The R-Process Alliance: Discovery of an Extremely R-process-enhanced Thin-disk Star

Highly r-process-enhanced stars are rare and usually metal-poor

([Fe/H] < -1.0), and mainly populate the Milky Way halo

and dwarf galaxies. This study presents the discovery of a relatively

bright (V = 12.72), highly r-process-enhanced (r-II) star ([Eu/Fe]

= +1.32, [Ba/Eu] = -0.95), LAMOST J020632.1+494127.9. This

star was selected from the Large Sky Area Multi-Object Fiber

Spectroscopic Telescope (LAMOST) medium-resolution (R ~ 7500)

spectroscopic survey; follow-up high-resolution (R ~ 25,000)

observations were conducted with the High Optical Resolution

Spectrograph (HORuS) installed on the Gran Telescopio Canarias.

This star has a high metallicity ([Fe/H] = -0.54) compared to most other highly r-process-enhanced

stars, and has the highest measured abundance ratio of Eu to H ([Eu/H]

= +0.78). It is classified as a thin-disk star based on its

kinematics, and does not appear to belong to any known stream or dwarf

galaxy. I also report on several additional RPE disk candidates

which have recently been observed at high resolution, and age limits on

them obtained from the [Th/Eu] chronometer.