S20B0080abst
S20B0080
The Helmi stream is a candidate of an accretion signature that was discovered from stellar kinematics about 20 years ago. There has been no evidence of its distinctness in the space of chemical abundance, which hampers a clear identification of its progenitor. The recent Gaia data release, however, provides a dramatically larger list of its member stars, providing new implications about its chemical distinctness and opening a window to study its abundance precisely. We, therefore, propose to revisit the chemical abundance of the Helmi stream with much higher precision than previous studies. The updated member list contains two mildly Zinc-enhanced stars, which suggests chemical distinctness of the Helmi stream for the first time. However, it is not yet clear if the Zinc-enhancements are ubiquitous among the stream member stars since their abundances have not been measured precisely enough except for the two Zinc-rich stars. The updated list from the Gaia data now contains a large number of member stars suitable for the precise abundance measurements, enabling the confirmation of the Zinc-enhancements. Combining with our previous program for other accretion signatures, this proposal will enable to understand the Helmi stream in the context of the Milky Way merging history.
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