  In anticipation of the Gaia astrometric mission, a large sample of
spectroscopic binaries is being observed since 2010 with the Sophie
spectrograph at the Haute--Provence Observatory. Our aim is to derive the
orbital elements of double-lined spectroscopic binaries (SB2s) with an accuracy
sufficient to finally obtain the masses of the components with relative errors
as small as 1% when the astrometric measurements of Gaia are taken into
account. Simultaneously, the luminosities of the components in the Gaia
photometric band G will also be obtained. Our observation program started with
200 SBs, including 152 systems that were only known as single-lined. Thanks to
the high efficiency of the Sophie spectrograph, an additional component was
found for 25 SBs. After rejection of 5 multiple systems, 20 new SB2s were
retained, including 8 binaries with evolved primary, and their mass ratios were
derived. Our final sample contains 68 SB2s, including 2 late-type giants and 10
other evolved stars.
