The mass-loss rates of red supergiants at low metallicity: detection of rotational CO emission from two red supergiants in the Large Magellanic Cloud

Using the PACS and SPIRE spectrometers on-board the Herschel SpaceObservatory, we obtained spectra of two red supergiants (RSGs) in theLarge Magellanic Cloud (LMC). Multiple rotational CO emission lines (J =6-5 to 15-14) and 15 H₂O lines were detected from IRAS05280-6910, and one CO line was detected from WOH G64. This is the firsttime that CO rotational lines have been detected from evolved stars inthe LMC. Their CO line intensities are as strong as those of theGalactic RSG, VY CMa. Modelling the CO lines and the spectral energydistribution results in an estimated mass-loss rate for IRAS 05280-6910of 3 × 10^-4 M⊙ yr^-1. Themodel assumes a gas-to-dust ratio and a CO-to-H₂ abundanceratio is estimated from the Galactic values scaled by the LMCmetallicity ([Fe/H] ˜ -0.3), i.e. that the CO-to-dust ratio isconstant for Galactic and LMC metallicities within the uncertainties ofthe model. The key factor determining the CO line intensities and themass-loss rate found to be the stellar luminosity.