Context :

Aims : Red supergiants ( RSGs ) are among the most luminous of all stars , easily detectable in external galaxies , and may ideally serve as kinematic tracers of Galactic structure .
Some RSGs are surrounded by circumstellar envelopes detectable by their dust and molecular and , in particular , maser emission .
This study consists of a search for maser emission from silicon monoxide ( SiO ) toward a significant number of RSGs that are members of massive stellar clusters , many of which have only recently been discovered .
Further , we aim to relate the occurrence of maser action to properties of the host stars .

Methods : Using the IRAM 30 meter telescope , we searched for maser emission in the J = 2 - 1 rotational transition within the first vibrationally excited state of SiO toward a sample of 88 RSGs .

Results : With an average rms noise level of 0.25 Jy , we detected maser emission in 15 % of the sample , toward most of the sources for the first time in this transition .
The peak of the emission provides accurate radial velocities for the RSGs .
The dependence of the detection rate on infrared colors supports a radiative pumping mechanism for the SiO masers .

Conclusions :