A STUDY OF THE KINEMATICS OF THE LOCAL DARK CLOUDS

Authors
Citation
B. Ramesh, A STUDY OF THE KINEMATICS OF THE LOCAL DARK CLOUDS, Journal of astrophysics and astronomy, 15(4), 1994, pp. 415-443
Citations number
37
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Astronomy & Astrophysics
ISSN journal
0250-6335
Volume
15
Issue
4
Year of publication
1994
Pages
415 - 443
Database
ISI
SICI code
0250-6335(1994)15:4<415:ASOTKO>2.0.ZU;2-J
Abstract
Lack of reliable estimates of distances to most of the local dark clou ds has, so far, prevented a quantitative study of their kinematics. Us ing a statistical approach, we have been able to extract the average s patial distribution as well as the kinematical behaviour of the local dark clouds from their measured radial velocities. For this purpose, w e have obtained radial velocities for 115 southern clouds and used the data from the literature for the northern ones. In this paper we pres ent this new data, analyse the combined data and compare our results w ith those arrived at by earlier studies. The local clouds are found to be expanding at a speed of similar to 4 kms(-1) which is in general a greement with the estimates from optical and HI studies. However, it i s found that the kinematics of the local clouds is not described by th e model proposed for the local HI gas where a ring of gas expanding fr om a point gets sheared by the galactic rotation. Rather, the observed distribution of their radial velocities is best understood in terms o f a model in which the local clouds are participating in circular rota tion appropriate to their present positions with a small expansion als o superimposed. This possibly implies that cloud-cloud collisions are important. The spatial distribution of clouds derived using such a mod el is in good agreement with the local dust distribution obtained from measurements of reddening and extinction towards nearby stars. In par ticular, a region of size similar to 350 pc in diameter enclosing the Sun is found to be devoid of clouds. Intriguingly, most clouds in the longitude range 100 degrees to 145 degrees appear to have negative rad ial velocities implying that they are approaching us.