± 1.6 km s −1; the pitch angle for the two-armed spiral pattern i = −5.3° ± 0.3°, with the wavelength of the spiral density wave at the solar distance being λ = 2.3 ± 0.2 kpc; the Sun’s phase in the spiral wave x
⊙ = −91° ± 4°. 相似文献
19.
In the problem of 2+2 bodies in the Robe’s setup, one of the primaries of mass m*1m^{*}_{1} is a rigid spherical shell filled with a homogeneous incompressible fluid of density ρ
1. The second primary is a mass point m
2 outside the shell. The third and the fourth bodies (of mass m
3 and m
4 respectively) are small solid spheres of density ρ
3 and ρ
4 respectively inside the shell, with the assumption that the mass and the radius of third and fourth body are infinitesimal.
We assume m
2 is describing a circle around m*1m^{*}_{1}. The masses m
3 and m
4 mutually attract each other, do not influence the motion of m*1m^{*}_{1} and m
2 but are influenced by them. We also assume masses m
3 and m
4 are moving in the plane of motion of mass m
2. In the paper, the equations of motion, equilibrium solutions, linear stability of m
3 and m
4 are analyzed. There are four collinear equilibrium solutions for the given system. The collinear equilibrium solutions are
unstable for all values of the mass parameters μ, μ
3, μ
4. There exist an infinite number of non collinear equilibrium solutions each for m
3 and m
4, lying on circles of radii λ, λ′ respectively (if the densities of m
3 and m
4 are different) and the centre at the second primary. These solutions are also unstable for all values of the parameters μ, μ
3, μ
4, φ, φ′. Such a model may be useful to study the motion of submarines due to the attraction of earth and moon. 相似文献
20.
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
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