Convection , pulsation and magnetic fields have all been suggested as mechanisms for the transport of mass and energy from the optical photosphere of red supergiants , out to the region where the stellar wind is launched .
We imaged the red supergiant Betelgeuse at 0.06 - 0.18 arcsec resolution , using e-MERLIN at 5.5–6.0 GHz , with a sensitivity of \sim 10 \mu Jy beam ^ { -1 } .
Most of the radio emission comes from within an ellipse ( 0.235 \times 0.218 ) arcsec ^ { 2 } ( \sim 5 \times the optical radius ) , with a flux density of 1.62 mJy , giving an average brightness temperature \sim 1250 K. This radio photosphere contains two hotspots of 0.53 and 0.79 mJy beam ^ { -1 } , separated by 90 milli-arcsec , with brightness temperatures 5400 \pm 600 K and 3800 \pm 500 K. Similar hotspots , at more than double the distance from the photosphere of those seen in any other regime , were detected by the less-sensitive ‘ old ’ MERLIN in 1992 , 1995 and 1996 and many exceed the photospheric temperature of 3600 K. Such brightness temperatures are high enough to emanate from pockets of chromospheric plasma .
Other possibilities include local shock heating , the convective dredge-up of hot material or exceptionally cool , low density regions , transparent down to the hottest layer at \sim 40 milliarcsec radius .
We also detect an arc 0.2–0.3 arcsec to the SW , brightness temperature \sim 150 K , in a similar direction to extensions seen on both smaller and larger scales in the infra-red and in CO at mm wavelengths .
These preliminary results will be followed by further e-MERLIN , VLA and ALMA observations to help resolve the problem of mass elevation from 1 to 10 R _ { \star } in red supergiants .