The Rotation, Mass Distribution, and Mass of NGC 5055.

The rotation-curve of NGC 5055 (M63) was obtained from measures of the Ha emission line on spectra taken at the pflme focus of the 82-inch telescope with a long slit The accuracy of the measures is discussed. The rotation-curve extends more than 3' from the center and reaches well past the turnover point An integral equation was solved for the mass distiibution under the assumption that the equidensity surfaces are similar spheroids with c/a = 1/15. The total mass is 7.6 x 1010 or 5.5 X 1010M0, for distances of the galaxy of 10.3 X 106 pc or 7 4 X 106 pc, respectively (the distance is not known accurately). The corresponding mass-to-light ratio from the photographic magnitude, for the whole galaxy is 2.0 or 2 5 The mass-to-light ratio is about four times as high as this in the inner part of the galaxy. Beyond about 20" from the center, the mass-to-light ratio falls off gradually out to a value of 3.3 or 4.7 for the two distances (from the photographic luminosity) at 1' from the center, outside of which there is no photometry.