A&A 383, 558–567 (2002) Astronomy DOI: 10.1051/0004-6361:20011746 & c ESO 2002 Astrophysics The spectroscopic binaries 21 Her and γ Gem? H. Lehmann1, S. M. Andrievsky2,3, I. Egorova3,4, G. Hildebrandt5,S.A.Korotin3,4,K.P.Panov6, G. Scholz5, and D. Sch¨onberner5 1 Th¨uringer Landessternwarte Tautenburg, Karl-Schwarzschild-Observatorium, 07778 Tautenburg, Germany 2 Instituto Astronˆomico e Geof´ısico, Universidade de S˜ao Paulo, Av. Miguel Stefano, 4200, S˜ao Paulo SP, Brazil e-mail:
[email protected] 3 Department of Astronomy, Odessa State University, Shevchenko Park, 65014 Odessa, Ukraine e-mail:
[email protected] 4 Isaac Newton Institute of Chile, Odessa Branch, Ukraine 5 Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany e-mail:
[email protected],
[email protected],
[email protected] 6 Institute of Astronomy, Bulgarian Academy of Sciences, Sofia, Bulgaria e-mail:
[email protected] Received 21 May 2001 / Accepted 6 December 2001 Abstract. In the framework of a search campaign for short-term oscillations of early-type stars we analysed recently obtained spectroscopic and photometric observations of the early A-type spectroscopic binaries 21 Her and γ Gem. From the radial velocities of 21 Her we derived an improved orbital period and a distinctly smaller eccentricity in comparison with the values known up to now. Moreover, fairly convincing evidence exists for an increase of the orbital period with time. In addition to the orbital motion we find further periods in the orbital residuals. The longest period of 57d. 7 is most likely due to a third body which has the mass of a brown dwarf, whereas the period of 1d.