Abundances for 27 elements in the very metal poor dwarf star HE 2148–1247 are presented , including many of the neutron capture elements .
We establish that HE 2148–1247 is a very highly s-process enhanced star with anomalously high Eu as well , Eu/H \sim half Solar , demonstrating the large addition of heavy nuclei at [ Fe/H ] = -2.3 dex .
Ba and La are enhanced by a somewhat larger factor and reach the solar abundance , while Pb significantly exceeds it , thus demonstrating the addition of substantial s -process material .
Ba/Eu is ten times the solar r -process ratio but much less than that of the s -process , indicating a substantial r -process addition as well .
C and N are also very highly enhanced .
We have found that HE 2148–1247 is a radial velocity variable ; it is probably a small amplitude long period binary .
The C , N and the s -process element enhancements thus presumably were produced through mass transfer from a former AGB binary companion .
The large enhancement of heavy r -nuclides also requires an additional source as this is far above any inventory in the ISM at such low [ Fe/H ] .
We consider that the s -process material was added by mass transfer of a more massive companion during its thermally pulsating AGB phase and ending up as a white dwarf .
We further hypothesize that accretion onto the white dwarf from the envelope of the star caused accretion induced collapse of the white dwarf , forming a neutron star , which then produced heavy r -nuclides and again contaminated its companion .
This mechanism in a binary system can thus enhance the envelope of the lower mass star in s and r -process material sequentially .
Through analysis of the neutron capture element abundances taken from the literature for a large sample of very metal poor stars , we demonstrate , as exemplified by HE 2148–1247 , that mass transfer in a suitable binary can be very efficient in enhancing the heavy elements in a star ; it appears to be capable of enhancing the s -process elements in very metal poor stars to near the solar abundance , but not substantially above it .
The yield of Pb relative to Ba appears to vary among very metal poor stars .