Hipparcos Intermediate Astrometric Data ( IAD ) have been used to derive astrometric orbital elements for spectroscopic binaries from the newly released Ninth Catalogue of Spectroscopic Binary Orbits ( S _ { B ^ { 9 } } ) .
This endeavour is justified by the fact that ( i ) the astrometric orbital motion is often difficult to detect without the prior knowledge of the spectroscopic orbital elements , and ( ii ) such knowledge was not available at the time of the construction of the Hipparcos Catalogue for the spectroscopic binaries which were recently added to the S _ { B ^ { 9 } } catalogue .

Among the 1374 binaries from S _ { B ^ { 9 } } which have an HIP entry ( excluding binaries with visual companions , or DMSA/C in the Double and Multiple Stars Annex ) , 282 have detectable orbital astrometric motion ( at the 5 % significance level ) .
Among those , only 70 have astrometric orbital elements that are reliably determined ( according to specific statistical tests ) , and for the first time for 20 systems .
This represents a 8.5 % increase of the number of astrometric systems with known orbital elements ( The Double and Multiple Systems Annex contains 235 of those DMSA/O systems ) .

The detection of the astrometric orbital motion when the Hipparcos IAD are supplemented by the spectroscopic orbital elements is close to 100 % for binaries with only one visible component , provided that the period is in the 50 - 1000 d range and the parallax is > 5 mas .
This result is an interesting testbed to guide the choice of algorithms and statistical tests to be used in the search for astrometric binaries during the forthcoming ESA Gaia mission .

Finally , orbital inclinations provided by the present analysis have been used to derive several astrophysical quantities .
For instance , 29 among the 70 systems with reliable astrometric orbital elements involve main sequence stars for which the companion mass could be derived .
Some interesting conclusions may be drawn from this new set of stellar masses , like the enigmatic nature of the companion to the Hyades F dwarf HIP 20935 .
This system has a mass ratio of 0.98 but the companion remains elusive .