摘要：Context.To our knowledge, R Mon is the only B0 star in which a gaseous Keplerian disk has been detected. However, there is some controversy about the spectral type of R Mon. Some authors propose that it could be a later B8e star, where disks are more common.Aims.Our goal is to re-evaluate the R Mon spectral type and characterize its protoplanetary disk.Methods.The spectral type of R Mon has been re-evaluated using the available continuum data and UVES emission lines. We used a power-law disk model to fit previous12CO 1 →0 and 2 →1 interferometric observations and the PACS CO data to investigate the disk structure. Interferometric detections of13COJ= 1 →0, HCO+1 →0, and CN 1 →0 lines using the IRAM Plateau de Bure Interferometer (PdBI) are presented. The HCN 1 →0 line was not detected.Results.Our analysis confirms that R Mon is a B0 star. The disk model compatible with the12CO 1 →0 and 2 →1 interferometric observations falls short of predicting the observed fluxes of the 14 31 CO lines suggest the existence of a region empty of CO atR≲ 20 au in the protoplanetary disk. The intense emission of the HCO+and CN lines shows the strong influence of UV photons on gas chemistry.Conclusions.The observations gathered in this paper are consistent with the presence of a transition disk with a cavity ofRin≳ 20 au around R Mon. This size is similar to the photoevaporation radius that supports the interpretation that UV photoevaporation is main disk dispersal mechanism in massive stars
