Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aas...19312302a&link_type=abstract
American Astronomical Society, 193rd AAS Meeting, #123.02; Bulletin of the American Astronomical Society, Vol. 31, p.666
Astronomy and Astrophysics
Astronomy
Scientific paper
We have redetermined the total mass density near the sun using F and gK stars. Upgren's (1962,1963) data for F and gK stars in the direction of NGP; Bok & Basinski (1964) for F stars and McNeill (1989) for gK in the SGP have been used to redetermine the stellar density distribution perpendicular to the galactic plane. Recent determination of absolute magnitude of F stars (Houk et al., 1997); gK (Creze et al., 1989) and the absorption law by Knude (1996) is incorporated in the calculation. Exponential density distribution is assumed to represent the distribution up z=300 pc for F stars; z=500 pc for gK stars. There is an apparent asymmetric z distribution of these stars. This is interpreted as the sign of off-galactic plane position of the sun. Our calculation suggests that the sun is at z= 30-45 pc if F stars is used. Yamagata & Yoshi (1992) obtained z=40 pc based on the halo red stars. However, the sun's position is found at lower z (15-20 pc) if gK stars distribution is used. Combined Boltzmann-Poisson equation are solved analytically to find the total mass density (see Pham, 1997). Using the derived space-density and z-velocity-dispersion data obtained by Gomez et al. (1990) for F, by Flynn & Fuchs (1994) for gK, we obtained the total mass density of 0.150 and 0.115 Mo/pc3, respectively from F and gK. The value is checked against galaxy model and procedure of Bahcall (1984). Total mass density of 0.210 and 0.205 Mo/pc3 are derived from F and gK stars distributions respectively. Pham's method gives systematically lower total mass density as compared with that obtained by using Bahcall method. We note that the revised Pham's method is closer to the value of Oort limit. Taken this as face value we incline to propose that there is no missing mass; similar to that obtained by Pham (1997) based on Hipparcos F stars.
Arifyanto Mochamad Ikbal
Hidayat Bambang
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