A Keplerian Gaseous Disk around the B 0 Star R Mon

We present high-angular resolution observations of the circumstellar disk around the massive Herbig Be star R Mon (M * ∼8 M ⊙) in the continuum at 2.7mm and 1.3mm and the 12 CO 1→0 and 2→1 rotational lines. Based on the new 1.3mm continuum image we estimate a disk mass (gas+dust) of 0.007 M ⊙ and an outer radius of <150 AU. Our CO images are consistent with the existence of a Keplerian rotating gaseous disk around this star. Up to our knowledge, this is the most clear evidence for the existence of Keplerian disks around massive stars reported thus far. The mass and physical characteristics of this disk are similar to those of the more evolved T Tauri stars and indicate a shorter timescale for the evolution and dispersal of circumstellar disks around massive stars which lose most of their mass before the star becomes visible. Subject headings: Radio continuum: stars – Circumstellar matter – Stars: individual (R Mon) – Stars: pre-main sequence 1. INTRODUCTION Herbig Ae/Be stars (HAEBE) are intermediate mass (M∼2–10 M ⊙) pre-main sequence objects. A big theoretical and observational effort has been done in recent years for the understanding of the disk occurrence and evolution in HAEBE. For Herbig Ae and late-type Be stars (spectral type later than B7) (hereafter HAE), it is generally accepted the presence of disks similar to those associated with T Tauri stars (TTs). The association of the more massive early Be stars (HBE) with disks is more uncertain. Evidence for the existence of dusty and gaseous circumstellar disks around some HBE exists at optical, NIR and mid-IR wavelengths (Meeus et al. 2001,Vink et al. 2002, Millan-Gabet et al. 2001, Acke et al. 2005). Furthermore, disks around HBE seem to have different geometry from those around HAE and TTs. While most HAE and TTs have flared disks, HBE seem to have (if any) geometrically flat disks (see e.g. Acke et al. 2005). However, the direct detection of cir-cumstellar disks around HBE at millimeter wavelengths has remained elusive until recently. We carried out a high sensitivity search for circum-stellar disks around HBE with the aim of studying the frequency and timescales of disks in these massive stars. We observed a sample of HBE in the continuum at mm-and cm-wavelengths using the PdBI and VLA (Fuente et al. 2001; Fuente et al. 2003, hereafter Paper I) and detected two dusty disks around MWC …