Combining the luminosity functions of main sequence stars in 3 associations and 22 open clusters, the initial luminosity function and mass function for these clusters are derived. For stars of m > 0.6 m ⊙ , they are well consistent with those for the field stars.

We study the luminosity and mass functions of open clusters using the data published by the United States Navel Observatory to figure out the relationships between these functions and the cluster ages. Slope ranges of the luminosity (dlogN/dMv) and mass function (-dlogN/d(log m/m@)) are 0.09-0.52(avg.=0.26, var.=0.01), 0.43-5.49(avg.=1.7, var.=0.63) respectively. These large ranges do not support the mass function is universal, but the function is time dependent. Despite of the poor relationship between the luminosity function and the cluster age, we obtain a good relationship in the mass function. We can understand this good relationship with a viewpoint of stellar evolution. We do age analyses in terms of the metal abundance and the number density of the open clusters. We get the fact that the less metal abundances and the less number densities, the more steep in the slopes of the mass function.

The Wielen dip over the ragne of 6 < M υ < 9 in the luminosity function (LF) for the solar neighborhood stars could be explained by the combination of two different IMFs which yields the age of 13 billion years of the solar neighborhood. This smaller age than the Galactic age, 15 billion years indicates the slow collapse model of the Galaxy, solving the G-dwarf problem. Two different IMFs suggest two different mechanisms for star formation in the solar neighborhood.

Dynamical conditions for the fronts around the Yellow Sea Cold Water Mass, were investigated by means of the oceanographical data and simple numerical experiment. The coastal front developed along the coast inside the Yellow Sea and distinguished the Yellow Sea Cold Water Mass from the coastal water is attributed to the predominant tidal mixing near the coast. On the other hand the southern part of the front of the cold water mass would be explained a a part of the extention of a western boundary current which flows into the Cheju Channel.

From the kinematically unbiased sample of halo stars, the local mass density of halo dwarfs is estimated as 6.0 ∼ 6.3 × 10 − 4 m ⊙ / p c 3 by adopting a color-magnitude relation and a mass-luminosity relation. The derived halo mass density is not much different from the results of previous studies, which were derived from the kinematically biased sample of halo stars. Therefore it is confirmed that the local mass density of halo stars is far less than that required by Ostriker-Peebles to stabilize the galactic disk against barlike instabilities.

We derived initial mass functions (IMF) of massive stars in three different regions of spiral arms within 2.5kpc from the sun. The derived IMF slope β β of Local arm stars is found to be −2.09∼−2.06 −2.09∼−2.06 , very close to that of Bisiacchi et al. (1983). For Sagittarius-Carina arm stars β β ranges from -1.77 to - 1.72 which is close to that of overall stars given by Germany et al. (1982). Possible causes inducing the regional difference in IMFs are discussed.

Under the context of Stein's linear theory of stellar models, the luminosity-effective temperature relationship is derived for contracting pre-main sequence stars which are losing mass, according to the empirical formula, given by Reimers (1975). The effects of mass loss on their evolution are investigated by calculating evolutionary tracks of 1. 1.5M⊙ 1.5M⊙ , 5M⊙ 5M⊙ , and 10M⊙ 10M⊙ , stars. Our calculations reveal that the effects of mass loss show up in the radiative equilibrium stage of the evolution. It is found that an increase of mass loss rate leads to delay the onset of radiative equilibrium, thus resulting in under-luminous main sequence stars. It is also noted that the mass loss prolongs the pre-main sequence life time. Detailed results of the calculations are discussed.

N-logM diagrams of 29 open clusters are obtained by, using observational data and theoretical evolutionary track of stars on M_(bol)-T_(eff) diagram. A certain relation between the forms of N-logM diagrams and their ages are found. And a temporary interpretation is given for it.

The well observed 8 open clusters, NGC 6530, 2264, 654, 129, 2168, Pleiades, Praesepe and Hyades were selected on the basis of photometric observation and proper motion study. The luminosity functions (LF) and mass functions (MF) of these clusters are different with cluster age and they could be divided into three age groups (t< 10 7 yrs, 10 7 10 8 yrs, 10 8 10 9 yrs). From these LF's and MF's, the mean LF and MF of the open clusters are derived and these functions suggest the time-dependent initial mass function (IMF) and the variation of observed MF with cluster age.

The present day mass functions of main sequence stars in the well observed open clusters, Hyades, Praesepe, Pleiades, NGC 654 and NGC 6530 arc derived and compared with those computed from the model of time-dependent initial mass function and star formation rate. The agreements between the observed and computed present day mass functions suggest the importance of fragmentation process at the early phase and fragment interaction at the later phase of cluster evolution. This process of star formation is different from that related to the evolution of the solar neighborhood, and also could explain the lack of low mass stars observed in some open clusters.

According to the star formation rate and metal enrichment rate given by the disk-halo model of Lee and Ann (1981), the two different forms of time-dependent initial mass function (IMF) and the present day mass function (PDMF) of nearby stars have been examined. It was shown that the constraint for the initial rapid metal enrichment requires the time-dependence of IMF at the very early phase ( t ≲ 5 × 10 8 yrs) of the solar neighborhood. The computed PDMF's show that the PDMF is nearly independent of any specific functional form of IMF as long as the latter includes a Gaussian distribution of log m. This result is due to the very small fractional mass ( × 5 of stars formed at the very early period during which the IMF is time-dependent. The computed PDMF suggests the presence of more numerous low mass stars than shown in Miller and Scalo's (1979) PDMF, supporting the possibility of the existence of low-velocity M dwarfs. According to the number distribution of stars with respect to [Fe/H], the mean age of these low mass star must be very old so as to yield the mean metal abundance ¯ [ F e / H ] ≈ − 0.15 for the stars in the solar neighborhood.

Weibull analyses given to the initial mass function (IMF) deduced by Miller and Scalo (1979) have shown that the mass dependence of IMF is an exp [ − α m ] - form in low mass range while in the high mass range it assumes an exp [ − α √ m ] / √ m -form with the break-up being at about the solar mass. Various astrophysical reasonings are given for identifying the exp [ − α m ] and exp [ − α √ m ] / √ m with halo and disk star characteristics, respectively. The physical conditions during the halo formation were such that low mass stars were preferentially formed and those in the disk high mass stars favoured. The two component nature of IMF is in general accord with the dichotomies in various stellar properties.