The density and mass of the spiral galaxy NGC 3198 have been studied as functions of the distance from the center of galaxy depending on its observed rotation curve. Calculation of density and mass at different radii of the galaxy NGC 3198 show that the central inner density ρ1(r) at r < r t (r t is the turn-off radius) is found to be constant ρ1 = 0.387 M o pc−3, while the density ρ2(r) of the outer region r > r t is much less than the inner region, which varies from 0.0187 M o pc−3 at r = 4 kpc to 0.00278 M o pc−3 at r = 30 kpc. On the other hand, the inner mass m1(r) at r < r t grows from 1.33 × 109 M o at r = 0.1 kpc to a mass of 8.539 × 109 M o at r = 4 kpc, while the outer mass m2(r) at r ≥ r t changes from 8.539 × 109 M o at the turn-off radius r t to 5.262 × 1010 M o at r = 30 kpc of the galaxy. Finally, the behavior of the calculated density and mass is consistent with other works.

R136 is a luminous object in the core of the 30 Doradus nebula. It is resolved into three main components (a, b, c). The brightest component (R136a) has been suggested to contain a dominant supermassive star (~ 2000 M©) or a group of very early O and WN stars. We have obtained spectra for the components in R136. There are at least two components showing Wolf-Rayet type spectral features: R136a 1 -WN4.5 and R136c-WN7. The OB population in R136a has an integrated spectral type of about 06 or earlier. Our new and improved data of R136a do not support the previously alleged periodic variation in the He il X4686 line velocity or the progressive redshifts in the higher Balmer absorption lines.

Expressions for the distributions of the density and mass of spiral galaxies have been derived for three different orientations of rotation curves with a turn over radius (r t). The central region of the galaxy is found to rotate as a rigid body with a constant density and with a central mass as a function of r 3. The density of the outer regions (r > r t) is found to vary inversely with the radius (r), and the corresponding mass is found to be a function of r 2. Galaxies with flat rotation curves at (r > r t) has less mass than that with rising up or lowering down rotation curves.

In this work we studied the dependence of the Cosmological parameters (the Hubble H(t) and deceleration q(t) parameters) on the red shift through the scale factor R(t), so we obtained two relations for the parameters. Assuming the scale factor as a function of time to the power α and α(t), we found other sets for the parameters H(t) and q(t). The derived relations for H(t) and q(t) coincides with the well-known relations for the parameters.

The density and mass of Spiral galaxy NGC 3672 has been studied as a function of the distance from the center of the galaxy. The mass of the three regions of the galaxy (nucleus, disk and halo) have been calculated and compared with other work. The total mass of NGC 3672 is found to be 1.22×10 11 M o at a radius of 23.7 kpc.