Bare Strange Stars Might Not Be Bare

It is proposed that the bare strange matter stars might not be bare,and the observed pulsars might be in fact the bare strange stars.As intensely magnetized strange matter stars rotate,the induced unipolar electric fields would be large enough to construct magnetospheres.This situation is very similar to that discussed by many authors for rotating neutron stars.Also,the strange stars with accretion crusts in binaries could act as x-ray pulsars or x-ray bursters.There are some advantages if pulsars are bare strange stars.

Halo Mass of Three-Dimension Milky Way

We emphasize the effects of several factors on halo mass for our Galaxy,such as the disk thickness,the local surface density,and the shape of the rotation curve.By fitting the observed rotation curve of our Galaxy with the five-component model,we deduce a halo with a mass of 6.62×10^(11)M■within 50kpc and a local density of 0.009M■pc^(-3).It is found that the realistic Galaxy needs only about half of the halo mass that the Galaxy with an inGnitesmally thin disk requires.

Luminosity Limit of Super-Eddington Accretion onto Black Holes

The luminosity limit is derived for the super-Eddington accretion by obtaining the self-similar solution.The maximum luminosity is about 4.0×10^(37) erg/s(M/M_(⊙))or so(significantly less than the Eddington luminosity)due to photon trapping although the accretion rate is super-Eddington.The radiation spectrum is found to be universal as F_(v) α v^(-1).

Disk Stability of the Milky Way Near the Sun

By solving Poisson's equation for logarithmic density disturbance in three-dimensional (3D) spiral galaxies, the disturbed potential can be given on the disk. Combining it with the corresponding dispersion relation, the local gravitational stability of our galaxy is discussed here. We have generalized the Toomre's stability criterion to the more realistic 3D galaxy models. The generalized Toomre's parameter Q near the sun is 2.08 or 2.20 for two or four armed spiral galaxy models, respectively.

Temperature Rise at the Edges of Dark Molecular Clouds

Two-fluid magnetohydrodynamic equations are applied to dark molecular clouds that are composed of neutrals mixed with minor charged particles,weakly ionized gas systems.The result shows the temperatures are higher at the cloud edges than at their inner regions,the cause of which is that the cloud potential,released as clouds contract particularly at their edges,along with some dissipated rotational kinetic energy is converted into thermal.The cloud contracting is due to the loss of the magnetic field that threads it through ambipolar diffusion.Nevertheless,without the support of the magnetic and the centrifugal forces in the direction of the magnetic Held assumed to be parallel to the cloud rotating axis,the cloud collapses in that direction when its mass is over the Jeans mass.

Abundance Analysis of HD131023

Based on high resolution and high signal-to-noise ratio spectra,we determine the chemical abundances of nearby star HD131023 by using the differential analysis.Abundances of total 24 elements are presented.Some heavy elements,such as Sr,Y,Ba,La,Nd,are found to be overabundant relative to the sun.

Abundances of the Neutron-Capture Elements in Metal-Poor Halo Star HD 126238

Using the new observations of several neutron-capture elements in metal-poor star HD 126238,combining a computer model and the method of least square,we accurately compute the component coefficients C_(1),C_(2),and C_(3).The results are C_(1)=2.52,C_(2)=0.26,C_(3)=0.31.Then employing the values of the component coefficients,we determine the relative contributions of the r-process and the s-process to the abundances of neutron-capture elements in the HD 126238,and predict the abundances of all the neutron-capture elements in this metal-poor star.The predictions agree well with the observations.

Generation of High Speed Particles in Herbig--Haro Flow Regions

A mechanism is presented for generating high speed particles in Herbig-Haro flow coming from accretion disks associated with protostars.The disks are threaded with weak magnetic field lines,in which the magnetorotational instability results in magnetohydrodynamic turbulence.Then the turbulent waves accelerate the thermal particles out of the accretion disks to a few hundred kilometres per second,forming the high speed particles of optical jets in star-forming regions.

A New Method to Determine the Thickness of Spiral Galaxies:Apply to M31

A new method is presented to determine the thickness of spiral galaxies.Based on the rigorous solution of the Poisson equation for logarithmic density disturbance in three-dimensional spiral galaxies,we have derived an accurate dispersion relation for the stellar and gaseous disk with a finite thickness.From this relation,a new method is put forward here for determining the thickness of galaxies.We apply this way to M31 and get the thickness of about 0.7kpc,which is in good agreement with the previous results.

On Three-Dimensional Spiral Galaxies

Density waves in 3D spiral galaxies are studied.In order to eliminate the forbidden region near the corotation in the grand-design galaxies,we assume that the perturbation satisfies the stable condition Q(r)>1 over all the disk except that at the corotation.Then,a new method is put forward here to determine some basic parameters of spiral galaxies.We apply it to our Galaxy,and the results are in good agreement with the previous results.

Group Velocity of the Density Waves in Galactic Disks

This letter is emphasized on the discussion of the group velocity of disturbed galactic density waves(GDW),which is one of the two most insurmountable problems in the density waves theory.In our calculation,we find that the galactic thickness has an important effect on the GDW.The dynamic time scale of GDW in our three-dimensional model can be prominently prolonged,from 36%to 60%contrasting to that of two-dimensional galactic model.However,it is still less than the lifetime of our Galaxy,which means that it is necessary to seek some other physical mechanisms to excite and sustain the GDW.

A Quasar Spectrum with a Multiplet-Like Structure Caused by the Raman Effect

It has been shown that if a photon is scattered by a relativistic electron in a strong magnetic field, this may cause the Raman effect due to a transition between Landau levels. We study the possibility that this quantum effect occurs in some compact objects. We find that there is a multiplet-like structure in the quasi-stellar object (QSO)1303+308 spectrum, which is consistent with that expected by the Raman effect. It indicates that there might be a magnetic field strength about 5 × 10^(6)G in the environment of this QSO at redshift 1.7175.

Dependence of Spiral Galaxy Distribution on Viewing Angle in RC3

The normalized inclination distributions are presented for the spiral galaxies in RC3.The results show that,except for the bin of 81°-90°,in which the apparent minor isophotal diameters that are used to obtain the inclinations are affected by the central bulges,the distributions for Sa,Sab,Scd and Sd are well consistent with the Monte-Carlo simulation of random inclinations within 3-σ and Sb and Sbc almost,but Sc is different.One reason for the difference between the real distribution and the Monte-Carlo simulation of Sc may be that some quite inclined spirals,the arms of which are inherently loosely wound on the galactic plane and should be classified to Sc galaxies,have been incorrectly classified to the earlier ones,because the tightness of spiral arms which is one of the criteria of the Hubble classification in RC3 is different between on the galactic plane and on the tangent plane of the celestial sphere.Our result also implies that there might exist biases in the luminosity functions of individual Hubble types if spiral galaxies are only classified visually.