Spectroscopic Indications of an Internal Spiral Arm in the Galaxy
1956; Nature Portfolio; Volume: 178; Issue: 4548 Linguagem: Inglês
10.1038/1781458a0
ISSN1476-4687
Autores Tópico(s)Galaxies: Formation, Evolution, Phenomena
ResumoSPIRAL structure within our galaxy has been detected by three methods: (a) space-plotting of stellar associations1, (b) multiple structure in the H 21 cm. radiation2, (c) multiple structure in the interstellar lines of Ca II and Na I in distant stars3. The radio method (b) has the advantage over the two optical methods in that it will penetrate to the limits of the galaxy. On the other hand, the interpretation of the radio profiles for directions within 90° of the galactic centre is greatly complicated by the superposition of radiation from regions at very different distances which have the same angular velocity. By contrast, method (c) can reveal unambiguously the presence of one, two or more spiral arms within a light-path limited by a distant star. The limited light-paths used in method (c) are of advantage in the internal regions of the galaxy.
Referência(s)