Red supergiants in the LMC - I. BVRIJHK photometry, magnitudes and intrinsic colours

(BV)J(RI)C observations for 185 and additional JHK observations for 53 red supergiant candidates in the Large Magellanic Cloud (LMC) are presented. The data have been reduced discussing carefully the dependence of effective wavelengths on the spectral energy distribution of the star, which is very strong especially for the Cousins R band. Non-linear colour dependences of transformation coefficients for the V magnitude and R — I colour have been taken into account. The mean error of the BVRIdata is 0.03 to 0.04 mag, while that of theJHKobservations is 0.02 mag. The data will be available at the Centre de Données astronomiques de Strasbourg (CDS). Because of the broad-band effects mentioned above, the reddening lines are strongly dependent on the spectral energy distributions of the stars. Infrared reddening lines are only slightly affected, as the effective wavelengths of these bands are almost constant. Intrinsic colours and absolute magnitudes have been derived applying new investigations of the foreground and internal reddening of the LMC. The (B—V)0 and (V—R)0 colours are redder than for galactic red supergiants, while for (R—I)0 (J—H)0 and (H—K)0 no differences have been found. With luminosities resembling those of galactic lab or la supergiants, the LMC objects are not more luminous than their galactic counterparts.