Spectroscopy of very low mass stars and brown dwarfs in the Lambda Orionis star forming region - I. Enlarging the census down to the planetary mass domain in Collinder 69
A. Bayo, D. Barrado, J. Stauffer, M. Morales-Calderón, C. Melo, N. Huélamo, H. Bouy, B. Stelzer, M. Tamura and R. Jayawardhana
