Stars are a product of their time in the most literal sense. When they formed determines their size, chemical composition and how long they are destined to live. The newest stars have a vast array of elements and a high metallicity. They are also on the smaller side of stars and will live for quite a long time. The first stars formed in a galaxy are massive; having nothing but hydrogen and helium to form from they quickly fuse through their lives before becoming supernovae which will provide the debris for later stars. It is possible to examine the elements present in a star by looking at its spectrum as each element produces its own unique spectral output.
And this is exactly what astronomers have been doing. BD+44 493 is the brightest class II star in the milky way. It was formed directly from an original metallicity 0 star and so only contains a few elements greater in mass than helium. The Hubble telescope was able find the spectra of phosphorus and sulphur, two elements that had never been seen in this type of star before. Working backwards an upper limit can be put on the mass of the star that produced these elements. The current estimation is about twenty times the mass of the Sun but as the method becomes more refined, the prediction will become more precise.