Draco 119: A Remarkable Heavy Element-deficient Giant

Abstract

We report the abundance analysis of new high S/N spectra of the most metal-poor ([Fe/H] $= -2.95$) star presently known to be a member of a dwarf galaxy, the Draco dSph red giant, D119. No absorption lines for elements heavier than Ni are detected in two Keck HIRES spectra covering the $λλ$ 3850--6655 Å wavelength range, phenomenon not previously noted in any other metal-poor star. We present upper limits for several heavy element abundances. The most stringent limits, based on the non-detection of \ion{Sr}{2} and \ion{Ba}{2} lines, indicate that the total s- and r-process enrichment of D119 is at least 100 times smaller than Galactic stars of similar metallicity. The light element abundances are consistent with the star having formed out of material enciched primarily by massive Type II supernovae (M $> 20$--25 M$_{\odot}$). If this is the case, we are forced to conclude that massive, metal-poor Type II supernovae did not contribute to the r-process in the proto-Draco environment. We compare the abundance pattern observed in D119 to current predictions of prompt enrichement and pair-instability supernovae and find that the model predictions fail by an order or maginitude or more for many elements.