TEMPERATURE AND INTERNAL KINEMATICS OF M8

A photoelectric Fabry-Pérot spectrometer is used to record the line profiles of Hα and [N ii] at 22 points in the nebula. The ratio of intensity Hα/[N ii] is used to derive an electron temperature distribution with values between 5700° and 9100° showing a peak at the centre of density. These temperatures are compared with the Hα Doppler temperatures to estimate excess velocities of mass motion. Together with the shifts of the Hα line centres, these lead to an evaluation of the velocity field in the nebula. It is suggested that the nebula consists of a core expanding at about ±10 km/sec-1 surrounded by a thick peripheral shell in which large scale mass motions are small. Non-thermal broadening suggesting turbulent velocities at about the speed of sound is observed in this shell and is attributed to small scale dynamic effects in a non-smooth density distribution. The effect of such expanding cores on heliocentric velocities of galactic Hii regions is discussed. © 1969 D. Reidel Publishing Company.