CO band emission from MWC349: I. First overtone bands from a disk or from a wind?

TL;DR

This study analyzes near-infrared spectra of MWC349, revealing that CO band emission likely originates from either a rotating disk with a bulge or a wind, with LTE conditions and specific kinematic properties.

Contribution

It is the first detailed modeling of CO overtone bands in MWC349, exploring different scenarios for their origin in a circumstellar disk or wind.

Findings

CO bands are formed under LTE at 3500-4000 K.

Gas has a column density of about 5×10^{20} cm^{-2}.

Both disk and wind models fit the spectra equally well.

Abstract

We observed the near infrared emission in the wavelength range 2.28-2.50 micron from the peculiar B[e]-star MWC349. The spectra contain besides the strong IR continuum the first overtone CO bands and most of the hydrogen recombination lines of the Pfund series, both in emission. We also modeled the spectra. The Pfund lines have a gaussian profile with a FWHM of ~100 km/s, and it turned out that their emission is in LTE and optically thin. To explain the CO bands, several scenarios were investigated. We found that the CO band heads are formed under LTE and that the gas must have a temperature of 3500 to 4000 K. The width of the 2 -> 0 band head indicates kinematical broadening of 50 to 60 km/s. We can obtain fits to the measured spectra assuming that the CO gas has a column density of 5 10^{20} cm^{-2} and is located either at the inner edge of the rotating circumstellar disk. In this case, the disk must have a bulge which partly blocks the radiation so that the observer sees only a sector on the far side where the radial velocities are small. Or the CO emission originates in a wind with gaussian line profiles. Both fits are of equal quality and satisfactory. In a third alternative where the fit is less convincing, the CO emission is optically thin and comes from an extended Keplerian disk.