log(g) = 1.0. This change means that in a few decades the star has passed through a region of instability on the H–R diagram where no stars are observed, an evolutionary change that has not been observed in any other star. Elemental abundances derived from the spectrum indicate approximately solar metallicity, although some elements are enhanced due to the evolutionary state of HR 8752. Evolutionary state Prior to 1973, HR 8752 was a cool yellow hypergiant with an early G spectral type. Following a dramatic shedding of its outer layers, it has now jumped to mid-A hypergiant and is not expected to return to its cool state. Models of a ZAMS star show it crossing the "yellow evolutionary void" instability region first towards cooler temperatures, then later back towards hotter temperatures. The yellow evolutionary void is named because very few stars are found in that part of the H–R diagram. This is likely to be because the evolution of stars with such parameters is extremely rapid, perhaps even almost instant in astronomical terms. The first crossing of the yellow evolutionary void is very rapid but the star does not experience major instability. The second crossing, returning to hotter temperatures after a time as a yellow hypergiant, involves crossing a region, or possibly two regions, where the star experiences major instability, expected to show as episodes of strong mass loss. HR 8752 has crossed the first of the two major zones of instability and is expected to migrate to even hotter temperatures over a timescale on the order of a thousand years. Based on its current observed state, HR 8752 is estimated to now have left from an initial and is likely to become a relatively low-luminosity luminous blue variable before evolving further into a Wolf–Rayet star. The ultimate fate of all massive stars is a core collapse and some sort of supernova explosion. Below about this is expected to occur as a type II supernova from a red supergiant progenitor. More massive stars evolve into Wolf–Rayet stars before exploding as a type Ib or Ic supernova. For some intermediate range of masses, stars are thought to undergo core collapse at the yellow hypergiant or LBV stage of their lives, resulting in a type IIb or perhaps IIn supernova. HR 8752 may be such a star, and may never make it beyond its current evolutionary state before exploding. Possible binary HR