Recent galactic and extra-galactic studies at Dwingeloo, The Netherlands.
1959; Institute of Physics; Volume: 64; Linguagem: Inglês
10.1086/107907
ISSN1538-3881
Autores Tópico(s)Historical Astronomy and Related Studies
ResumoThe 25-meter radio telescope at Dwingeloo, in continuous use now for over 2~3' years, has proved an excellent tool for detailed studies of the Galaxy and extragalactic systems. Results of an investigation of the central regions of the Galaxy are presented in another paper. Further 21-cm line investigations include a region of the Galaxy between R = 3.5 and 6 kpc, the Orion region, the association II Monocerotis, regions in Perseus, and six extragalactic nebulae. A large number of line profiles and drift curves are being obtained between 1 = 3500 and 100, b =+IOo to ~IOO, in order to investigate whether the expansion of the neutral hydrogen in the central parts of the Galaxy continues further outward. The ultimate aim of this investigation is a better value of the rotational velocity between R = 3.5 and 6 kpc, and a more detailed resolution of the spiral structure. In the Orion region, the work done at Harvard is~being repeated in more detail and in a larger region. Detailed correlation is found between dark clouds and intensity of 21-cm line radiation. In Perseus, individual clouds have been found at over 1000 pc from the galactic plane. The extragalactic nebulae M33, MIol, M81, IC 1613, NGC 6822 and NGC 4236 have been investigated in detail in a similar manner as M31 (Van de Hulst et al. 1957; Raimond and Volders 1957). The density distribution and rotation in M33 and MIol could be derived, from which it was possible to find the total amount of hydrogen (I& Mo and 3 X I& Mo) and the total mass (18 X I0~ Mo and 140 X I& Mo). The irregular nebula NGC 6822 is also rather bright, while the radiation from M81, IC 1613 and NGC 4236 is very faint. The hydrogen content of irregular nebulae is much higher than that of regular types. From a survey of the continuous radiation at 22 cm, the gross distribution of ionized hydrogen throughout the Galaxy was derived (Westerhout 1958). The total mass of ionized hydrogen is of the order of 4 X I0~ Mo. Values of the emission measure of many emission nebulae could be determined. A survey of the continuous radiation at 75 cm is partly reduced, and shows many interesting details in the Milky Way and the galactic corona. REFERENCES Raimond, E. and Volders, L. M. J. S. 1957, B. A. N. 14, 19. van de Hulst, H. C., Raimond, E. and van Woerden, H. 1957, B. A. N. 14, 1. Westerhout, G. 1958, B. A. N. `4, 215 and 261. Sterrewacht, Leiden, The Netherlands
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