Jun-liang Zhao

Some statistical properties of spiral galaxies along the Hubble sequence

Abstract A statistical study has been made for the variations along the Hubble sequence, os such parameters as the degree of tightness of winding of spiral arm λ, the pitch angle μ, the flatness of the disk H/D25 and the thickness H along the Hubble sequence for 365 spiral galaxies published in A&Ap Supplement Series. The mean values of these quantities for the various Hubble types have been obtained for the first time. The results of the statistics show clearly 1) that the Hubble classification of spiral galaxies is one which has only a qualitative and statistical significance, and 2) that the dispersion relation in the density wave theory is valid for most spiral galaxies, i.e., the arms of most spiral galaxies satisfy the requirements of being tightly wound.

Studies of the open cluster M11. 4. The CM diagram, luminosity function and mass segregation

Using the relative proper motions and membership probabilities of 785 stars in the region of the open cluster M 11 (within 25′ of the cluster center), we found for the cluster, a distance of 1659 pc, and an age of (1.8−2.2)×108yr, a radius of about 24.5 pc, a luminosity mass of 4354 M⊙, and a virial mass of 5000 M⊙. A method is proposed to derive the present-day luminosity function from the observed luminosity function. Our analysis shows that, as an open cluster of intermediate age, the cluster stars show quite a clear mass segregation effect in space and that while mass segregation in the velocities does exist, it is not so obvious.

The luminosity and mass functions of the Virgo Cluster of galaxies

Abstract We study the luminosity and mass functions of the member galaxies in the central 6° of the Virgo Cluster. Membership is determined using velocity as criterion, while giving due consideration to the density distribution. Our study shows that the luminosity function for all the member galaxies follows the Schechter form, while for each spiral subtype, it is gaussian with the peak moving towards the fainter end and the width increasing along the sequence Sa→Sd. The mass function of the Virgo Cluster, like the mass function of stars, can be described by a power-law. Using the luminosity and mass functions, a discussion is made on the morphology of the cluster, mass segregation and the total luminosity of the region calculated.

Studies on the Coma cluster. III. The virial mass and kinematics

Abstract Using the radial velocity data on 414 galaxies in the Coma region of Kent and Gunn and the relevant results of statistical membership we determine the virial mass of the Coma cluster and discuss several issues in its kinematics. Our analysis shows that the Coma cluster has undergone some dynamical evolution and has not yet reached a sufficiently relaxed state. Judging by present available data, mass segregation in not marked. The virial mass of Coma determined from members of large membership probability is μ v = 2.63 × 10 15 μ⊙. The total luminosity is 1.45 × 10 13 L⊙, the mass-to-light ratio is 182 and the luminosity mass is μ L = 3.43 × 10 14 L ⊙.

A possible plasma jet in Comet Hale-Bopp

Abstract A large jet of Comet Hale-Bopp was observed in the B band on 1996-09-11 with the 1.56-m telescope and a Series 200 CCD camera.

Studies of the open cluster M 11. I. Proper motion measurement and membership determination

Abstract From PDS microdensitometer measurements of 10 plate pairs of the open cluster M 11 with epoch differences of 16–70 years taken with our 40 cm double astrograph, the relative proper motions of 872 stars in the cluster region are determined. 85% of these have accuracies better than 0.1 arcsec per century. The distribution parameters of stars with different magnitudes are found from a new mathematical model. The membership probabilities of the stars are calculated. 541 stars have membership probabilities higher than 0.7. The new approach of membership determination is shown to be not only theoretically rigorous, but also practically feasible, and more reasonable results can be obtained from its use. Some evidence is found for mass segregation in space and lesser evidence for mass segregation in velocity space.

Maximum likelihood estimation of the mean parallax and kinematic parameters of the Pleiades

Abstract A simultaneous, maximum-likelihood determination of the distance and kinematic parameters of the Pleiades is made. The results are: distance of the cluster d = 135.56 ± 0.72 pc, dispersion σ d = 7.66 ± 0.80 pc; space velocity V = 25.94 ± 0.13 km/s, dispersion σ v = 0.58 ± 0.09 km/s coordinates of the convergent point A = 101.95° ± 0.47°, D = −41.36° ± 0.29°.