S. Pérez-Martínez 1, B. Lefloch 1, J. Cernicharo 1, P. Cox 2, F. Boulanger 2, D. Cesarsky 2, F. Najarro 1, & E. González-Alfonso 1
1 CSIC, Instituto de Estructura de la Materia, Dpto. Fisica Molecular, C/Serrano 121, 28006 Madrid, Spain
2 IAS, Orsay, France
We present a detailed study of the Trifid Nebula with all the ISO instruments.
In addition to the infrared maps and spectra we have observed the Trifid in
the emission of CO (J=1-0, 2-1, 3-2), HCO+ (J=1-0), CS (J=2-1, 3-2),
SiO (J=2-1, 3-2, 5-4), and the isotopes of CO. A full map at 1.3 mm has
been also obtained with the MPI bolometer installed at the 30-m IRAM
radiotelescope. The infrared data consist in four large scale maps (18'x18')
with ISOCAM in different filters with a pixel size of 6 arcsec and one
large map with a pixel of 3 arcsec. In addition, 8 fields have been observed
with ISOCAM-CVF and pixel size of 3 arcsec. Maps with ISOPHOT at 60, 100 and
200 
m have been also obtained. The LWS spectrometer has been used to
obtain the 43-197 m spectrum at selected positions of the Trifid.
One cometary globule associated to an optical jet has been observed with
ISOCAM with a pixel size of 1.5 arcsec in different filters. SWS and LWS
spectra towards it have also been obtained.
In this contribution we report prelimary results concerning the star formation activity in the Trifid Nebula. This HII region is produced by an O7V star (see poster by Cernicharo et al.) which has not evaporated yet the cocoon in which it was formed. Around the HII region, just at the interface region between the neutral and ionized gas we have found several condensations of very cold dust which are associated with strong molecular emission. The molecular lines present wings resulting from the shock-wave associated to the ionization front. In one of these globules we have detected strong SiO emission extending in velocity over more than 50 kms-1. We present a model in which these clumps have been produced by the interaction of the UV photons from the central star and the parent molecular cloud. The gas compressed by the shock-wave is (or has) collapsed to produce the observed clumps in which a second generation of stars will form. These clumps are much more massive than those found in dark molecular clouds associated to class 0/1 sources and will probably produce massive stars or clusters of stars of intermediate mass.