| Description |
The formation mechanism of high-mass stars and the different
evolutionary phases involved in the process, still remain unclear.
We recently performed single-dish HCO+ and SiO observations at
millimetre wavelengths of a sample of high-mass star forming regions
in search of molecular outflows. Our results indicate
a decrease in the jet/outflow activity with the luminosity to mass ratio,
L/M, a distance-independent parameter considered to be an
estimate of time or evolutionary state. These findings are analogous
to what is found in the low-mass case, which suggests that high-mass
stars may form in a similar way to low-mass stars. However, uncertainties
such as the unknown inclination of the outflow axes and the poor
knowledge of HCO+ and SiO abundances call for more precise
measurements of the outflow mass loss rates to assess the variation
of this quantity with time and also associate them with the accretion
rate, a crucial parameter to understand high-mass star formation.
We therefore propose to image a suitably selected sub-sample of
the regions with outflows with PACS in the OI 63 micron line. According to
theory, this line can be related to the outflow mass loss rate, which can
thus be easily obtained. Combined with our single-dish outflow maps,
and with data from the Hi-GAL survey for a better estimate of the
luminosities and masses, we will calculate all the r^ant parameters to
assess the dependence of outflow rate on time for high-mass stars. We will
also observe the OI 145 micron line to check for possible opacity effects,
the CII 157 micron line to verify the presence of photo-dissociation
regions which could affect the OI emission, and a number of CO
transitions with both PACS and SPIRE to analyse the excitation conditions
of the outflows. |
