We report on the discovery of the first ultra metal-poor (UMP) star 2MASS~J20500194−6613298 (J2050−6613; \mbox{[Fe/H] = −4.05}) selected from the Gaia BP/RP spectral catalog that belongs to the ancient Atari disk 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 \textbf{(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.
@article{arxiv.2402.07046,
title = {A Strontium-rich Ultra Metal-poor Star in the Atari Disk Component},
author = {Mohammad K. Mardini and Anna Frebel and Anirudh Chiti},
journal= {arXiv preprint arXiv:2402.07046},
year = {2024}
}