HD 135485

Observations

Spectra of this star from 1956 displayed abnormally strong helium absorption lines, indicating a helium overabundance roughly ten times the normal level. A 1973 model atmosphere study, however, suggested a much lower helium abundance, probably less than double the solar proportion, and proposed the star might be a young, super-metal-rich object—a hypothesis later refuted. Further investigation revealed that the helium abundance is actually near normal, while the star exhibits unusually high metal abundances (elements heavier than helium), with general enrichment in all metals except nickel. The star has been assigned a stellar classification of B5 IIp, a peculiar B-type bright giant, though N. Houk and M. Smith-Moore (1978) found a more ordinary class of B3V. Its position on the HR diagram matches an evolved star near the blue horizontal branch (BHB), likely a core helium fusing star with a hydrogen fusing envelope. A noticeably larger nitrogen abundance suggests material from carbon-nitrogen processing has reached the surface, and the star may have undergone helium flashes in the core. A 2007 study found evidence of vertical stratification of nitrogen and sulfur, with abundances increasing toward the upper atmosphere—the first such observation of vertical metal stratification in a BHB star. The star may have formed in a metal-rich region of the Milky Way, which could explain some abundance anomalies. Under the BHB model, a 2001 study by Trundle and associates gives the star half the mass of the Sun, 120% of the solar radius, 68 times solar luminosity, and an effective temperature of 15,500 K. Other studies assume it is a main sequence star matching the B3V class, yielding an estimated age of 12 million years, a slow projected rotational velocity of 2 km·s−1, six solar masses, 2.7 solar radii, 417 times solar luminosity, and an effective temperature of 19,000 K.