paper

Re-visiting the case of R Mon: Is CO removed at R<20 au?

arXiv:1807.01893 · doi:10.1051/0004-6361/201731658

Abstract

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. We have re-evaluated the spectral type of R Mon using the available continuum data and UVES emission lines. We used a power-law disk model to fit previous 12 CO 1-0 and 2-1 interferometric observations and the PACS CO data to investigate the disk structure. Interferometric detections of 13 CO J=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. Our analysis confirms that R Mon is a B0 star. The disk model compatible with the 12 CO 1-0 and 2-1 interferometric observations falls short of predicting the observed fluxes of the 14<Ju<31 PACS lines; this is consistent with the scenario in which some contribution to these lines is coming from a warm envelope and/or UV-illuminated outflow walls. More interestingly, the upper limits to the fluxes of the Ju>31 CO lines suggest the existence of a region empty of CO at R<20 au in the proto-planetary disk. The intense emission of the HCO+ and CN lines shows the strong influence of UV photons on gas chemistry. The observations gathered in this paper are consistent with the presence around R Mon of a transition disk with a cavity about 20 au. This size is similar to the photoevaporation radius that supports the interpretation that UV photoevaporation is main disk dispersal mechanism in massive stars

arXiv comment16 pages, 14 figures, accepted in A&A

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