With the availability of parallaxes provided by the Tycho-Gaia Astrometric Solution , it is possible to construct the Hertzsprung-Russell diagram ( HRD ) of barium and related stars with unprecedented accuracy .
A direct result from the derived HRD is that subgiant CH stars occupy the same region as barium dwarfs , contrary to what their designations imply .
By comparing the position of barium stars in the HRD with STAREVOL evolutionary tracks , it is possible to evaluate their masses , provided the metallicity is known .
We used an average metallicity [ Fe/H ] = - 0.25 and derived the mass distribution of barium giants .
The distribution peaks around 2.5 M _ { \odot } with a tail at higher masses up to 4.5 M _ { \odot } .
This peak is also seen in the mass distribution of a sample of normal K and M giants used for comparison and is associated with stars located in the red clump .
When we compare these mass distributions , we see a deficit of low-mass ( 1 – 2 M _ { \odot } ) barium giants .
This is probably because low-mass stars reach large radii at the tip of the red giant branch , which may have resulted in an early binary interaction .
Among barium giants , the high-mass tail is however dominated by stars with barium indices of less than unity , based on a visual inspection of the barium spectral line ; that is , these stars have a very moderate barium line strength .
We believe that these stars are not genuine barium giants , but rather bright giants , or supergiants , where the barium lines are strengthened because of a positive luminosity effect .
Moreover , contrary to previous claims , we do not see differences between the mass distributions of mild and strong barium giants .