The abundances of heavy elements in BL138 – red giant of local group fornax dwarf spheroidal galaxy

Abstract

Using the spectrum obtained with FLAMES/GIRAFFE multi-object spectrograph installed at ESO Very
Large Telescope we investigated the absorption lines of heavy elements in the spectrum of BL138. This
red giant star belongs to one of the Local Group members – Fornax dwarf spheroidal galaxy. The
abundances of 12 stable chemical elements, namely Y, Zr, Nb, Mo, Ru, La, Ce, Pr, Nd, Eu, Dy, Er, Lu,
and Hf. The abundance of radioactive elements Ac and Th are also investigated. The analysis of these
abundances and also previously published investigation of BL138 allowed claiming that the distribution
of abundances is different from that in the solar photosphere. The signs of r-process in the abundance
pattern of BL138 are not important. The production of elements from barium to hafnium can be explained
by s-process. The abundances of elements from yttrium to ruthenium are lower than it can be expected in
the case of s-process synthesis. That is why it can be expected that several nuclear processes took place in
the synthesis of these elements. The possibility of detection the actinium absorption line in the spectrum
of BL138 clearly indicate the possibility of physical process which results in continuous production of
actinium in the atmosphere of BL138. The actinium abundance can be close to logN(Ac)=1.9. It can be
the result of hydrogen accretion from interstellar medium on stellar photosphere. The trends of
abundances with second ionization potentials of corresponding chemical elements, and also by the
emissions in the profiles of hydrogen H α line confirm this identification.