  Evolved stars with a helium core can be formed by non-conservative mass
exchange interaction with a companion or by strong mass loss. Their masses are
smaller than 0.5 MSun. In the database of the Sloan Digital Sky Survey (SDSS),
there are several thousand stars which were classified by the pipeline as dwarf
O, B and A stars. Considering the lifetimes of these classes on the main
sequence, and their distance modulus at the SDSS bright saturation, if these
were common main sequence stars, there would be a considerable population of
young stars very far from the galactic disk. Their spectra are dominated by
Balmer lines which suggest effective temperatures around 8000-10000K. Several
thousand have significant proper motions, indicative of distances smaller than
1kpc. Many show surface gravity in intermediate values between main sequence
and white dwarf, 4.75 < log g < 6.5, hence they have been called sdA stars.
Their physical nature and evolutionary history remains a puzzle. We propose
they are not H-core main sequence stars, but helium core stars and the outcomes
of binary evolution. We report the discovery of two new extremely-low mass
white dwarfs among the sdAs to support this statement.
