The oscillation modes of the beta Cephei star in HD 92024 in the open cluster NGC 3293

The primary star of the binary HD 92024 is a prominent beta Cephei variable; three oscillation frequencies are known, it is an eclipsing binary component and has cluster membership (NGC 3293). Towards asteroseismic inferences of the star's three known oscillation frequencies, we use photometry and spectroscopy to find that f_1=5.6400 ;c d-1, f_2=7.1624 ;c d-1 and f_3=6.6584 ;c d-1 are modes of degree l=2, 4 and 2 respectively, all with m!=0. We also find that by combining pulsational information from several spectral lines, we suppress the noise and improve the mode-identification process. In conclusion, HD 92024 is a key object to be subjected to a seismic analysis. We report on observational results obtained for 78 objects originally classified as bona-fide or candidate gamma Doradus stars. For the southern objects, we gathered echelle spectra with the CORALIE spectrograph attached to the Euler telescope in 1998-2003 and/or Johnson-Cousins B,V,I_c observations with the MODULAR photometer attached to the 0.5-m SAAO telescope in 1999-2000. For the northern objects, we obtained Geneva U,B,B_1,B_2,V,V_1,G observations with the P7 photometer attached to the 1.2