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1.
Using the Andersen (1991) data on the mass, absolute visual magnitude, the effective surface temperature and the bolometric corrections, new calibrations for the mass vs. absolute visual magnitude and for the bolometric correction vs. effective surface temperature have been derived. Comparison between the latest evolutionary models with the empirical data has been made to test the evolutionary models for the purpose of stellar population studies.  相似文献   

2.
The Anuradha cosmic ray experiment in Spacelab-3, flown in the orbit at 350 km with an inclination of 57° for about six days, was used to measure the low energy galactic cosmic ray (GCR) heavy ions using a specially designed CR-39 detector module incorporating the arrival time information of the particles. The abundances of sub-iron (Sc-Cr) and iron particles in the low energy interval of 30–300 MeV/N were determined from the measurements made in four different depths of the CR-39 detector module of 150 layers. From these studies we obtained sub-iron (Sc-Cr) to iron abundance ratios of 0.8 to 1.2 in 30–300 MeV/N energy range. It is found that these ratios are enhanced by a factor of two as compared to interplanetary ratios of about 0.5. It is shown that the enhancement of the ratio inside the earth’s magnetosphere is probably due to the degree of ionization of low energy Sc to Cr and Fe ions in the galactic cosmic rays and to the rigidity filtering effects of the geomagnetic field. Further studies are needed to understand fully the phenomena and their implications.  相似文献   

3.
Light curves of the long period RS CVn type eclipsing binary RZ Eri, obtained during the period 1976–1979 with the 1.2 m telescope of the Japal-Rangapur Observatory are analysed, using Wilson-Devinney method, by fixing the two parametersT h (7400°K) andq(0.963), resulting in the following absolute elements:A = 72.5 ± 1.4R ⊙,R h = 2.84 ± 0.12R ⊙,R c = 6.94 ± 0.20R ⊙,M bol,h = 1.35 ± 0.28,M bol ,c= 1.41 ± 0.28,m h = 1.69 ± 0.6m ⊙ andmc= 1.63 ± 0.13m ⊙. The presence of humps and dips of varying amplitudes at a few phases in the normal UBV light curves is explained as due to residual distortion wave. The derived (B-V) and (U-B) colours of both the components appear to have been reddened to an extent of 0 m .20 in (B-V) and 0 m .16 in (U-B) colours. This reddening is attributed to the presence of an envelope around the system, the material of which might have come from the loss of mass experienced by the evolving cooler component. Taking into consideration the dereddened colours and temperatures of the components, spectral types ofF0 IV for the primary and G 5–8 III–IV for the secondary component were derived. The fractional radii of 0.039 and 0.096 of the two components, when compared with the radii of their critical Roche lobes of 0.378 and 0.372 suggest that these components are well within their critical sizes. From the position of the components on the. isochrones and the evolutionary tracks of stars of Pop I composition computed by Maeder & Meynet, it is concluded that the evolution of the components of RZ Eri is abnormal. This system is found to be situated at a distance of 185 pc, with an age of about 2.5 × 109 yrs.  相似文献   

4.
About 460 OB associations were selected by a comparison of theUBV plates. TheUBV photographic photometry of 1944 blue stars in the associations was made. The new associations appear like cores within Humphreys and Sandage's associations. Their star content, size distribution, and mean size 80 pc confirm their identity with the OB associations in the Galaxy and in the Magellanic clouds. The boundaries of the associations are delineated mainly by the density of the resolved stars on theU plates. It is impossible to divide them into smaller areas. The genuine OB associations form groups of two or more members with a length scale of 250 pc. Their boundaries were delineated independently, but they coincide with the OB associations of Humphreys and Sandage (1980). These groups represent real concentration of blue massive stars with a large age dispersion. The star complexes unify a group of associations,Hii regions, andHi peak distribution. Their mean size is 570 pc. The extensiveHi clouds with a mean size of 1.2 kpc contain two or more star complexes. The questions related to star formation are briefly discussed.  相似文献   

5.
In this study we investigated the effects of external trigger on the characteristics of young stellar objects (YSOs) associated with cometary globules (CGs). We made optical spectroscopy of stars associated with star-forming CGs. We find that the masses of the most massive stars associated with CGs are correlated with the masses of the parent cloud but they are systematically larger than expected for clouds of similar mass from the relation M max-star=0.33M cl 0.43 given by Larson (Mon. Not. R. Astron. Soc. 200:159, 1982). We have also estimated the luminosities of the IRAS sources found associated with CGs as a function of cloud mass and then compared them with those of the IRAS sources found associated with isolated opacity class 6 clouds (isolated and relatively away from large star forming regions). We find that the luminosities of IRAS sources associated with CGs are larger than those of the opacity class 6 clouds. These findings support results from recent simulations in which it was shown that the Radiation Driven Implosion (RDI) process, believed to be responsible for the cometary morphology and star formation, can increase the luminosity 1–2 orders of magnitudes higher than those of protostars formed without external triggering due to an increase in accretion rates. Thus implying that the massive stars can have profound influence on the star formation in clouds located in their vicinity.  相似文献   

6.
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   

7.
In this paper we estimate the star formation efficiency using the assumption that star formation continues until the radiation pressure disrupts the cloud. The results that in the case of low/mediummass star formation the efficiency could be about five times higher than in the case of high-mass star formation.For a three-component star-forming system (low/medium-mass stars, high-mass stars, gas) we investigate the temporal behaviour and the final star formation efficiency. We can show that the efficiency in 104 M clouds is higher than in 106 M clouds. This supports our view that bound stellar systems form from medium-mass clouds, whereas OB associations form in the cores of giant molecular clouds. Furthermore, the effect of induced high-mass star formation may cause a change of the mass spectrum during the formation of an OB association.Paper presented at a Workshop on The Role of Dust in Dense Regions of Interstellar Matter, held at Georgenthal, G.D.R., in March 1986.  相似文献   

8.
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   

9.
The relation between molecular clouds, star clusters, and the stellar component of the galactic disk is investigated. According to Elmegreen (1985) bound stellar systems, e.g., open star clusters, can be formed from molecular cloud of mass 104 M . A close encounter with a giant molecular cloud or massive black hole disrupts such stellar systems and forms superclusters. This explains why some open star clusters are so mass-deficient. Unbound stellar systems, e.g., expanding OB associations, are formed from molecular clouds of mass 105 M . When disruptive O-type stars appear the star formation is halted and the cloud is destroyed. An example of the relict of GMC disruption in the solar vicinity is Gould's belt. The velocity dispersion-versus-age relation is also investigated and explained as a consequence of gravitational scattering of stars on GMC, or massive black holes, or as due to recurrent transient spirals.Paper presented at a Workshop on The Role of Dust in Dense Regions of Interstellar Matter, held at Georgenthal, G.D.R., in March 1986.  相似文献   

10.
Consideration is given to a search for relativistic objects in massive close binary systems without strong X-ray emission (L x <1034 erg s–1). It is pointed out that, according to the present-day theory on the evolution of massive close binaries, the number of neutron stars and black holes in non-X-ray binary systems must be 100 times the number of the known X-ray binaries comprising OB supergiant stars; that is why, in studying non-X-ray binary systems, the chances are to detect about a hundred of black holes in the Galaxy.Criteria are formulated for the relativistic nature of companions in the binary systems, such as high spatial velocity values and height Z over the galactic plane for OB stars (runaway stars) and for Wolf-Rayet stars. As reported by Tutukov and Yungelson (1973), as well as by van den Heuvel (1976), the presence of ring-type nebulae can serve as another indication of a relativistic nature of companions in the case of Wolf-Rayet stars.Data are collected on Wolf-Rayet stars with low-mass companions (Table I), which can be relativistic objects accreting within a strong stellar wind from Wolf-Rayet stars. Presented are new findings in respect of spectral examination of the runaway OB-stars (Table II), bringing together data on eight OB stars which can represent binary systems with relativistic companions (Table III).A list of 28 OB-stars (Table IV) which offer a good chance for finding relativistic companions is given.  相似文献   

11.
Based on the Hipparcos catalog and the radial velocities of stars published to date, we perform a kinematic analysis of OB stars. Parameters of the general Galactic rotation were determined from distant OB stars. We used the residual velocities of stars corrected for the general Galactic rotation to study the proper rotation of nearby OB stars. Geometrical characteristics of the Gould Belt were estimated by analyzing its kinematic parameters. We obtained parameters of peculiar solar motion as well as parameters of the proper rotation, expansion, and contraction for rotation around both the Galactic z axis and an axis perpendicular to the plane of symmetry of the disk. Kinematic parameters of the proper differential rotation were found for two age groups of nearby OB stars. Almost all of the nearby OB stars were shown to rotate in the same direction as the Galactic rotation. We constructed rotation curves.  相似文献   

12.
The symmetric trace free (STF) tensor formalism, developed by Hartmann et al. (Celest Mech Dyn Astron 60:139–159. doi:10.1007/BF00693097, 1994), is a nice tool, not much used in Celestial Mechanics. It is fully equivalent to the usual spherical harmonics but permits more elegant and compact formulations. The coupling between the gravitational fields of extended bodies with this formalism has been used in Mathis and Le Poncin-Lafitte (Astron Astrophys 497:889–910. doi:10.1051/0004-6361/20079054, 2009) for binary stars or planetary systems, but not yet applied to binary asteroids. However, binary asteroids are common in the Solar System and usually their study requires a full two rigid body approach. The formulation of the two-body interaction potential in the STF formalism in the full two rigid body problem is detailed and completed in this article. An application to the binary asteroid (66391) 1999 KW4 is presented with a comparison of our results with other results of the literature for validation.  相似文献   

13.
A new method of determination of distances to stellar associations is proposed. This method is based on the measurements of mean thicknesses of globules of the systems of dark globules connected with that association. It is shown that the method is in good agreement with other known methods. A new grouping of OB stars in Pup-CMa is found. It is shown that this grouping has properties characteristic for OB-associations: the stars of that grouping have similar distances, similar radial velocities, the grouping is connected with molecular clouds, with Herbig-Haro objects, and cometary nebulae. All these results are in favour of this grouping to be a new OB-association. We named that association OB-association Pup-CMa. The preliminary results of12CO observations of molecular clouds connected with that association are also given. The radial velocities of these clouds are in good agreement with the mean radial velocity of stars in the association in Pup-CMa. Translated from Astrofizika, Vol. 42, No. 2, pp. 179–188, April–June, 1999.  相似文献   

14.
The OB stars are concentrated near the Galactic plane and should permit a determination of the distance to the Galactic center. van Leeuwen’s new reduction of the Hipparcos catalog provides, after 824 Gould belt stars have been excluded, 6288 OB stars out to 1 kpc and Westin’s compilation an additional 112 stars between 1 kpc and 3 kpc. The reduction model involves 14 unknowns: the Oort A and B constants, the distance to the Galactic center R 0, 2 second-order partial derivatives, the 3 components of solar motion, a K term, a first order partial derivative for motion perpendicular to the Galactic plane, a second-order partial for acceleration perpendicular to the plane, two terms for a possible expansion of the OB stars, and a C constant. The model is nonlinear, and the unknowns are calculated by use the simplex algorithm for nonlinear adjustment applied to 14313 equations of condition, 12694 in proper motion and 1619 in radial velocity. Various solutions were tried: an L1 solution, a least squares solution with modest (2.7 %) trim of the data, and two robust least squares solutions (biweight and Welsch weighting) with more extreme trimming. The Welsch solution seems to give the best results and calculates a distance to the Galactic center 6.72±0.39 kpc. Statistical tests show that the data are homogeneous, that the reduction model seems adequate and conforms with the assumptions used in its derivation, and that the post-fit residuals are random. Inclusion of more terms, such as streaming motion induced by Galactic density waves, degrades the solution.  相似文献   

15.
The stellar field centred close to theh and Per double cluster is one of the 123 fields recorded in the galactic plane at 2000 Å by the balloon-borne stratospheric gondola of the SCAP-2000 programme. The analysis of the frame allows us to determine an ultraviolet colour indexU 1-V for more than 600 stars. Among these are stars belonging to theh and Per and Tr 2 clusters and to the PER OB1 association. The prevailing extinction law is found to produce greater extinction at 1965 Å than predicted by the mean extinction law. Moreover, the clouds responsible for the extinction are situated in the local arm and distributed in two layers with a very transparent interval. The comparison of theA v extinction and theHI and CO abundances leads us to assume the presence of a H2 cloud in front ofh and Per, in the second absorbing layer and, therefore, in the local arm. The two absorbing layers and the molecular cloud are perhaps in the plane of the Gould belt and associated with the expanding gas detected by Lindblad. A group of hot stars centred at the same distance as this molecular cloud has been detected and could form an association of OB stars in the local arm. Other, much more distant OB stars belonging to the Perseus arm of Efremov's list. Several stars which must have a very hot companion are detected in the field.  相似文献   

16.
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17.
Star formation     
Various topics on star formation, centered on the observed properties of young stars and their environment, are reviewed. (a) In our Galaxy, young stellar objects are generally associated with giant molecular clouds. (b) Giant molecular clouds cannot be in free-fall collapse. They are probably stabilized by magnetic fields, which are then likely to dominate the dynamical evolution of the clouds themselves. (c) Star formation occurs mostly in spiral arms. The role of spiral density waves is however not yet clearly understood. (d) The formation of massive stars can perturb the evolution of the progenitor cloud, and possibly trigger the sequential formation of OB subgroups. (e) There is a large number of clouds in the Galaxy associated only with low and intermediate mass young stars. These clouds are not perturbed by the presence of massive stars, and are probably the best source of information on the primary triggering mechanism, active on a galactic scale, and on the initial conditions for star formation.Paper presented at the European Workshop on Planetary Sciences, organised by the Laboratorio di Astrofisica Spaziale di Frascati, and held between April 23–27, 1979, at the Accademia Nazionale del Lincei in Rome, Italy.  相似文献   

18.
From the standpoint of view that the early type stars are formed sequentially at an OB association, it is expected that the supernova explosions will also occur sequentially. We study the expansion law of a supernova remnant, which is formed by sequential explosions of supernovae. The superbubbles and supershells with the radii 2001000 pc are naturally explained by this model. Assuming that the sequential explosion of supernovae occurs at every OB association, we deduce the star formation rate in our Galaxy.  相似文献   

19.
The spatial distribution of O-type stars projected onto the Per OB1 association has been investigated. From the limited data available we find evidence to suggest that there are several distinct clusters of early type stars in the association's line of sight. It is found that all those stars identified in the past as being blue stragglers are likely situated in the most distant cluster and consequently they are unlikely to be coevally related to the closer stellar groups. Our argument is that all those stars previously classified as blue stragglers in Per OB1 are normal O and OBN stars.  相似文献   

20.
Photodesorption from dust grains by an anisotropic radiation field will lead to much greater momentum transfer than that associated with radiation pressure. This can cause the segregation of dust to the centres of moderately dense interstellar clouds.  相似文献   

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