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We present high-resolution 4.6micron CO spectra of the circumstellarenvironments of two RSGs that are potential SN progenitors: Betelgeuse and VYCMa. Around Betelgeuse, 12CO emission within 3arcsec follows a mildly clumpybut otherwise spherical shell, smaller than its 55arcsec shell in KIlambda7699. In stark contrast, 4.6micron CO emission around VY CMa iscoincident with bright KI in its clumpy asymmetric reflection nebula, within5arcsec of the star. Our CO data reveal redshifted features not seen in KIspectra of VY CMa, indicating a more isotropic distribution of gas punctuatedby randomly distributed asymmetric clumps. The relative CO and KI distributionin Betelgeuse arises from ionization effects within a steady wind, whereas inVY CMa, KI is emitted from skins of CO cloudlets resulting from episodic massejections 500--1000 yr ago. In both cases, CO and KI trace potential pre-SNcircumstellar matter: we conclude that an extreme RSG like VY CMa might producea Type IIn event like SN1988Z if it were to explode in its current state, butBetelgeuse will not. VY CMa demonstrates that LBVs are not necessarily the onlyprogenitors of SNe IIn, but it underscores the requirement that SNe IIn sufferenhanced episodic mass loss shortly before exploding.

Red supergiants as potential Type IIn supernova progenitors: Spatially resolved 4.6 micron CO emission around VY CMa and Betelgeuse