Faint emission lines and temperature fluctuations in M8

We present echelle spectroscopy in the 3500-10300 Angstrom range of the Hou rglass Nebula, which is embedded in the Galactic H II region M8. The data w ere obtained using the 2.1 m telescope at Observatorio Astronomico Nacional in San Pedro Martir, Baja California. We have measured the intensities of 274 emission lines, in particular 88 permitted lines of C+, N-0, N+, O-0, O +, Ne-0, S-0, S+, Si-0, Si+, and Si++, some of. them produced by recombinat ion only and others mainly by fluorescence. We have determined electron tem peratures and densities using different line intensity ratios. We derive th e He+, C++, O+, and O++ ionic abundances as well as-for the first time in a nebular object-the total O abundance from recombination lines; these nebul ar values are independent of the temperature structure of the nebula. We ha ve also derived abundances from collisionally excited lines for a large num ber of ions and elements; these abundances do depend on the temperature str ucture. Accurate t(2) values have been derived by comparing the C++, O+, an d O++ ionic abundances obtained making use of both collisionally excited li nes and recombination lines. A comparison of the solar, Orion Nebula, and M 8 chemical abundances is made.