共查询到20条相似文献，搜索用时 500 毫秒
1.
2.
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
3.
In the present paper various observational data are used to compare seven most common models proposed to describe the behaviour
of the interstellar extinction in different parts of the sky. The data for field stars, open and globular clusters are used
to select the most adequate model at different distances and for different directions in the Galaxy. The results of this study
allow to select the best models for particular distances and directions. They also make it possible to propose a synthesized
model describing the interstellar extinction.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
Joy Heckathorn 《Astrophysics and Space Science》1971,11(2):309-321
The observational data for planetary nebulae in the radio region of the spectrum is reviewed and summarized. The methods of determining interstellar extinction, electron temperatures and turnover points in the spectrum from these observations are given, as are the tests for the recombination theory and a discussion of the validity of several models of these objects. 相似文献
5.
W. W. Duley 《Astrophysics and Space Science》1981,78(1):145-156
The production of discrete line and broad-band extinction by small interstellar oxide and silicate particles is discussed
quantitatively. Restrictions on particle size and refractive index that are required to produce ‘pure’ absorption features
are reviewed. The relationship between optical depth in interstellar extinction and absorption coefficients for bulk materials
is used to reach some general conclusions concerning the diffuse interstellar features, VUV extinction and the composition
of interstellar dust. It is noted that charge transfer bands of ions such as Fe3+ may be detectable in the VUV spectrum of dust. Several effects that lead to the enhancement of oscillator strength by 103–104 in small particles are discussed. 相似文献
6.
Profiles of the 4430 band are calculated for resonant absorbers distributed within graphite particles, silicate particles and solid H2 grains. The sizes of grains adopted are those which give agreement with the interstellar extinction. Only in the latter two cases can satisfactory agreement be obtained with recent observational data. 相似文献
7.
F. Zagury 《Astronomische Nachrichten》2013,334(10):1107-1114
The 2200 Å bump is a major figure of interstellar extinction. However, extinction curves with no bump exist and are, with no exception, linear from the near‐infrared down to 2500 Å at least, often over all the visible‐UV spectrum. The duality linear versus bump‐like extinction curves can be used to re‐investigate the relationship between the bump and the continuum of interstellar extinction, and answer questions as why do we observe two different kinds of extinction (linear or with a bump) in interstellar clouds? How are they related? How does the existence of two different extinction laws fits with the requirement that extinction curves depend exclusively on the reddening E (B – V) and on a single additional parameter? What is this free parameter? It will be found that (1) interstellar dust models, which suppose the existence of three different types of particles, each contributing to the extinction in a specific wavelength range, fail to account for the observations; (2) the 2200 Å bump is very unlikely to be absorption by some yet unidentified molecule; (3) the true law of interstellar extinction must be linear from the visible to the far‐UV, and is the same for all directions including other galaxies (as the Magellanic Clouds). In extinction curves with a bump the excess of starlight (or the lack of extinction) observed at wavelengths less than λ = 4000 Å arises from a large contribution of light scattered by hydrogen on the line of sight. Although counter‐intuitive this contribution is predicted by theory. The free parameter of interstellar extinction is related to distances between the observer, the cloud on the line of sight, and the star behind it (the parameter is likely to be the ratio of the distances from the cloud to the star and to the observer). The continuum of the extinction curve and the bump contain no information on the chemical composition of interstellar clouds. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
8.
We investigate UV and optical spectra of a sample of nearby early-type galaxies with evidence of nuclear line emission. The
spectral signatures of various contributors to the UV, such as the interstellar medium and various stellar populations are
analyzed and compared with the optical spectral properties. We discuss the impact of these effects on the observational properties
of galaxy evolution.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
9.
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
10.
W. W. Duley 《Astrophysics and Space Science》1977,47(1):185-193
Evidence is presented that zero phonon lines of defect centres in MgO and CaO are responsible for the diffuse interstellar bands at 5362, 5705, 6425.7, and 6699.4 Å. Phonon sidebands of these lines are identified with the diffuse bands at 5535, 6177, 6196, 6284, and 6314 Å. These features arise in interstellar MgO and CaO particles with sizes 50 Å. Infrared spectral features due to interstellar MgO and CaO are discussed. 相似文献
11.
Silvia Casu Cesare Cecchi-Pestellini Santi Aiello 《Monthly notices of the Royal Astronomical Society》2001,325(2):826-834
Dust grains respond to the physical and chemical conditions of the interstellar region in which they are embedded. The interaction produces an extinction curve which depends on the local environment and on the past history of the dust grains. In this work we present a theoretical study of the effects of radial variations of dust extinction properties on gas-phase chemistry in spherical core–halo clouds. We use observational constraints on the variation range of the extinction curve, and we analyse if the degree of dust environmental processing could be reflected by chemical signatures in the gas-phase molecular concentrations. The results of this work show that significant variations in the photodestruction rates and in the thermal profile of the cloud might induce chemical patterns otherwise excluded in the standard dense-cloud chemistry. Some discrepancies between observations and theoretical provisions are discussed in the light of the present results. 相似文献
12.
The observed features of the interstellar extinction curve in both the Galaxy and in the external galaxies LMC and SMC are explained on the basis of a model involving clumps of hollow or porous organic particles with an overall volume filling factor of 0.1. The hollow organic particles have a ready explanation in terms of the bacterial grain model. The visual and near infrared observations of extinction are fitted by a size distribution of such aggregates similar to the distribution law discovered for the larger grains in Halley's comet, but with a cutoff at low radii taken at 0.5 m for the Galaxy and 0.3 and 0.4 , respectively, for SMC and LMC. Fine tuning of the theoretical extinction curve to fit observational data in the ultraviolet involves variable contributions from small condensed polymeric units of typical radius 0.012 m and graphite particles of radii 0.02 . These particle species may be regarded as being derived from the primary distribution of clumps. The implication is that cometary sources could provide a major component of the grains in interstellar space. 相似文献
13.
Correlation patterns between 11 diffuse interstellar bands and ultraviolet extinction 总被引：1，自引：0，他引：1
A. Megier J. Kre&#;owski T. Weselak 《Monthly notices of the Royal Astronomical Society》2005,358(2):563-571
We relate the equivalent widths of 11 diffuse interstellar bands, measured in the spectra of 49 stars, to different colour excesses in the ultraviolet. We find that most of the observed bands correlate positively with the extinction in the neighbourhood of the 2175-Å bump. Correlation with colour excesses in other parts of the extinction curve is more variable from one diffuse interstellar band to another; we find that some diffuse bands (5797, 5850 and 6376 Å) correlate positively with the overall slope of the extinction curve, while others (5780 and 6284 Å) exhibit negative correlation. We discuss the implications of these results on the links between the diffuse interstellar band carriers and the properties of the interstellar grains. 相似文献
14.
We investigate the plausibility of using diffuse interstellar band at862 nm for tracing interstellar extinction with the ESA's
astrometric space mission GAIA. For this purpose we perform numerical tests to simulate the conditions of real observations,
covering a wide range of stellar parameters and different amounts of interstellar extinction. Our simulations indicate that
with the present Radial Velocity Spectrometer setup the uncertainty in color excess of σE(B-V)≤ 0.05 can be achieved only for the interstellar reddening tracers brighter than V ∼ 13. None of the plausible tracers can provide accurate color excesses (σ
E(B-V)
≤ 0.05) at the distances beyond 2 kpc. We therefore conclude that with the currently planned instrumentation onboard GAIA
this method can not be used as a stand-alone approach for probing interstellar extinction on the Galactic distance scales
within the framework of the GAIA mission.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
We have calculated the extinction efficiencies of randomly oriented infinite graphite cylinders, including hollow cylinders, using the rigorous Kerker-Matijevi formulae. The peak in the mid-ultraviolet extinction varies in wavelength with particle radius and cavity size in a way that makes such particles of limited interest as models of interstellar grains. 相似文献
16.
We deduce the mass distribution and total mass density of interstellar dust streaming into the solar system and compare the
results to the conditions of the very local interstellar medium (VLISM). The mass distribution derived from in situ measurements
shows a gentler slope and includes larger grains, compared to a model distribution proposed for the wavelength dependence
of the interstellar extinction. The mass density of grains in the solar system is consistent with that expected from measurements
of the visible interstellar extinction and the abundance constraints of elements in the diffuse interstellar medium (ISM),
instead of those in the VLISM. This may imply that interstellar dust grains are not associated with the VLISM and that the
conditions of the grains are better represented by the ones expected in the diffuse ISM. If this is the case, then the flatter
slope in the mass distribution and the detection of larger interstellar grains in the solar system may even indicate that
coagulation growth of dust in the diffuse ISM is more effective than previously inferred.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
From the data on bright stars of different spectral and luminosity classes from the 13-color photometry catalog, the selective extinction of light by the interstellar dust has been studied. The stars from the 1000-pc vicinity of the Sun were investigated. In the optical spectral range, the interstellar extinction curves show systematic deviations from the “λ?1” law, which allows one to sort them into three types. The observed curves of the interstellar dust extinction were compared with the theoretical curves calculated from the reflectance spectra of the asteroids under the approximation of the Rayleigh particles. The calculated extinction curves for the surface material of D-type asteroids and the Tagish Lake carbonaceous chondrite agree rather well with the observed curves of the interstellar extinction of the first type. 相似文献
18.
D A Williams 《Astrophysics and Space Science》1996,237(1-2):243-266
Our present knowledge of the diffuse interstellar bands (two of which were first noted by Wilson in 1958) is briefly summarized.
Other broad and very broad interstellar features (the 220nm extinction bump, the very broad structure in the extinction curve,
the extended red emission in reflection and other nebulae, and the unidentified-sometimes called the “overidentified”-infrared
bands) are also briefly described. The origins of all these features remain unknown, in spite of intensive study. Possible
relations between these various features and families is briefly discussed. Recent observations are shown to support the hypothesis
that the carriers of the diffuse bands are free-flying molecules, whereas the alternative hypothesis of dust grains now seems
to be untenable. Candidate types of molecular carriers are mentioned, and the possible source of such molecules in the diffuse
interstellar medium is briefly discussed. 相似文献
19.
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
20.
In a recent paper Millar has shown that if one assumes that the carbon depleted from the gas phase is all tied up into small graphite grains the observational data raise serious doubts against the hypothesis that these particles are responsible for the 2200 Å extinction hump. In the present paper it is shown that this problem may be overcome if the presence in the interstellar space of graphite grains with sizes greater than 0.02 is taken into account. The derived ratios between the masses of large grains, which do not contribute to the ultraviolet extinction hump, and those of the small ones varies from region to region of the sky and are consistent with those evaluated in the circumstellar shells of carbon stars. Moreover, the largest sizes of the graphite particles we find are in agreement with those needed to fit the interstellar extinction curve over the wavelength range 0.11–<1 . 相似文献