The Rotation of the Spiral Nebula Messier 33.

Abstract

view Abstract Citations (67) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Rotation of the Spiral Nebula Messier 33. Mayall, N. U. ; Aller, L. H. Abstract The investigation is based on radial velocity observations of 25 bright-line condensations well dis- tributed over the spiral (P1. I), and upon several long exposures that record the spectrum of the unre- solved nebulosity of the nuclear region. As preliminary steps in the derivation of the relation between rotational velocity and nuclear distance, the velocity of the system is found to be - 167 ± 5 km/sec from three different groups of the data; also, the inclination to the line of sight of the principal plane of the spiral is found to be 330 from long-exposure direct photographs on 6~ X 8~-inch plates taken with the Crossley reflector. By using these results, together with the assumption of simple circular motion in the plane, rotational velocities of low precision (the linear dispersion of the spectra is 304 A/mm at X 395o) are first obtained for the individual condensations (Fig. i) and then combined to give a first approximation to the rotational-velocity-curve (Fig. 2). The latter may be briefly described as follows: the main body of the spiral, some i 8' in radius, appears to rotate almost like a solid body (rotational velocity increases fair- ly uniformly with distance), while the outer parts, represented by a zone having least and greatest radii of i8' and 30', respectively, appear to rotate like a planetary system (rotational velocity decreases with dis- tance). The transition between these two types of motion occurs in the general vicinity of i6' (iooo parsecs) from the center, at which distance the rotational velocity attains a maximum of approximately 120 km/sec. The observations define fairly well the character of the motion out to the extreme limits of the spiral (30', or nearly 2000 parsecs) shown on the photographs. Comparison of the results for these most distant regions of M 33 with similar ones for the solar neighborhood of the Galaxy strengthens the current hypothesis that the sun is located at a considerable distance from the main body of our own stellar system. I. INTRODUCTIO Publication: The Astrophysical Journal Pub Date: January 1942 DOI: 10.1086/144369 Bibcode: 1942ApJ....95....5M full text sources ADS | data products NED (37) SIMBAD (33)