On the Stability of a Magnetized Disk with a Massive Corotating Halo

Effects of magnetic fields on the stability of a differentially rotating disk are considered in the shearing sheet approximation.An explicit stability criterion is derived in terms of Toomre's Q value and the field strength.The combined effects of both magnetic fields and a corotating dark matter halo are briefly discussed.

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 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.

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.

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.

Inverse Correlation of the Ratios of S-Element Abundances in AGB Stars with Metallicity

In present study,the relations between the ratios of the heavy to light s-element(slow neutron captrue element)abundances and the average neutron exposure are calculated for the intrinsic and extrinsic AGB stars,respectively.In addition,the inverse correlation of these ratios with metallicity is also presented and interpreted quantitatively.This work is based on the evolution of the heavy element abundances of the intrinsic AGB stars,and the calculation on the heavy element overabundances of the extrinsic AGB stars.