A strontium-rich ultra-metal-poor star in the Atari disc component

Abstract

We report on the discovery of the first ultra-metal-poor (UMP) star 2MASS J20500194-6613298 (J2050-6613; [Fe/H] = -4.05) selected from the Gaia BP/RP spectral catalogue that belongs to the ancient Atari disc component. We obtained a high-resolution spectrum for the star with the MIKE spectrograph on the Magellan-Clay telescope. J2050-6613 displays a typical chemical abundance pattern for UMP stars, including carbon and zinc enhancements. In contrast, J2050-6613 shows extremely high [Sr/Fe] and [Sr/Ba] ratios compared to other stars in the [Fe/H] < -4.0 regime. J2050-6613 is most likely an early Population II star that formed from a gas cloud that was chemically enriched by a massive Population III hypernova (E > 10⁵² erg). Such a Population III core-collapse hypernova could simultaneously explain the origin of the abundance pattern of light and heavy elements of 2MASS J2050-6613 if a large amount of Sr of ~10^-5 M_⊙ was produced, possibly by neutrino-driven (wind) ejecta. Therefore, the abundance pattern of 2MASS J2050-6613 places important constraints on Sr-producing nucleosynthesis sources operating in the Atari progenitor at the earliest times.