共查询到20条相似文献，搜索用时 15 毫秒
1.
S. G. Sichevskij 《Astrophysical Bulletin》2017,72(2):141-149
We describe Bayesian probabilistic approach to estimating the properties of stars and the interstellar extinction law based on photometric observations and using prior data about the parameters of the stars. The accuracy of the resulting estimates is analyzed in the case of SDSS and 2MASS surveys. We found that our estimates have no systematic deviations in the case of photometric accuracy typical of the surveys considered and errors of prior data of ΔT eff = ±150 K and Δlog g = ±0.5. Note that the error of the estimated interstellar extinction A 0 is of about 0. m 3, and the error of the R 0 estimate depends on extinction and is close 0.2 for moderate A0 values. The fractional error of the estimated stellar angular diameters is close to 10%. A possible application of our approach is to determine the dependence of interstellar extinction on distance using stars closely located in the same sky area. 相似文献
2.
The X-ray spectrum of the Crab nebula has been determined in the energy range 0.5 10 keV using thin window proportional counters carried aboard a Centaur IIA rocket launched from TERLS, India. The spectrum can be well represented by a power law with an exponent?2.1 beyond 2 keV. The absorption of the soft X-ray component below 2 keV is clearly seen in the experiment. Attempts to understand quantitatively the spectral features in terms of interstellar absorption lead to a column density of hydrogen in the iirection of the Crab nebula of 3.5×1021 H atoms cm?2, if we adopt a revised version of the interstellar absorption coefficients of Brown and Gould to include the contributions of heavier elements, especially of iron. This value of density is a factor of 2 higher than the density obtained from 21 cm radio observations, but falls well within the range of values for atomic and total hydrogen deducible from UV measurements with satellites and the measured visual extinction coefficients for the Crab nebula. It is concluded that it is not necessary to consider anomalous abundance of elements like carbon or neon either in the source or in the interstellar medium as suggested by some authors. The absorption of X-rays in the interstellar dust in the light of current dust models is presented. 相似文献
3.
We have measured the interstellar extinction in the region of ultradeep Galactic-field observations by the Chandra telescope (l II, b II) ≈ 0.1–1.42 using photometric data from the 2MASS infrared allsky survey. The angular resolution of our interstellar extinction map is 1′.8. We show that the interstellar extinction has a minimum, A V ～ 3.4, near the center of the Chandra field of view and increases to A V ～ 5.8–6 at the edge of the field of view. In addition, we show that the bulk of the extinction is gained in the Galactic disk and is approximately the same for all bulge stars. Our results will be subsequently used to process the Chandra data and to estimate the properties of the stellar population in this region. 相似文献
4.
Lindsey F. Smith 《Astrophysics and Space Science》1975,34(1):49-55
The upper limit for the absorption cross section σ H ext , of dust in Hii regions in the wave-length range 912–504 Å derived by Mezgeret al. (1974), is compatible with that expected for large dust grains, and a gas-to-dust ratio equal to that in the general interstellar medium. The albedo of the small grains must be high for λ>504 Å. This restriction is lifted if the visual extinction cross section of the grains in Hii regions is less than that for grains in the general interstellar medium. New observations of the Orion Nebula indicate that the visual extinction cross section is within a factor 2 of the value in the general interstellar medium. 相似文献
5.
Using the discrete dipole approximation, we have calculated the extinction efficiency of hollow spherical particles of graphite as a possible constituent of interstellar grains. The particles had a shell structure with the basal plane perpendicular to the radius. The calculations were made on the particles having the outer radiusR
0=10 and 5nm in the wave number region from 0.8 to 8.0 m–1 using the anisotropic optical constants. It was found that the hollow particles with the inner radiusR
10.65R
0 yield an extinction feature at 4.6 m–1, which fits fairly well to one observed in the interstellar extinction. 相似文献
6.
W. W. Duley 《Astrophysics and Space Science》1983,92(1):45-51
Laboratory data on the spectra of CO adsorbed on small MgO particles show that CO absorption leads to a weakening of the 220 nm band together with a shift of this band to shorter wavelengths. CO adsorption also results in the formation of a cyclic CO carbon ion that absorbs at 2.15 m–1. It is shown that this band provides a close match to a major component of the very broad structure seen in interstellar extinction at the same energy. Effects of CO adsorption on the 220 nm band and VUV extinction are discussed in light of recent observational data on stars with peculiar extinction curves. 相似文献
7.
W. W. Duley 《Astrophysics and Space Science》1982,88(2):501-505
Twenty-eight of the thirty-nine diffuse interstellar bands identified by Herbig (1975) are shown to constitute three vibronic systems with origins at 14 321, 15 153, and 15 343 cm–1 (vac). Structure within these three systems arises from the excitation of vibrational modes withv
1=275 cm–1,v
2=445.5 cm–1, andv
3=793 cm–1. The electronic origins at 14 321 and 15 343 cm–1 correspond to narrow lines observed in the spectrum of Cr3+ ions at cubic sites in MgO solids while the 15 153 cm–1 origin arises in Mn4+ : MgO. Hence, many of the diffuse bands in the visible likely are due to small MgO particles containing these ions. This observation is compatible with recent experimental data showing broad bands at 160 nm and 220 nm from finely divided MgO solids that match features in the interstellar extinction curve. 相似文献
8.
J. C. Brown V. A. Carlaw T. V. Cawthorne V. Icke 《Astrophysics and Space Science》1988,143(1):153-161
The jet/grain model proposed by Ramatyet al. (1984, hereafter abbreviated as RKL) for production of the narrow gamma-ray lines reported from SS433 is examined and shown to be untenable on numerous grounds. Most importantly:
- The huge Coulomb collisional losses (W c?2×1041 erg s?1) from the jet, which would necessarily accompany non-thermal production of the gamma rays, demands a jet acceleration/collimation process acting over a very long range and with a power at least 102 times the Eddington limit for any stellar object.
- There is a collisional thick target limit (irrespective of jet mass) to the gamma ray yield per interstellar proton. Consequently, the gamma-ray data demand an improbably high interstellar density (?109 cm?3).
- For the grains to be kept cool enough (?3000 K) to survive the heating rateW c either by radiation or jet expansion would demand a ‘jet’ wider than its length and so inconsistent with narrow lines. In the case of radiative cooling, the resultant IR flux would exceed the observed values by a factor ?104.
- Light scattered on the jet grain mass required would be highly polarized, contrary to observations, unless the jet was optically thick to grains, again precluding their radiative cooling.
- To avoid unacceptable precessional broadening of the gamma-ray lines demands an emitting jet length ?0.5 days atv=0.26c. This increases the necessary mass loss rate by a factor ?10 over the values obtained by RKL who assumed a 4-day ‘flare’.
- The model also predicts rest energy gamma-ray lines which are not observed.
9.
We discuss in this paper the possibility of interpreting the 2200 Å band occurring in the interstellar extinction curves as being attributed to porous graphite. The results show that grains with radii smaller than 0.015 m and a porosity degree within the values 0.02f0.25 are able to fit satisfactorily the peak at 4.6 m–1 and the band shape between 4 and 5.2 m–1. Consideration of the expected density for such particles seems to confirm that interstellar grains may be porous but, at the same time, suggests that care must be taken when data concerning dust in the solar system are extrapolated to the interstellar space. 相似文献
10.
Based on the Gaia DR1 TGAS parallaxes and photometry from the Tycho-2, Gaia, 2MASS, andWISE catalogues, we have produced a sample of ~100 000 clump red giants within ~800 pc of the Sun. The systematic variations of the mode of their absolute magnitude as a function of the distance, magnitude, and other parameters have been analyzed. We show that these variations reach 0.7 mag and cannot be explained by variations in the interstellar extinction or intrinsic properties of stars and by selection. The only explanation seems to be a systematic error of the Gaia DR1 TGAS parallax dependent on the square of the observed distance in kpc: 0.18R 2 mas. Allowance for this error reduces significantly the systematic dependences of the absolute magnitude mode on all parameters. This error reaches 0.1 mas within 800 pc of the Sun and allows an upper limit for the accuracy of the TGAS parallaxes to be estimated as 0.2 mas. A careful allowance for such errors is needed to use clump red giants as “standard candles.” This eliminates all discrepancies between the theoretical and empirical estimates of the characteristics of these stars and allows us to obtain the first estimates of the modes of their absolute magnitudes from the Gaia parallaxes: mode(M H ) = ?1.49 m ± 0.04 m , mode(M Ks ) = ?1.63 m ± 0.03 m , mode(M W1) = ?1.67 m ± 0.05 m mode(M W2) = ?1.67 m ± 0.05 m , mode(M W3) = ?1.66 m ± 0.02 m , mode(M W4) = ?1.73 m ± 0.03 m , as well as the corresponding estimates of their de-reddened colors. 相似文献
11.
Parallaxes with an accuracy better than 10% and proper motions from the Gaia DR1 TGAS catalogue, radial velocities from the Pulkovo Compilation of Radial Velocities (PCRV), accurate Tycho-2 photometry, theoretical PARSEC, MIST, YaPSI, BaSTI isochrones, and the most accurate reddening and interstellar extinction estimates have been used to analyze the kinematics of 9543 thin-disk B-F stars as a function of their dereddened color. The stars under consideration are located on the Hertzsprung–Russell diagram relative to the isochrones with an accuracy of a few hundredths of a magnitude, i.e., at the level of uncertainty in the parallax, photometry, reddening, extinction, and the isochrones themselves. This has allowed us to choose the most plausible reddening and extinction estimates and to conclude that the reddening and extinction were significantly underestimated in some kinematic studies of other authors. Owing to the higher accuracy of TGAS parallaxes than that of Hipparcos ones, the median accuracy of the velocity components U, V, W in this study has improved to 1.7 km s?1, although outside the range ?0.1 m < (B T ? V T )0 < 0.5 m the kinematic characteristics are noticeably biased due to the incompleteness of the sample. We have confirmed the variations in the mean velocity of stars relative to the Sun and the stellar velocity dispersion as a function of their dereddened color known from the Hipparcos data. Given the age estimates for the stars under consideration from the TRILEGAL model and the Geneva–Copenhagen survey, these variations may be considered as variations as a function of the stellar age. A comparison of our results with the results of other studies of the stellar kinematics near the Sun has shown that selection and reddening underestimation explain almost completely the discrepancies between the results. The dispersions and mean velocities from the results of reliable studies fit into a ±2 km s?1 corridor, while the ratios σ V /σ U and σ W /σ U fit into ±0.05. Based on all reliable studies in the range ?0.1 m < (B T ? V T )0 < 0.5m, i.e., for an age from 0.23 to 2.4 Gyr, we have found: W⊙ = 7.15 km s?1, \({\sigma _U} = 16.0{e^{1.29({B_T} - {V_T})o}}\), \({\sigma _V} = 10.9{e^{1.11({B_T} - {V_T})o}}\), \({\sigma _W} = 6.8{e^{1.46({B_T} - {V_T})o}}\), the stellar velocity dispersions in km s?1 are proportional to the age in Gyr raised to the power β U = 0.33, β V = 0.285, and β W = 0.37. 相似文献
12.
Data on interstellar extinction are interpreted to imply an identification of interstellar grains with naturally freeze-dried bacteria and algae. The total mass of such bacterial and algal cells in the galaxy is enormous, 1040 g. The identification is based on Mie scattering calculations for an experimentally determined size distribution of bacteria. Agreement between our model calculations and astronomical data is remarkably precise over the wavelength intervals µ–1 < ;–2 < 1.94µ–1 and 2.5µ–1 < ;–1 < 3.0 ;–1. Over the more restricted waveband 4000–5000 Å an excess interstellar absorption is found which is in uncannily close agreement with the absorption properties of phytoplankton pigments. The strongest of the diffuse interstellar bands are provisionally assingned to carotenoid-chlorophyll pigment complexes such as exist in algae and pigmented bacteria. The 2200 Å interstellar absorption feature could be due to degraded cellulose strands which form spherical graphitic particles, but could equally well be due to protein-lipid-nucleic acid complexes in bacteria and viruses. Interstellar extinction at wavelengths <1800 Å could be due to scattering by virus particles. 相似文献
13.
This paper reviews the electric field environment of the Moon. Lunar surface electric potentials are reported as follows: Solar Wind - Dayside: øo + 10 to + 18 V Solar Wind - Terminator: øo ç ? 10 to ? 100 V Electron and ion densities in the plasma sheath adjacent to each surface potential regime are evaluated and the corresponding Debye length estimated. The electric fields are then approximated by the surface potential over the Debye length. The results are: Solar Wind - Dayside: Eo ? 10 V m?1 outward Solar Wind - Terminator: Eo ç 1 to 10 V m?1 inward These fields are all at least 3 orders of magnitude higher than the pervasive solar wind electric field; however they are confined to within a few tens of meters of the lunar surface. 相似文献
14.
Data on interstellar extinction are interpreted to imply an identification of interstellar grains with naturally freeze-dried bacteria and algae. The total mass of such bacterial and algal cells in the galaxy is enormous, ～ 1040 g. The identification is based on Mie scattering calculations for an experimentally determined size distribution of bacteria. Agreement between our model calculations and astronomical data is remarkably precise over the wavelength intervals 1 μ-1 < λ-1 < 1.94 μ-1and 2.5 μ-1 < λ-1 < 3.0 μ-1. Over the more restricted waveband 4000–5000 Å an excess interstellar absorption is found which is in uncannily close agreement with the absorption properties of phytoplankton pigments. The strongest of the diffuse interstellar bands are provisionally assigned to carotenoid-chlorophyll pigment complexes such as exist in algae and pigmented bacteria. The λ2200 Å interstellar absorption feature could be due to `degraded' cellulose strands which form spherical graphitic particles, but could equally well be due to protein-lipid-nucleic acid complexes in bacteria and viruses. Interstellar extinction at wavelengths λ < 1800 Å could be due to scattering by virus particles. 相似文献
15.
E. I. Tetruashvili 《Solar physics》1974,39(2):387-391
Coronal yellow line emission was observed by the Lyot coronagraph at the Abastumani Astrophysical Observatory. Line intensity is I = 45 erg cm?2 s?1 sr?1 Å?1, its half-width Δλ = 1.3 Å, electronconcentration n e = 7.5 × 109 cm?3. 相似文献
16.
Based on the material of multiple high-resolution R = 60 000 observations conducted on the 6-m telescope (BTA) of the Special Astrophysical Observatory in combination with the Nasmyth Echelle Spectrograph (NES), we closely studied the features of the optical spectrum of the star MWC17 with the B[e] phenomenon. In the wavelength interval of 4050–6750 Å, we identified numerous permitted and forbidden emissions, interstellar Na I lines, and diffuse interstellar bands (DIBs). Radial velocities were estimated from lines of different origin. As the systemic velocity, Vsys, the velocity of the forbidden emissions can be accepted: ?47 kms?1 (relative to the local standard Vlsr = ?42 kms?1). Comparison of the obtained data with the earlier measurements allows us to conclude on the absence of considerable variability of spectral details. 相似文献
17.
Macroscopic equations of motion are used to derive several forms of the generalized Ohm's law for partially ionized ternary gases in magnetic fields, and a conductivity σ is defined that is independent of the magnetic field. A flux theorem is derived using a velocityu H that can be defined to be the velocity of magnetic field lines;u H is only slightly different from the velocity of the electron component of the gas. It is shown that σ is the conductivity relevant to the decay of magnetic flux through any surface moving everywhere with velocityu H . The rate of increase of the thermal energy density of the gas arising through collisions between particles of different species can be resolved into Joule heating at the ratej 2/σ, wherej is the current density, and heating associated with ambipolar drift. The latter, contrary to what has been claimed by some authors, is not necessarily fully compensated by a decrease in the energy of the electromagnetic field. In many applications such compensation does occur, but it may not in interstellar clouds where large amounts of gravitational energy can be made available by collapse, and then both heating and an increase in electromagnetic field energy may occur. 相似文献
18.
S. G. Sichevskij 《Astrophysical Bulletin》2018,73(1):98-107
The feasibility of the determination of the physical conditions in star’s atmosphere and the parameters of interstellar extinction from broad-band photometric observations in the 300–3000 nm wavelength interval is studied using SDSS and 2MASS data. The photometric accuracy of these surveys is shown to be insufficient for achieving in practice the theoretical possibility of estimating the atmospheric parameters of stars based on ugriz and JHKs photometry exclusively because such determinations result in correlations between the temperature and extinction estimates. The uncertainty of interstellar extinction estimates can be reduced if prior data about the temperature are available. The surveys considered can nevertheless be potentially valuable sources of information about both stellar atmospheric parameters and the interstellar medium. 相似文献
19.
20.
Donald F. Neidig 《Solar physics》1983,85(2):285-302
Spectrograph and multiple-band polarimeter observations of the 24 April 1981 white-light flare indicate the presence of an optical continuum with intensity increasing strongly below 4000 Å. The flare emission (lines and continuum combined) is unpolarized and, at 3600 Å, exceeds the brightness of the background solar surface by 360%. Analysis of the spectrum between 3600 and 8200 Å, at a location three arc sec from the brightest point in the kernel, yields a probable temperature of 6700 K for the continuum emitting layer. The wavelength dependence of the continuum indicates emission by both negative hydrogen (H?) and Balmer continuum, with the H? probably originating in the upper photosphere at a height (above τ5000 Å = 1) in the range 200–300 km. Analysis of the Balmer lines and continuum yields an electron density 5.3 × 1013 cm?3 and a second-level hydrogen column density 1.1 × 1016 cm?2. The peak radiative output integrated over wavelength is 6.1 × 1027 erg s?1. The observed continuum intensity, if originating at a height of 300 km, implies an energy loss rate of 103 erg s?1 cm?3. 相似文献