Kavli Affiliate: Anna Frebel
| First 5 Authors: Mohammad K. Mardini, Anna Frebel, Anirudh Chiti, ,
| Summary:
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 $>
10^{52}$,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
$sim10^{-5}$,M$_{odot}$ 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.
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