Vorontsov-Velyaminov rows: Straight segments in the spiral arms of galaxies

The phenomenon of rows-straight features in the spiral patterns of galaxies, which was discovered by Vorontsov-Velyaminov, is investigated. The rows are not artifacts; in several cases, they outline regular spiral arms almost over their entire lengths. The galaxies M 101, M 51, and a number of more distant spirals are used as examples to demonstrate major geometrical and physical properties of these structures. It is shown that the row lengths increase nearly linearly with distance from the disk center, and that the angle between adjacent rows is almost always close to 2 pi/3. The galaxies with rows generally belong to moderate-luminosity Sbc-Sc systems with low rotational velocities, regular spiral patterns (Grand Design), and an H I content normal for these types of galaxies. Two types of rows are shown to exist, which differ in thickness and appear to be evolutionarily related. The formation mechanism of the rows should probably be sought in the peculiar behavior of the gas-compression wave in spiral density waves. (C) 2000 MAIK "Nauka/Interperiodica".