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1.
We have imaged several known molecular (CO) outflows in H2 v=1-0 S(1) and wide-band K in order to identify the molecular shocks associated with the acceleration of ambient gas by outflows from young stars. We detected H2 line emission in all the flows we observed: L 1157, VLA 1623, NGC 6334I, NGC 2264G, L 1641N and Haro 4-255. A comparison of the H2 data with CO outflow maps strongly suggests that prompt entrainment near the head of a collimated jet probably is the dominant mechanism for producing the CO outflows in these sources. 相似文献
2.
A model of a first generation intermediate star of 5M
, with Z=0 has been considered. The model is at an advanced stage of its evolution and has a double shell burning. It burns helium in the inner shell, and hydrogen, via CNO cycle, in the outer shell.
=(log/log)
T
and
T
=(log/logT)
were computed allowing for the oscillations of the relative mass abundance of the reagents in nuclear reactions. Including
=(log/log)
T
and
=(log/logT)
of mean molecular weight and the effect of the oscillations of abundances due to nuclear reactions, stability was studied. Contrary to the results of the static calculations, we found that instability due to the excitation mechanism provided by the high temperature sensitivity of energy generation rate propagates up to the surface. Thus the model in question was found to be unstable against radial adiabatic pulsations, in its fundamental mode. 相似文献
3.
A. S. Baranov 《Celestial Mechanics and Dynamical Astronomy》1979,20(3):251-270
Periodic orbits of stars in axisymmetrical nearly spherical stellar systems have been investigated. Generating orbits have been found among periodic ones relating to the spherically-symmetrical field. The linear approximation appears to be insufficient for constructing periodic trajectories. Possible variants of the generating periodic solutions have been found, which give rise to disturbed periodic orbits in the second approximation.
, . - . , . , .相似文献
4.
A new telescope designed for high-resolution photography of the chromosphere is described. It is mounted in the open air on a 15-m tower and is provided with air suction shields to cool all surfaces exposed to the sun's rays. The best moments for photography are selected by a seeing monitor. The highest resolution so far attained is 0. 75 of arc, compared with a theoretical resolution limit at H of 0. 55. 相似文献
5.
6.
Evolutionary tracks of 0.9M
, 0.7M
and 0.6M
models for Population II stars have been computed in the post-red giant phase. The stars are initially composed of a helium core containing a mass fraction equal to 0.9 and of a hydrogen-rich envelope. They represent hypothetical remnants of stars after substantial mass loss in previous evolutionary phases or/and at the helium flash.u 0,9M
, 0,7M
0,6M
. , 90% , . , .Riassunto È stata calcolata per modelli di stelle di 0,9M
, 0,7M
e 0,6M
di Popolazione II l'evoluzione successiva allo stadio di gigante rossa. Inizialmente i modelli constano di un nucleo di elio contenente il 90% della massa totale e di un inviluppo idrogenico. Essi possono interpretarsi come i resti di stelle che abbiano perso una frazione di massa considerevole in fasi evolutive precedenti, o all'innesco violento dell'elio al centro. 相似文献
7.
We develop an automatic, computer controlled procedure to select and to analyze the Network Bright Points (NBPs) on solar images. These have been obtained at the Sac Peak Vacuum Tower Telescope by means of the Universal Birefringent Filter and Zeiss H filters, tuned, respectively, along the profiles of the H, Mg-b1, Na-D2, and H lines.A structure is identified as an NBP if at the wavelength H- 1.5 A its maximum intensity is greater than I + 3 and its area is greater than 1.5 arc sec2 at I + 1.5, where I is the mean value and the standard deviation of the intensity distribution on the image. Each detected NBP is then searched and confirmed in all the remaining 31 images at different wavelengths.For each NBP several parameters are measured (position, area, mean and maximum contrast, Dopplergram velocity, compactness, and so on) and some identification constraints are applied.The statistical analysis of the various parameter distributions, for NBPs present within an active region and its surroundings, shows that two types of NBPs can be identified according to the value of their mean contrast C
min the H- 1.5 Å image (C
m 0.1 type I, C
m> 0.1 type II). The type I NBPs (all occurring on the boundaries of the supergranular network) appear to be much more frequent (180/26) than the type II ones.The size A of type I NBPs is less than 1.0 arc sec for H/H wings but of the order of 1.2 arc sec for Na-D2 and Mg-bl. The mean contrast C
m is around the value of 10% along the Na-D2 and Mg-bl profiles and of 20% along the H/H wings.The C
m - A scatter diagrams show, for the photospheric radiation (h < 100 km), a narrow range of variability for C
min correspondence with a wide range for A. For radiation orginated at higher levels (h > 200 km), the C
m- A scatter diagrams seem to indicate, even if with a large variance, that the highest C
m's tend to correspond to the highest A values.The mean Doppler shift is close to zero for Na-D2 and Mg-bl lines but negative (downward motion) for H and H lines.The type II NBPs tends to be preferentially located in the neighbourhood of small, compact sunspots and their detectability is almost constant through all the 4 studied line profiles. No conclusions can be derived on the mean size, contrast and Doppler shift values because their distributions are too dispersed. The only positive information is that its C
m- A scatter diagram, in H and H wings, indicates a wide range of variability for C
m in correspondence with very narrow range of variability for A. 相似文献
8.
Paul S. Wesson 《Astrophysics and Space Science》1978,54(2):489-495
An exact solution of Einstein's equation is stated in which the density (), pressure (p), scale factorS and metric coefficients are functions of only one dimensionless self-similar variable,ct/R, wheret is cosmic time andR is a co-moving radial coordinate. The solution represents a cosmology that begins as a static sphere having R
–2 and evolves into an expanding model which is pressure-free and has a hierarchical type of density law ( R
–, approximately, with =a number, 02). It is suggested that this model should supersede the previous models of Wesson and other workers, since it appears to be the simplest cosmology for a hierarchy. 相似文献
9.
A CO J=4-3 map of the Orion-IRc2 region (size 80, beam 15) is presented. The outflow has a bipolar structure observed nearly pole-on. We interpret our observations in terms of an hierarchy of tubes where the fastest gas proceeds through the narrowest, innermost cone. The gas has an inhomogeneous temperature distribution and must be highly clumped. Most of the properties derived comply with the picture developed for the few known extreme high velocity outflows; however, this outflow contains exceptionally dense gas ( > 106 cm–3). 相似文献
10.
The reduction of observations of the O i 7773 triplet obtained at high spatial resolution (0.5) at two disk positions is described. Two sets of triplet profile data are presented at each disk position. One set represents data taken from 0.5 regions centered on the brightest granules, while the other set represents data taken from 0.5 regions centered on the cooler infalling intergranular material. 相似文献
11.
P. O. Lagage G. Oloffson S. Cabrit C. Cesarsky L. Nordh J. M. Rodriguez Espinosa 《Experimental Astronomy》1994,3(1-4):163-164
The region around the Herbig Ae/Be star LkH198 was imaged at 10m with the CAMIRAS camera at the Canada-France-Hawaii Telescope and the Nordic Optical Telescope. We discovered a deeply embedded companion 6 north of LkH198, which may be responsible for most of the far-infrared emission in the region and for driving the molecular flow. LkH198 appears point-like at our resolution (FWHM 1.3), excluding an extended envelope of transiently heated small grains as the dominant origin of the mid-infrared excess in that star. 相似文献
12.
The plot of the X-ray luminosity (in 0.5–4.5 KeV band and for Friedmann universe withq
0=+1) of the brightest X-ray QSO at each redshift against redshift shows that the X-ray luminosity increases more or less monotonically with redshift uptoz3. This result has been attributed to the selection effect known as the volume effect. When this selection effect is taken into account in the optical, radio and X-ray windows of the electromagnetic spectrum, a sample of the brightest X-ray QSO's is obtained which shows a small dispersion in X-ray luminosity: logL
1=46.15±0.25. The redshift-X-ray flux density plot for this sample gives slopes of both regression lines which agree, at a confidence level of 95% or greater, with the slopes expected theoretically if the redshifts of the QSO's are cosmological in nature. 相似文献
13.
Klaus P. Beuermann 《Astrophysics and Space Science》1973,20(1):27-38
A detailed analysis of interstellar measurements in the direction of the Gum nebula is carried out. The ionized region is shown to have an angular radius of 18° and appears to be bounded by a shell of neutral gas. The mean electron temperature deduced from radio-frequency absorption measurements is found to be 8500K. These parameters suggest that the nebula is the normal and possibly evolved Hii region of Pup and 2 Vel, rather than the fossil Strömgren sphere of the Vela supernova as suggested by Brandtet al. (1971). 相似文献
14.
We investigate the dynamics and evolution of coalescing neutron stars. The three-dimensional Newtonian equations of hydrodynamics are integrated by the Piecewise Parabolic Method on an equidistant Cartesian grid. The code is purely Newtonian, but does include the emission of gravitational waves and their back-reaction. The properties of neutron star matter are described by the equation of state of Lattimer and Swesty (1991). Energy loss by all types of neutrinos and changes of the electron fraction due to the emission of electron neutrinos and antineutrinos are taken into account by an elaborate neutrino leakage scheme. We simulate the coalescence of two identical, cool neutron stars with a baryonic mass of 1.6M
and a radius of 15 km and with an initial center-to-center distance of 42 km. The initial distributions of density and electron concentration are given from a model of a cold neutron star in hydrostatic equilibrium. We investigate three cases which differ by the initial velocity distribution in the neutron stars. The orbit decays due to gravitational-wave emission and after one revolution the stars are so close that dynamical instability sets in. Within 1 ms the neutron stars merge into a rapidly spinning (P 1 ms), high-density body ( 1014 g/cm3) with a surrounding thick disk of material with densities 1010 – 1012 g/cm3 and orbital velocities of 0.3-0.5 c. The peak emission of gravitational waves has a maximum luminosity of a few times 1055 erg/s and is reached for about 1 ms. The amplitudes of the gravitational waves are close to 3 10–23 at a distance of 1 Gpc and the typical frequency is near the dynamical value of the orbital motion of the merging neutron stars of 2 KHz. In a post-processing step, the rate of neutrino-antineutrino annihilation is calculated from the neutrino luminosities generated during the hydrodynamical simulations. We find the integral annihilation rate to be a few 1050 erg/s during the phase of strongest neutrino emission, which is too small to generate the observed bursts considering the fact that the merged object of about 3M will most likely collapse to a black hole within milliseconds. 相似文献
15.
Edison P. Liang 《Astrophysics and Space Science》1995,231(1-2):69-76
We review emission models of soft gamma-ray repeaters (SGRs) within the context of magnetized neutron star origins. Motivations for moderate field (1010–12G) versus ultrastrong field ( 5 × 1014G) neutron stars are considered. Implications for the astrophyiscal models are discussed. 相似文献
16.
Low-mass strange stars with a crust are investigated within the framework of the bag model. The crust, which consists of degenerate electrons and atomic nuclei, has a limiting boundary density
cr
, which is determined by the mass of the crust, and it cannot exceed the value
drip
= 4.3·1011 g/cm3, corresponding to the density at which neutrons drip from nuclei. For different values of
cr
in the low-mass range (M 0.1 M) we calculate several series of configurations: we find the dependence of the stellar mass M on the central density
c
for
cr
= const, with 109 g/cm3
cr
drip
, and for each series we determine the parameters of the configuration for which the condition dM/d
c
> 0 is violated. When the boundary density of the crust decreases to 109 g/cm3, the minimum mass of a strange star decreases to M
min 10-3 M, while the radius reaches 600 km. 相似文献
17.
Using archival ASCA observations of TT Arietis, X-ray energy spectra and power spectra of the intensity time series are presented for the first time. The energy spectra are well-fitted by a two continuum plasma emission model with temperatures 1 keV and 10 keV. A coherent feature at 0.643 mHz appeared in the power spectra during the observation. 相似文献
18.
The stars in the Main Sequence are seen as a hierarchy of objects with different massesM and effective dynamical radiiR
eff=R/ given by the stellar radii and the coefficients for the inner structure of the stars.As seen in a previous work (Paper I), during the lifetime in the Main SequenceR
eff(t) remains a near invariant when compared to the variation in the time ofR(t) and (t).With such an effectiveR
eff one obtains the amounts of actionA
c(M), the effective densities eff(M)=(M)3(M), the densities of action and of energy (or mean presures in the stellar interior)a
c(M),e
c(M), and the potential energiesE
p(M).The amounts of action areA
cM
k withk1.87 for the M stars,k5/3 for the KGF stars, andk1.83 for the A and earlier stars, representing very simples conditions for the other dynamical parameters. For instancek5/3 means a near invariant effective density eff for the KGF stars, while for such stars the mean densities and coefficients present the strongest variations with masses (M)M
–1.81, (M)M0.6.The cases for the M stars (e
c(M)M
–1) and for the A and earlier stars (betweena
c(M)=constant and eff(M)M
–1) and also discussed. These conditions for the earlier stars also represent reasonable mean values for the whole stellar hierarchy in the range of masses 0.2M
M25M
.With all this, one can build dynamical HR diagrams withA
c(M), Ep(M), eff
M
–p
, etc., whose characteristics are analogous to these in the photometrical HR diagram. A comparison is made betweenA
c(M) from the models here and the HR diagram with the best known stars of luminosity classes IV, V, and white dwarfs.The comparison of the potential energiesE
p(M)M
–p according to the stellar models used here and the observed frequency function (MM
–q (number of stars in a given interval of masses) from different authors suggests the possibility that the productE
p(M)(M) is a constant, but this must be confirmed with further studies of the function (M) and its fine structure.There are analogies between the formulation used here for the stellar hierarchy and other physical processes, for instance, in modified forms of the Kolmogorov law of turbulence and in the formulation used for the hierarchy of molecular clouds in gravitational equilibrium. Besides, the function of actionA
c(M) for the stars has analogous properties to the relations of angular momenta and massesJ(M) for different types of objects. The cosmological implications of all this are discussed. 相似文献
19.
GarcÍa R.A. Régulo C. Turck-Chièze S. Bertello L. Kosovichev A.G. Brun A.S. Couvidat S. Henney C.J. Lazrek M. Ulrich R.K. Varadi F. 《Solar physics》2001,200(1-2):361-379
Data recovered from the GOLF experiment on board the ESA/NASA SOHO spacecraft have been used to analyze the low-order low-degree solar velocity acoustic-mode spectrum below =1.5 mHz (i.e., 1n9,l2). Various techniques (periodogram, RLAvCS, homomorphic-deconvolution and RLSCSA) have been used and compared to avoid possible biases due to a given analysis method. In this work, the acoustic resonance modes sensitive to the solar central region are studied. Comparing results from the different analysis techniques, 10 modes below 1.5 mHz have been identified. 相似文献
20.
Giulio Calamai 《Astrophysics and Space Science》1971,10(1):165-177
A static relativistic theory of the stability of the equilibrium of an isentropic spherically-symmetric star is deduced from the properties of a functionu which is solution of a second-order differential equation, and which is related to the model by means of the formulau = m(v, c)/c, wherem is the mass-energy inside the coordinate volumev and c is the central mass-energy density.Work done in the Laboratorio Astrofisico di Frascati, Roma. 相似文献