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1.
This paper presents the results of monochromatic [Oiii], [Nii], and [Sii] observations of ring nebula Sh157 around the star (WR + B0III) HD 219460 belonging to the Ba 3 cluster. A stratification of radiation typical for photoionization excitation has been revealed. The observations suggest that the Sh157 ring structure may arise as a result of the HD 219460 stellar wind blowing the surroundingHii region, and the bubble age is found to bet(2–5)×105 yr. Three outer envelopes have been distinguished: a weaker extended emission shell apparently blown out by the wind from B-stars of the Ba 3 cluster, and two dust shells which are likely to be associated with NGC 7510 and Cas OB2. The paper is also concerned with the discussion of young star aggregates Ba 3, NGC 7510, Cas OB1, OB2, OB4, OB5, OB7, and Cep OBI and the associatedHii regions, shells and supershells of gas and dust, molecular clouds, and supernova remnants which may be probable members of a single giant stellar complex where the star formation process is in progress.  相似文献   

2.
通过角动量守恒计算,证明了原始星云角动量不足,单纯靠星云自转惯性离心力无法抗衡中心部位星云的吸引力,无法在星云赤道处形成星云盘.原始星云角动量不足,同时星云收缩时径向方向速度不等,内快外慢,结果中心部位星云形成太阳,外部赤道部位星云物质因赶不上内部星云物质收缩而掉队形成星云盘.再由星云盘分裂、掉队形成星云环;星云环形成行星、卫星.对太阳系一些主要特征,作了分析和说明.  相似文献   

3.
Based on a LogN-LogS relation we have shown that the EGRET unidentified source (UnidS) distribution closely follows the Galactic spiral arm structure. This seems to satisfy the hypothesis that the EGRET UnidS arise due to energetic interactions with molecular clouds that reside on the spiral arms. Furthermore, the luminosity distribution of the unidentified sources features a double Gaussian distribution. We suggest that a combined distribution of OB associations, SNR and superbubbles interacting with molecular clouds within the spiral arms are the most likely counterparts of the unidentified sources.  相似文献   

4.
The distribution of 255 O-B9-A2, K-G stars and interstellar dust in the direction of the stellar cluster NGC 1893 is studied using V, B-V, and U-B photometric data. Sixteen groups of stars (associations) are discovered at various distances. The first group includes 9 stars of different spectral classes of later types in the sun’s neighborhood lying at a distance of 110 pc. The next 3 groups, at distances of 420, 890, and 14300 pc, are type B associations and the remaining twelve groups are OB associations. They are designated as Aur 0.11, Aur B 0.43, Aur B 0.89, Aur OB 1.4, Aur OB 2.6, AurOB 3.8, Aur OB 4.6, Aur OB 5.4, Aur OB 6.1, Aur OB 7.4, Aur OB 9.3, Aur OB11.6, Aur OB14.3, Aur OB 17.9, Aur OB 25.9, and Aur OB 31.3. For most of these stars the absorption lies within the range from 0m.45 to 5m.41. Such high absorption may be caused by circumstellar absorption as well as by the diffuse nebula IC 410. The dusty matter is distributed nonuniformly in the Aur 0.11, Aur B 0.43, and Aur B 0.89 associations. There is no dust in the space between the associations. There is essentially no dust within the groups (associations) at distances greater than 0.9 kpc. (See Table 2.) __________ Translated from Astrofizika, Vol. 50, No. 2, pp. 243–251 (May 2007).  相似文献   

5.
Some of the peculiar features of the periodic velocity-field structure for OB associations can be explained using the Roberts-Hausman model, in which the behavior of a system of dense clouds is considered in a perturbed potential. The absence of statistically significant variations in the azimuthal velocity across the Carina arm probably results from its sharp increase behind the shock front, which is easily blurred by distance errors. The existence of a shock wave in the spiral arms and, at the same time, the virtually free motion of OB associations in epicycles can be reconciled in the model of particle clouds with a mean free path of 0.2–2 kpc. The velocity field of OB associations exhibits two appreciable nonrandom deviations from an ideal spiral pattern: a 0.5-kpc displacement of the Cygnus-and Carina-arm fragments from one another and a weakening of the Perseus arm in quadrant III. However, the identified fragments of the Carina, Cygnus, and Perseus arms do not belong to any of the known types of spurs.  相似文献   

6.
The present-day observed mass distribution in the solar system including the Sun is shown to be compatible with the idea of the splitting of a number of ring-shaped rotating clouds of particles in the equatorial plane of a single contracting nebula. The formation of such a nebula is discussed and it is inferred that during the course of contraction this nebula has remained a sphere of uniform density spinning with the Keplerian velocity of its surface layer. The mass of a planet is taken as the portion of this spherical solar nebula gained at the time of splitting by its gaseous ring of dimensions satisfying Roche and accretional limits.  相似文献   

7.
On the basis of observations by the space telescope Glazar at 1640 Å the distribution of early (O-B-A) type stars and absorption matter in the directions of 20 known OB associations have been investigated. Forty-four stellar groups were found in these directions. The dust matter is distributed within these groups quite non-uniformly and patchy. It is absent in the space between these groups. It has been shown that 93 stars have dense circumstellar dust envelopes and half of them are sources of IR-radiation (IRAS observations). Dust clouds exist in the directions of Per OB1, Aur OB1 and Car OB1 at distances of 460, 1000, 1000 pc, respectively. Twenty new stellar groups of OB types were found.Published in Astrofizika, Vol. 38, No. 4, pp. 528–532, October–December, 1995.  相似文献   

8.
Supersonic non-central collision and coalescence of interstellar matter clouds is suggested as a physical process that could lead to the formation of a solar nebula with an appropriate distribution of the spinangular momentum.  相似文献   

9.
The results of observations of 159 stars at 1640 Å in Puppis made with the space telescope Glazar are presented. It is shown that the observed stars are members of different groups of stars situated at distances of about 120, 370, 700, 1250, 2400, and 4000 pc. The last two groups belong to the Pup OB1 and the Pup OB2 stellar associations.There is relatively little absorption in the observed region. The absorbing matter is mainly concentrated in small clouds.It is suggested that three stars — CP –27°4197, HD 60479, and HD 61672-are embedded in a dust envelope and that the star HD 60057 has a hot subdwarf companion.Forty-four of the observed stars are new OB or early A-type stars, spectral types of which were not known.  相似文献   

10.
We investigate the formation of star clusters in an unbound giant molecular cloud, where the supporting kinetic energy is twice as large as the cloud's self-gravity. This cloud manages to form a series of star clusters and disperse, all within roughly two crossing times (10 Myr), supporting recent claims that star formation is a rapid process. Simple assumptions about the nature of the star formation occurring in the clusters allows us to place an estimate for the star formation efficiency at about 5–10 per cent, consistent with observations. We also propose that unbound clouds can act as a mechanism for forming OB associations. The clusters that form in the cloud behave as OB subgroups. These clusters are naturally expanding from one another due to the unbound nature of the flows that create them. The properties of the cloud we present here are consistent with those of classic OB associations.  相似文献   

11.
Spectral and morphological studies of an infrared nebula in the neighborhood of Cyg OB7 discovered in 2007 are reported. It is shown that over the last several years the brightness and shape of the nebula have changed significantly. Spectral observations of the nebula made with the 2.6-m telescope at the Byurakan Observatory in 2004 and 2005 reveal the existence of a faint trace of continuum spectrum, indicating the existence of a star inside the dark cloud. Classification of these spectra shows that over one year the star’s spectral class changed from late G to early K. It is also shown that the absorption in the direction of the nebula is as high as 8m–10m. __________ Translated from Astrofizika, Vol. 50, No. 1, pp. 17–27 (February 2007).  相似文献   

12.
The presolar nebula may have formed from the collapse of a very slowly rotating interstellar cloud. The first three-dimensional, hydrodynamical calculations of the collapse of such clouds are presented. The models include radiative transfer in the Eddington approximation, as well as detailed equations of state appropriate for the nonisothermal regime of protostellar evolution. Very slowly rotating clouds, i.e., those with initial ratios of rotational energy to gravitational energy of 10?3 or less, avoid fragmentation and instead collapse to form single central objects, containing quasistatic cores with densities of about 10?10 g cm?3. These cores are, however, surrounded by significantly nonaxisymmetric regions, such that the presolar nebula would have been bar-like over the scale of the present solar system. This nonaxisymmetry, coupled with differential rotation, results in gravitational torques that produce rapid outward transfer of angular momentum. The center of the presolar nebula should then be able to contract and collapse to pre-main-sequence densities without suffering fission or fragmentation.  相似文献   

13.
We compare the line-of-sight velocities of stars in OB associations within 3 kpc of the Sun and the molecular clouds closest to them. The Perseus arm is used as an example to show that the line-of-sight velocity ranges in which OB-association stars, molecular clouds, and H II regions ionized by these association stars are observed overlap. The streaming motions produced by density waves in the (l, VLSR) plane were found to lead to an inversion of the distances to objects of the Perseus arm and the interarm space beyond this arm.  相似文献   

14.
To investigate the kinematics of the neutral material around the Gum nebula, emission from hydroxyl at 1667 MHz was observed at many positions over the region. Fitting models of expanding shells to these data together with previously published molecular line data shows that the diffuse molecular clouds and cometary globules form a single expanding shell centred on G261−2.5. The mean angular radius is 10.5° and its maximum radius is 14°. The models show that the distance range to the expansion centre is from 200 pc to 500 pc.
The path of the runaway O-star ζ Puppis passed within <0.5° of the expansion centre of the neutral shell ∼1.5 Myr ago. The supernova of the erstwhile binary companion of ζ Puppis is the probable origin of the Gum nebula and the swept up expanding neutral shell. The 500-pc distance to the supernova is adopted as the distance to the expansion centre of the neutral shell. At this distance the energy required to produce the observed expansion could have been met with a single supernova. The radii of the front and back faces of the shell are 130 and 70 pc respectively. The front face is expanding faster than the back face, at 14 and 8.5 km s−1 respectively.
The extent of the neutral shell matches the radio continuum and H α emission of the Gum nebula well. The photoionized gas in the nebula is probably primarily ionized by ζ Puppis, which is still within the neutral shell. No evidence was found for the IRAS -Vela shell as a separate expanding shell.  相似文献   

15.
Based on our Hα interferometric observations and CO data, we analyze the structure and kinematics of the gas in an extended region of the Cygnus arm around the recently discovered star WR 142a. We have established that WR 142a and the ionized hydrogen in its immediate neighborhood are associated with the complex of molecular clouds observed in a region with l ～ 78°–80°30′, b ～ 2°–3°20′, and V LSR ～ 4–16 km s?1. Traces of the action of the stellar wind from WR 142a on the ambient gas have been found to the northeast of the star in a region devoid of dense absorbing foreground clouds. These include very weak thin gas and dust filaments as well as high-velocity components of the Hα profile, which can be interpreted as a possible expansion of the shell swept up by the wind with a velocity as high as 50–80 km s?1. Giant regions of reduced CO emission dominated by high-velocity motions of ionized hydrogen have been detected. Stars of the Cyg OB2 association and the cluster NGC 6910 can be responsible for these motions.  相似文献   

16.
The dependence of interstellar extinction on distance in the direction of a dark cloud around the reflection nebula NGC 1333 is determined on the basis of photoelectric Vilnius photometry and photometric classification of 78 stars. Two dust clouds are noted at distances 160 and 220 pc. The first one with mean extinction of 0.4 mag is concluded to belong to the Taurus cloud complex and the second cloud with mean extinction of 1.8 mag belongs to the chain of dark clouds and other young objects which is almost perpendicular to the spiral arm but lies 80 pc below the galactic plane. The star BD +30°549 which illuminates the NGC 1333 nebula is at distance 212 pc from the Sun. No extinction increase behind the Perseus cloud is detected.  相似文献   

17.
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   

18.
Several previous studies in and around the Great Carina nebula (NGC 3372) have strongly indicated an abnormal interstellar extinction law with a high ratio of total to selective absorptionR. In the present study, newUBV photometric data and accurate MK spectral-types of stars in the region of the Carina OB2 association are used to show that (1) Car OB2 is a genuine stellar association located at a distance of 3.2 kpc, and (2) the interstellar extinction law seems to be normal throughout most of the region. A representative value ofR = A v/E(B – V) = 3.0 is derived for Car OB2 from the variable extinction method.Visiting Astronomer, Cerro Tololo Inter-American Observatory, operated by AURA, Inc. under contract with the National Science Foundation.  相似文献   

19.
Massive stars have significant influence on the evolution of the interstellar medium. Bright rims, cometary morphology of clouds, as well as their motion are some examples of the influence of massive stars on nearby molecular clouds. The cometary clouds in the Gum-Vela region are very good examples. In an attempt to understand the kinematics of the clouds in such regions we have carried out CO line observations towards bright-rimmed clouds near the OB Association Cep OB2. The radial velocities of the clouds are consistent with an expansion of the system at ≈ 4kms?1 away from the dominant O6.5V star in the association, HD206267. We find the rocket mechanism to be the most likely cause for expansion as found for both the Gum-Vela and the Rosette globules. We conclude that such expanding motions are quite common in regions near massive stars and make a brief comparison of the Cepheus system with the Gum-Vela system.  相似文献   

20.
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   

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