An Evolved Disk Surrounding the Massive Main-Sequence Star MWC 297?

We present the results of the interferometric observations of the circumstellar disk surrounding MWC 297 in the continuum at 230 GHz (1.3 mm) and in the (J=2-1) rotational transitions of ¹²CO,¹³CO, and C¹⁸O using the Submillimeter Array. At a distance of 250 pc, MWC 297 is one of the closest, young massive stars (M_*~10 M_solar) to us. Compact continuum emission is detected toward MWC 297 from which we estimate a disk mass (gas+dust) of 0.07 M_solar and a disk radius of <=80 AU. Our result demonstrates that circumstellar disks can survive around massive stars well into their main-sequence phase even after they have become optically visible. Complementing our observations with the data compiled from the literature, we find the submillimeter dust opacity index β to be between 0.1 and 0.3. If the emission is optically thin, the low value of β indicates the presence of relatively large grains in the disk, possibly because of grain growth. We do not detect any CO emission associated with the continuum source. We argue that the ¹³CO emission from the disk is likely optically thin, in which case we derive an upper limit to the gas mass that implies significant depletion of molecular gas in the disk. The mass of this disk and the evolutionary trends observed are similar to those found for intermediate-mass Herbig Ae stars and low-mass T Tauri stars.