Nucleosynthetic signatures of the first stars The chemically most primitive stars provide constraints on the nature of the first stellar objects that formed in the Universe; elements other than hydrogen, helium and traces of lithium within these objects were generated by nucleosynthesis in the very first stars. The relative abundances of elements in the surviving primitive stars reflect the masses of the first stars, because the pathways of nucleosynthesis are quite sensitive to stellar masses. Several models have been suggested to explain the origin of the abundance pattern of the giant star HE 0107-5240, which hitherto exhibited the highest deficiency of heavy elements known. Here we report the discovery of HE 1327-2326, a subgiant or main-sequence star with an iron abundance about a factor of two lower than that of HE 0107-5240. Both stars show extreme overabundances of carbon and nitrogen with respect to iron, suggesting a similar origin of the abundance patterns.

known as stellar nucleosynthesis. Nuclear fusion reactions create many of the lighter elements, up to and including iron and nickel in the most massive Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons (protons and neutrons) and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang through nuclear reactions in a process called Big Bang nucleosynthesis. After about 20 minutes, the universe had expanded and cooled to a point at which these high-energy collisions a N… Stellar nucleosynthesis is the nuclear process by which new nuclei are produced. It occurs in stars during stellar evolution. It is responsible for the galactic abundances…

adopted as the standard: iron abundance in a galaxy increases roughly linearly with time through successive generations of stellar nucleosynthesis and supernova In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal currently detectable (i.e. non-dark) matter in the universe is either hydrogen or helium, and astronomers use the word metals as convenient shorthand for all elements except hydrogen and helium. This word-use is distinct from the conventional chemical or physica In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal currently detectable (i.e. non-dark) matter in the universe is either hydrogen or helium, and astronomers use the word metals as convenient shorthand for all elements except hydrogen and helium. This word-use is distinct from the conventional chemical or physical definition of a metal as an electrically conducting element. Stars and nebulae with relatively high abundances of heavier elements are called metal-rich in discussions of metallicity, even though many of those elements are called nonmetals in chemistry. The presence of heavier elements is the result of stellar nucleosynthesis. The majority of elements that are heavier than hydrogen and helium in the Universe are formed in the cores of stars as they evolve. Over time, stellar winds and supernovae deposit those heavier metals into the surrounding environment, which enriches the interstellar medium and provides material for the birth of new stars. Older generations of stars formed in a metal-poor early stage of the Universe, so it follows that they have lower metallicities than younger generations of stars which formed in a more metal-rich Universe. The metallicity of a star is most often expressed in terms of [Fe/H], which represents the logarithmic ration of iron to hydrogen relative to the Sun's value. There are several compounding reasons for why this scale has become adopted as the standard: iron abundance in a galaxy increases roughly linearly with time through successive generations of stellar nucleosynthesis and supernova enrichment, iron has a rich spectrum that creates hundreds of absorption lines across the optical range, making iron lines extremely prominent when mapping the solar spectrum, and finally, iron was recognized as the default reference element in the mid-20th century due to how reliably it could be measured, today's standards are built on a history of iron-centric calibrations.