The star VY CMa is a late-type M supergiant with many peculiarities , mostly related to the intense circumstellar environment due to the star ’ s high mass-loss rate .
Claims have been made that would suggest this star is considerably more luminous ( L \sim 5 \times 10 ^ { 5 } L _ { \odot } ) and larger ( R \sim 2800 R _ { \odot } ) than other Galactic red supergiants ( RSGs ) .
Indeed , such a location in the H-R diagram would be well in the “ Hayashi forbidden zone ” where stars can not be in hydrostatic equilibrium .
These extraordinary properties , however , rest upon an assumed effective temperature of 2800-3000 K , far cooler than recent work have shown RSGs to be .
To obtain a better estimate , we fit newly obtained spectrophotometry in the optical and NIR with the same MARCS models used for our recent determination of the physical properties of other RSGs ; we also use V - K and V - J from the literature to derive an effective temperatures .
We find that the star likely has a temperature of 3650 K , a luminosity L \sim 6 \times 10 ^ { 4 } L _ { \odot } , and a radius of \sim 600 R _ { \odot } These values are consistent with VY CMa being an ordinary evolved 15 M _ { \odot } RSG , and agree well with the Geneva evolutionary tracks .
We find that the circumstellar dust region has a temperature of 760 K , and an effective radius \sim 130 AU , if spherical geometry is assumed for the latter .
What causes this star to have such a high mass-loss , and large variations in brightness ( but with little change in color ) , remains a mystery at present , although we speculate that perhaps this star ( and NML Cyg ) are simply normal RSGs caught during an unusually unstable time .