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1.
The colour difference between the star and the attendant reflection nebula and polarization both caused by silicate and graphite grains have been given. The properly normalized size distribution function for each type of grains has been considered within homogeneous plane parallel slab-model of the reflection nebula with the star in the rear. Contrary to some earlier results, it has been possible to show that silicate grains can certainly play a role in the phenomena of reflection nebulae.  相似文献   

2.
Lynds 1199 is an extended dark cloud of moderate opacity in the upper Cepheus region. The B3V type star HD206135 illuminating the reflection nebula DG 175 is associated with this cloud. In this paper the nature of the cloud and its associated young stellar objects is studied on the basis of13CO data obtained with the 4 m millimeter wave telescope of Nagoya University, photographic observations taken with the 60/90 cm Schmidt telescope of Konkoly Observatory, as well as IRAS data.  相似文献   

3.
We report the discovery of the first probable Galactic [WN] central star of a planetary nebula (CSPN). The planetary nebula candidate was found during our systematic scans of the AAO/UKST Hα Survey of the Milky Way. Subsequent confirmatory spectroscopy of the nebula and central star reveals the remarkable nature of this object. The nebular spectrum shows emission lines with large expansion velocities exceeding 150 km s−1, suggesting that perhaps the object is not a conventional planetary nebula. The central star itself is very red and is identified as being of the [WN] class, which makes it unique in the Galaxy. A large body of supplementary observational data supports the hypothesis that this object is indeed a planetary nebula and not a Population I Wolf–Rayet star with a ring nebula.  相似文献   

4.
The possible occurrence of luminescence emission by different irradiated materials in interstellar space is discussed. It is shown by means of a model computation that the quantum efficiency of luminescence emission is high enough and can, in general, be detected in interstellar space. Further, it is argued that the wavelength-dependent intensity increase observed in the NGC 7023 reflection nebula at the distance of 3.4 from the illuminating star can be explained by luminescence emission of UV irradiated and Cu or rare-earth-doped glassy particles.  相似文献   

5.
Near-infrared linear imaging polarimetry of the young stellar objects R CrA and T CrA in the J , H and K n bands, and circular imaging polarimetry in the H band, is presented. The data are modelled with the Clark and McCall scattering model. The R CrA and T CrA system is shown to be a particularly complex scattering environment. In the case of R CrA there is evidence that the wavelength dependence of polarization changes across the nebula. MRN dust grain models do not explain this behaviour. Depolarization by line emission is considered as an alternative explanation. The dust grain properties could also be changing across the nebula.
Although surrounded by reflection nebulosity, there is a region of particularly low polarization surrounding R CrA that is best modelled by the canonical bipolar outflow being truncated by an evacuated spherical cavity surrounding the star. The symmetry axis of the nebula appears inclined by 50° to the plane of the sky.
The H -band circular polarimetry of R CrA clearly shows a quadrupolar structure of positive and negative degrees of circular polarization that reach peak magnitudes of ∼5 per cent within our limited map. It is shown that spherical MRN grains are incapable of producing this circular polarization given the observed linear polarization of the R CrA system. Instead, scattering from aligned non-spherical grains is proposed as the operating mechanism.
T CrA is a more archetypical bipolar reflection nebula, and this object is modelled as a canonical parabolic reflection nebula that lies in the plane of the sky. The wavelength independence of linear polarization in the T CrA reflection nebula suggests that the scattering particles are Rayleigh sized. This is modelled with the MRN interstellar grain size distribution.  相似文献   

6.
We have developed a model for reflection nebulae around luminous infrared sources embedded in dense dust clouds. The aim of this study is to determine the sizes of the scattering grains. In our analysis, we have adopted an MRN-like power-law size distribution (Mathis, Rumpl, and Nordsieck) of graphite and silicate grains, but other current dust models would give results which were substantially the same. In the optically thin limit, the intensity of the scattered light is proportional to the dust column density, while in the optically thick limit, it reflects the grain albedo. The results show that the shape of the infrared spectrum is the result of a combination of the scattering properties of the dust, the spectrum of the illuminating source, and foreground extinction, while geometry plays a minor role. Comparison of our model results with infrared observations of the reflection nebula surrounding OMC-2/IRS 1 shows that either a grain size distribution like that found in the diffuse interstellar medium, or one consisting of larger grains, can explain the observed shape of the spectrum. However, the absolute intensity level of the scattered light, as well as the observed polarization, requires large grains (approximately 5000 angstroms). By adding water ice mantles to the silicate and graphite cores, we have modeled the 3.08 micrometers ice band feature, which has been observed in the spectra of several infrared reflection nebulae. We show that this ice band arises naturally in optically thick reflection nebulae containing ice-coated grains. We show that the shape of the ice band is diagnostic of the presence of large grains, as previously suggested by Knacke and McCorkle. Comparison with observations of the BN/KL reflection nebula in the OMC-1 cloud shows that large ice grains (approximately 5000 angstroms) contribute substantially to the scattered light.  相似文献   

7.
12CO (1-0) observations of two Southern dark clouds (globules) associated with cometary nebulae GRV 8 (a biconical nebula) and GRV 16 (a conelike nebula) are presented. GRV 8 shows an outflow from the central part of the nebula (where in 2MASS images a star is located, which is perhaps responsible for this outflow); however, both lobes of the outflow are redshifted with a velocity of +1.95 km/s with respect to the molecular cloud. The two opposite redshifted lobes are a rather rare phenomenon that could be explained by the presence of a double star instead of a single one as the engine responsible for the outflow. The two lobes are almost parallel to the axis of symmetry of the biconical nebula. In the case of the conelike nebula GRV 16 we observe a bipolar outflow, where the eastern blueshifted lobe has a velocity of –4 km/s with respect to the molecular cloud, and the western redshifted one has a velocity +2.5 km/s. The outflow has a direction almost coinciding with the axis of symmetry of the conelike nebula. The star associated with the conelike nebula is responsible for this outflow.Published in Astrofizika, Vol. 48, No. 1, pp. 101–112 (February 2005).  相似文献   

8.
Using the results of observations of the Carina nebula made with the space telescope Glazar, it is shown that the extinction law for the nebula is abnormal and that there is a single OB star complex within the nebula at a distance of about 2200 pc. It is suggested that the observed distribution of OB stars in the nebula and also the appearance of the nebula itself is due to a specific structure of the absorbing clouds within the nebula, and that the absorbing clouds may have such structure as a result of an explosion in the center of the nebula.  相似文献   

9.
Dependencies of galactic planetary nebula chemical abundances and their central star masses on the distance from the galactic plane are discussed.Z-dependencies of He/H, N/H, N/O and Ar/H and dependencies of He/H, N/H, N/O, Ne/H and Ar/H on central star mass are found. Three galactic planetary nebula distance scale samples are used and it is shown that the distance scale system (where distances of each planetary nebula mass class are determined with the separate scale) is the most reliable. The correlations obtained for the Magellanic Cloud planetary nebulae are used for comparison.  相似文献   

10.
A narrow-band Hα image and high-resolution spectroscopy have been obtained in order to investigate the nature of S 266 and its central star MWC 137. The analysis of the stellar and nebular spectra suggests that MWC 137 is a B[e] supergiant located ≥ 6 kpc away from the Sun and not a Herbig Ae/Be star, as it has been traditionally classified. Moreover, the morphology and other properties of the nebula suggest that S 266 is a ring nebula, probably produced by the interaction of stellar winds with the ambient interstellar medium or unprocessed ejected matter. This result would imply that S 266 is the first ring nebula around a B[e] supergiant known in the Galaxy.  相似文献   

11.
Alan Paul Boss 《Icarus》1982,51(3):623-632
Theories of solar system formation often presuppose the existence of the protosun and an accompanying preplanetary nebula. Numerical three-dimensional calculations are presented which demonstrate the possibility of formation of a co-orbital, triple protostellar system, which is unstable to decay to a binary and an ejected single star. The calculations are used to construct a plausible scenario for presolar nebula formation based on a hierarchy of collapse and fragmentation. While this sequence is unlikely to produce many single stars, it remains a possible sequence for the formation of the presolar nebula.  相似文献   

12.
The very young star cluster IC 5146 is studied using star counts, with a view to determining the distribution of interstellar matter in a region where star formation recently occurred. IC 5146 is embedded in a dark nebula which is very dense near its centre. The total mass of interstellar dust in the nebula is found to be about 4.5M ⊙. Comparison of radio and optical observations of the region indicates that gas and dust are not separated to any great degree by radiation from the embedded stars. A gas/dust ratio of about 150/1 by mass is found. This ratio varies with the dust grain model used.  相似文献   

13.
We present narrow band AAO/UKST Hα images and medium and low resolution optical spectra of a nebula shell putatively associated with the Wolf-Rayet star WR 60. We also present the first identification of this shell in the radio regime at 843 MHz and at 4850 MHz from the Sydney University Molonglo Sky Survey (SUMSS), and from the Parkes-MIT-NRAO (PMN) survey respectively. This radio emission closely follows the optical emission. The optical spectra from the shell exhibits the typical shock excitation signatures sometimes seen in Wolf-Rayet stellar ejecta but also common to supernova remnants. A key finding however, is that the WR 60 star, is not, in fact, anywhere near the geometrical centre of the putative arcuate nebula ejecta as had been previously stated. This was due to an erroneous positional identification for the star in the literature which we now correct. This new identification calls into serious question any association of the nebula with WR 60 as such nebula are usually quite well centred on the WR stars themselves. We now propose that this fact combined with our new optical spectra, deeper Hα imaging and newly identified radio structures actually imply that the WR 60 nebula should be reclassified as an unassociated new supernova remnant which we designate G310.5+0.8.  相似文献   

14.
Preliminary results from a search for emission stars in the neighborhood of Cyg OB7 are reported. A new region of size 14×14 arc min lies 12 arc min to the south of HH 448. 17 new objects have been found, of which one is related to a nebula with an interesting shape and, apparently, the characteristics of a cometary nebula. Inside the nebula there are 4 faint, compact formations with very high proper motions. The spectrum of a star shows that it is of spectral class K9-M0 and is a T Tau type star at a distance of 220 pc. Most of the discovered stars with a strong or intermediate Ha emission line intensity are presumably also T Tau stars. This region appears to be a continuation of the T association around HH 448.  相似文献   

15.
We present radio observations of the unique, recently formed, planetary nebula (PN) associated with a very long-period OH/IR variable star V1018 Sco that is unequivocally still in its asymptotic giant branch phase. Two regions within the optical nebula are clearly detected in non-thermal radio continuum emission, with radio spectral indices comparable to those seen in colliding-wind Wolf–Rayet binaries. We suggest that these represent shocked interactions between the hot, fast stellar wind and the cold nebular shell that represents the PN's slow wind moving away from the central star. This same interface produces both synchrotron radio continuum and the optical PN emission. The fast wind is neither spherical in geometry nor aligned with any obvious optical or radio axis. We also report the detection of transient H2O maser emission in this nebula.  相似文献   

16.
The interaction of dust grains with each other in a finite-temperature solar nebula are examined, taking into account the important fact that such grains would carry net steady-state charges like those of grains in interstellar clouds. This charge is given by the well-known Spitzer relation. It provides a screening mechanism that operates during accretion and results in bodies of differing compositions depending on the local temperature in the nebula. In a typical nebula, it is found that planetesimals of 0.1–102-cm size form in a time of order 106–107 years. These planetesimals are of iron and stone and mixed composition in the inner solar system, but of mixed composition only in the outer solar system. The predictions of this type of charged-dust accretion can be compared to known data on meteorites and the composition of the planets.  相似文献   

17.
Isotopic analyses of meteorites suggest the possibility that some interaction between supernova ejecta and grains occurred in the solar nebula. In particular, the dynamics of grain motions in the solar nebula can explain the observed mixing of nucleosynthetic components. The effect of a shock wave on the motions of grains are examined. A steady-state, plane shock propagating into a uniform region of gas and dust grains is followed by a zone of gas/grain slip, in which the grains are accelerated by drag forces from the pre-shock to the post-shock gas velocity, i.e. reducing the relative velocity between the gas and grains to zero. On the basis of these calculations, it is estimated that if grains carried the isotopic anomalies investigated by Lee, Papanastassoiu, and Wasserburg (1978), then those grains could be no bigger than 2×10–4 cm in size. A scenario is suggested in which the sluggishness of grains provides a natural way to concentrate and mix the nucleosynthetic components carried by grains in the ejecta and in the solar nebula.Paper presented at the Conference on Protostars and Planets, held at the Planetary Science Institute, University of Arizona, Tucson, Arizona, between January 3 and 7, 1978.  相似文献   

18.
We present results from observations of H110 α recombination-line emission at 4.874 GHz and the related 4.8-GHz continuum emission towards the Carina nebula using the Australia Telescope Compact Array. These data provide information on the velocity, morphology and excitation parameters of the ionized gas associated with the two bright H  ii regions within the nebula, Car I and Car II. They are consistent with both Car I and Car II being expanding ionization fronts arising from the massive star clusters Trumpler 14 and Trumpler 16, respectively. The overall continuum emission distribution at 4.8 GHz is similar to that at lower frequencies. For Car I, two compact sources are revealed that are likely to be young H  ii regions associated with triggered star formation. These results provide the first evidence of ongoing star formation in the northern region of the nebula. A close association between Car I and the molecular gas is consistent with a scenario in which Car I is currently carving out a cavity within the northern molecular cloud. The complicated kinematics associated with Car II point to expansion from at least two different centres. All that is left of the molecular cloud in this region are clumps of dense gas and dust which are likely to be responsible for shaping the striking morphology of the Car II components.  相似文献   

19.
HD 147010, which is in the reflection nebula vd B 102, has been found to be a hot Ap silicon star rather than a normal A supergiant. From theUBV and JHK photometry of the star, colour excessE(B - V) of 0.29 and the ratio of total-to-selective absorptionR of 4.3 have been obtained. The high value ofR implies bigger grain size and also confirms the association of the star with the nebula. The dereddened colours of the star can be fitted to a theoretical energy distribution with Teff = 13000 ± 500 K and logg = 3.6 ± 0.2. HD 147010 has also been found to be a spectrum variable; in particular, lines of Cr II show large intensity variations.  相似文献   

20.
Spatially resolved, broad Hα line profiles from both the luminous blue variable star ε Carinae (ε Car) and the surrounding filamentary Car II ('Keyhole') nebula, where they have been scattered and reflected by dust, have been observed periodically from 1985 to 1997. The Hα line profiles from ε Car in this 12-yr period show some, albeit not dramatic, changes. The sharp and deep P Cygni-type absorption feature that was observed first in 1985 in the broad, scattered/reflected profiles from the surrounding Keyhole nebula is not present in any of the direct ε Car profiles. This distinctive feature is now shown to be spatially variable over the Keyhole nebula and most prominent along the direction of the axis of the bipolar Homunculus nebula at PA 132°. No evidence of any temporal variability of this sharp feature has been found in 12 yr of monitoring, even from the most well-defined scattering/reflecting cloud along PA 132°.
It is concluded that a 46°-wide cone of light from ε Car is relatively unobscured along the axis of the Homunculus nebula and that this must be the consequence of a dense torus close to the star.  相似文献   

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