Study of the distribution of the heaviest elements in the galactic halo

Abstract

We study the concentration of an r-process element such as europium in the north galactic halo, by examining the optical spectra of a sample of about 500 K1 stars distributed among 30 different plates from the SEGUE-2 at high galactic latitude. We have developed an automated method that ranks the stars by their likelihood of having an enhanced abundance of this element and identifies the plates that contain one or more of the stars which fall in the upper decile. For the present investigation, we specifically focus on the 4129.70 Å and 4205.05 Å absorption lines of Eu, finding several plates that contain a relatively high fraction of stars (> 5%) with show significant absorption around both wavelengths. The most promising plate is SEGUE-2’s number 3166, where we have measured fractions of stars potentially rich in Eu of 12% from each of the two lines, which are also the largest values reached in the present work