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1.
We describe initial results of a program to image massive newly-formed stars with sub-arc second spatial resolution. We discuss high-precision diffraction-limited size measurements at =10 m made using the 3 m Lick telescope. The point-spread function has FWHM 0.7; deconvolution yields a spatial resolution of 0.35. We find that the core component of one such object, LkH 101, is unresolved at these scales, and we are able to set a 95%-confidence upper limit of 270 AU for the diameter of the circumstellar dust shell. This places the dust at the same radial scale as a strong ionized stellar wind region seen at radio wavelengths. Our observations, when combined with published spectral observations, rule out an optically thick circumstellar disk but allow a radially thin, anisotropic distribution of dust, or alternatively an isotropic distribution of dust with a narrow range of large grain sizes.  相似文献   

2.
Some planetary nebulae in the galactic thick disk display extremely low abundances of heavy elements such as O, Ne, S, and Ar, compared with normal or type II nebulae. Their central stars are generally relatively cool and underluminous, indicating that the progenitor stars had very low masses. It is suggested that strong stellar winds have had an important role in the formation of these objects, which is supported by the large mass loss rates now observed.  相似文献   

3.
A number of criteria are elaborated based on the careful analysis of nebulae images which confirm the version of the origin of double-envelope planetary nebulae by means of dynamical separation but not by multiple ejection. The importance of stellar winds in the origin of the gigantic halos around double envelope nebulae is outlined. The problem concerning the existence of two types of filamentary planetary nebulae (Figure 8) is raised: type A, filaments are the fragmentations of the Rayleigh-Taylor instability, the result of dynamical interaction of the envelope with the outer interstellar matter (NGC 6543), and type B, the origin of filaments is connected with the Magnetic field fluctuations (A 43, A 72).The possibility of the origin of three-envelope nebulae in the framework of the dynamic separation version is discussed (NGC 7293). Attention is paid to the impossibility of outbursts with low velocities (20–30 km s–1) from hot stars, i.e., the nuclei of nebulae.  相似文献   

4.
The determination of the luminosities of planetary nebula central stars from H nebular fluxes is investigated. A correlation is obtained with the luminosities derived from independent stellar parameters. An average scaling factor is determined for H luminosities of optically thick nebulae, as well as correlations of this parameter with the Zanstra He II and H I temperatures.  相似文献   

5.
, . () . , , , . ( ), , , . . (2.7). ( 1 k 1 ,V — , — .) (k 1) (k) §2 ( (2.14)). , (3.6) (3.4), (3.8) . (3.9)–(3.13) ( (3.9), (3.10) (3.11) , (3.12)–(3.13) ). (3.14), (3.16)–(3.19). - . (3.15). ( (4.14)–(4.15)). (4.23)–(4.25). (4.26)–(4.28). §5. , . ((5.5)–(5.6)). , . (5.10) .  相似文献   

6.
A model of -bursts is considered that treats the flares of neutron stars as a result of convectiveoscillation instability associated with the stars having strong internal magnetic fields ( 1013 to 1014 G). In the context of this model only sufficiently old (104 to 107 yr), drastically cooled-down neutron stars may be sources of -bursts. The paper shows that major characteristics of a -burster in the Supernova N 49 remnant (energy release during burst up to 1044 erg, age 104 yr, burst-to-burst interval (I to 3)×106s; rotation period P=8 s) may be explained under the assumption that the mass of the neutron star is about 0.14M · while its mean magnetic field strength is 1.5×1014 G abd 1013 G within the star and on its surface, respectively. The observational tests of the model discussed conclude the paper.  相似文献   

7.
Assuming that some exchange of energy between stars in the galactic disk may be at work, I have generalized the formulae expressing the growth of the velocity variance with time by adding a mass term (M/M )– with =0.35, which is a good fit to the kinematic data for young stars. The generalized formulae (5a) and (5b) and the evolutionary mass-age relation (Iben, 1967) were used jointly to derive mass and age values for different stellar species. The results, presented in Table IV, are followed by a discussion.  相似文献   

8.
According to theory, stars more massive than 8 M must form while still accreting material from the surrounding parental cloud: at this stage radiation pressure should reverse the infall thus preventing further growth of the stellar mass. After illustrating the two models proposed to solve this problem (accretion and coalescence), we review the observational evidence pro/contra such models, focusing on the kinematics of the molecular gas where the massive (proto)stars are embedded as the best tool to shed light on the formation mechanism. Special attention is devoted to the phenomena of infall, outflow, and rotation, concluding that the recent detection of rotating disks in massive young stellar objects is the best evidence so far in favour of the accretion model.  相似文献   

9.
It is shown that the observed color diagrams(U-B) f (B-V) f for pure flare emission of UV Cet type flare stars may be explained within the framework of a fast electron hypothesis. We point out the essential influence on these color indices of the two following factors: (a) the deviations of the normal radiation capability of the star in the infrared region of spectra (on 3.6 m, 4.4 m, and 5.5 m) from the Planckian distribution; (b) the location of the cloud (source) of fast electrons around the star (flare geometry effect). Under the real conditions of the generation of flares around the star the frequency transformation law at the photon-electron interaction has a view =n20, wheren may take the different values-from 0.15 up to 4; it depends on the cloud-star-observer geometry. By the observed colors of the flare emission may be understood, in principle, the location of flare source around the star. A possible role of reflection effect at the generation of stellar flares is outlined.  相似文献   

10.
Optical identification of infrared sources from the IRAS Point Source Catalogue (PSC) is made by means of low-dispersion spectra of the First Byurakan Survey (FBS) and Palomar Observatory Sky Survey (POSS) red and blue images. The purpose of this work is to examine the composition of the PSC sample of fainter sources at high galactic latitudes and to reveal QSOs, infrared galaxies, red stars (C and M), planetary nebulae, for their further investigation at the optical range. 100 of 108 unknown IRAS sources in the region with 3h50m 7h40m and + 69° + 73° are optically identified. Optical coordinates, V magnitudes, color indices, and preliminary classes are determined. According to preliminary classification 3 objects turned out to be QSOs, 36 are galaxies with very interesting morphology, 5 are faint planetary nebulae, 9 are carbon stars, and 47 are late M-type stars.Published in Astrofizika, Vol. 38, No. 4, pp. 625–629, October–December, 1995.  相似文献   

11.
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   

12.
The modern self-consistent photoionization model of planetary nebula luminescence is described. All of the processes which play an important role in the ionization and thermal equilibrium of the nebular gas are taken into consideration. The diffuse ionizing radiation is taken into account completely. The construction of the model is carried out for the radial distribution of gas density in the nebular envelope which is consistent with isophotal map of the nebula. The application of the model is illustrated on the example of the planetary nebulae BD+30°3639 and NGC 7293. It is shown that the continuum of the central star at 912 Å does not correspond to the blackbody spectrum but agrees with the spectrum of corresponding non-LTE model atmosphere. The radial distributions of electron density, electron temperature, and other parameters in the nebular envelopes are found.The evolution of the radial distribution of gas density in the planetary nebulae envelopes is investigated. Approximative analytical expression which describe both such distribution and its change with time is adjusted. It is shown that the nebular envelope is formed as a result of quiet evolution of the slow stellar wind of star-precursor, and the formation of the envelope begins from the decrease of star-precursor's mass loss rate. Obtained radial distributions of gas density in the envelopes of young nebulae rule out the idea that the planetary nebula is formed as a result of a rapid ejection of clear-cut envelope. So, there is no necessity for the superwind which is used for this purpose in theoretical calculations.A new method of the determination of planetary nebulae abundances is proposed. Unobserved ionization stages are taken into account with aid of the correlations between relative abundances of various ions which had been obtained from the grid of the photoionization models of planetary nebulae luminescence. Simple approximative expressions for the determination of He/H, C/H, N/H, O/H, Ne/H, Mg/H, Si/H, S/H, and Ar/H are found. The chemical composition of 130 Galactic planetary nebulae is revised. A comparative analysis of the abundances in the Galactic disk, bulge, and halo nebulae is carried out.  相似文献   

13.
C12 stars in the range 1.04–1.55M are evolved to simulate the core evolution of the possible precursors of planetary nebulae. The nuclear shell burning in stars above 1.2M advances to within about 0.2M of the surface, where the intense radiation interacts with the surface matter and causes mass loss. Comparison between our theoretical results and observations suggests that this may be a mechanism by which planetary nebulae are formed.Presented at the Trieste Colloquium on Mass Loss from Stars, September 12–16, 1968.  相似文献   

14.
The solar causes of geomagnetic disturbances   总被引：1，自引：0，他引：1  
Geomagnetic disturbances have been identified with respect to their sources for 1977–1983. The disturbance level was found using the daily planetary index A p. High-amplitude ( 50), mean-amplitude (24) and low-amplitude ( 12) disturbances are caused by solar flares of importance 1, coronal holes, and filament cavities, respectively. The ranges of probable amplitudes of disturbances of different nature and their relative number are found from Poisson random distributions of amplitudes.  相似文献   

15.
The formation of the gas giant planets Jupiter and Saturn probably required the growth of massive 15 Earth-mass cores on a time scale shorter than the 107 time scale for removal of nebular gas. Relatively minor variations in nebular parameters could preclude the growth of full-size gas giants even in systems in which the terrestrial planet region is similar to our own. Systems containing failed Jupiters, resembling Uranus and Neptune in their failure to capture much nebular gas, would be expected to contain more densely populated cometary source regions. They will also eject a smaller number of comets into interstellar space. If systems of this kind were the norm, observation of hyperbolic comets would be unexpected. Monte Carlo calculations of the orbital evolution of region of such systems (the Kuiper belt) indicate that throughout Earth history the cometary impact flux in their terrestrial planet regions would be 1000 times greater than in our Solar System. It may be speculated that this could frustrate the evolution of organisms that observe and seek to understand their planetary system. For this reason our observation of these planets in our Solar System may tell us nothing about the probability of similar gas giants occurring in other planetary systems. This situation can be corrected by observation of an unbiased sample of planetary systems.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.  相似文献   

16.
A non-LTE study of the Type IIb supernova 1993J in the galaxy M81 taking into account nonthermal ionization and line blocking effects is carried out. Hydrodynamical models and theoretical spectra clearly show that nonthermal ionization and excitation dominate after the second maximum, at day 30, and play a decisive role in reproducing both the smooth tail of the light curve and the emergence of helium lines in the spectrum, similar to those observed. Based on our model of supernova 1993J, we predict that the light curves of Type Ib supernovae should be subject to nonthermal ionization and excitation at earlier times than even those for supernova 1993J. In our model, the outburst of supernova 1993J is interpreted as the explosion of a 4 M red supergiant, which underwent core collapse and left a neutron star in a binary system. The progenitor is supposed to have a helium core mass of 3 M, corresponding to a 13 M main-sequence star. Supernova 1993J adds evidence to the scenario that Type Ib supernovae originate from moderately massive stars on the main sequence that have lost their hydrogen envelopes in interacting binary systems.  相似文献   

17.
A 3 mm low noise beam-lead Schottky diode mixer has been developed. At cryogenic temperatures the conversion loss is 6.3 dB, and the DSB mixer noise temperature is 75 K, respectively. The mixer was installed into the cooled receiver for radioastronomical observations at the Metsähovi 13.7-m radio telescope. Total DSB noise temperature of the cooled receiver with an ultra low noise HEMT IF amplifier was 110 K at 103 GHz. The tuning range of the mixer mount was from 70 GHz to 115 GHz.  相似文献   

18.
Stochastic simulations of galaxy fields, using the cluster multiplicity function obtained for the Lick galaxy counts, reproduces satisfactorily the observed distribution of galaxies from COSMOS measures on a deep UKST and AAT plate limited atB22.0 andB23.2, respectively. The results imply that no strong evolutionary effect is present in the clustering of galaxies, at least out to redshiftsz *0.65.  相似文献   

19.
The pulse-period distribution of binary X-ray pulsars has been considered. A gap in this distribution, in the period rangeP10 s toP100s has been explained in terms of the character of mass transfer in the X-ray binary systems. It is shown that this gap arises because the rotating magnetised neutron stars in these systems are slowed down by accretion torques, either toP10 s when the mass transfer is by means of Roche-lobe overflow in low mass binaries, or toP100 s by stellar winds in massive binaries. The gap is maintained as the slow pulsars (P>100 s) in their spin-up phase cross the gap in a time short compared to their life-time, because of the increase in mass transfer with the evolution of the normal star.  相似文献   

20.
We present 9.7 and 11.8 m narrow band (/=10%) images of three carbon (C-) rich proto-planetary nebulae with an unusual 21 m feature: IRAS 07134+ 1005, IRAS 22272+5435, and IRAS 04296+3429. The images were taken at UKIRT using the Berkeley/IGPP/LEA mid-IR camera. All three objects have a bipolar shape adding to the existing evidence that C-rich PPNe are by nature bipolar. Furthermore, we find the same bipolar morphology in a previous study of the C-rich, young planetary nebula, IRAS 21282+5050. We believe these four objects form an evolutionary sequence which links the C-rich asymptotic giant branch (AGB) stars with the C-rich planetary nebulae (PNe). From this evolutionary sequence, we conclude that bipolarity in C-rich PNe begins on the AGB and that the dynamical ages of these PPNe are in fair agreement with theoretical ages for a 0.6 M hydrogen burning core star.  相似文献   

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