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in march 2002 we started a campaign to obtain orbital solutions of 100 subdwarf b ( sdb ) binaries from the edinburgh - cape ( ec ) survey ( stobie et al .
this work was intended as the southern hemisphere counterpart of that undertaken by maxted et al .
( 2001 ) and morales - rueda et al .
( 2003 ) . in their work morales - rueda
( 2003 ) select their targets from two main sources , the palomar - green ( pg ) and the kitt peak - downes ( kpd ) catalogues .
the pg catalogue is biased against targets that show a ca ii h - line ( as these were taken out of the catalogue ) , and thus , against sdb binaries with main sequence companions . on the other hand
the ec survey does not show these biases , as the object selection is based on colours only , and is ideal to obtain an `` unbiased '' sample of sdb binaries that can then be compared with binary evolution theories ( han et al .
we should mention that some bias might still remain as in the cases where the main sequence star was somewhat brighter than the sdb star ( i.e. combined colour redder than @xmath0 = @xmath10.4 ) , the binary would have been classified probably as a late a star and would have been taken out of the catalogue .
the spectra were obtained with the grating spectrograph plus the site ccd at the 1.9 m radcliffe telescope at the saao .
grating 4 , with 1200 grooves per mm was used to obtain spectra covering h@xmath2 and h@xmath3 with a dispersion of 0.5 / pix and a resolution of less than 1  at 4600 .
the spectra were reduced according to standard procedures .
the balmer lines were fitted with a model line profile consisting of three gaussians to measure their radial velocities .
these were then fitted with functions consisting of a sinusoidal plus a constant with 4 free parameters , i.e. the constant , the semiamplitude of the sinusoidal , the period and the zero point .
a value of the @xmath4 of each fit was obtained for each combination of parameters and a periodogram of the form shown in the right hand panels of figs . 1 , 2 and 3 , obtained for each system .
we considered that the orbital period of the binary was determined when the difference in @xmath4 between the first and second alias was larger than 20 .
we calculated the probability that the true orbital period lies further than 1 and 10 per cent from our chosen period and present these values in table 1 together with the orbital solution for each system . for details on the data reduction ,
period determination and probability calculations see morales - rueda et al .
we find the orbital solutions for two systems ec00404@xmath14429 and ec02200@xmath12338 .
these are presented in table 1 and in figs . 1 and 2 respectively .
for another system , ec12327@xmath11338 , we find that the orbital period lies around 0.36 d but the number of observations is not enough to obtain an accurate orbital period .
lccc & ec00404@xmath14429 & ec02200@xmath12338 & ec12327@xmath11338 + period [ d ] & 0.12834(4 ) & 0.8022(7 ) & 0.3628 - 0.3674 + hjd@xmath5 [ d ] & 2452895.4418(4 ) & 2452896.029(4 ) & + @xmath3 [ km s@xmath6 & 32.97 @xmath7 2.94 & 20.74 @xmath7 2.29 & @xmath17.43 - @xmath14.06 + k [ km s@xmath6 & 152.8 @xmath7 3.4 & 96.35 @xmath7 1.43 & 119.8 - 124.3 + m@xmath8min [ m@xmath9 & 0.32 & 0.39 & 0.38@xmath10 + @xmath11 & 1.3 & 0.42 & 1.6 - 3.6 + 2nd best alias [ d ] & 0.11350(3 ) & 0.3038(1 ) + @xmath12 & 73 & 61 + n & 9 & 10 & 13 + 1 per cent & -15.18 & -11.35 & -3.47@xmath10 + 10 per cent & -15.18 & -11.35 & -10.81@xmath10 + systematic error & 2 & 2 & 2 +
their orbital periods place ec00404@xmath14429 , ec02200@xmath12338 and ec12327@xmath11338 in the group of sdb binaries formed via the common envelope ( ce ) ejection channel ( see fig . 10 of han et al . 2003 ) .
the minimum mass of the companion , calculated assuming the canonical mass of 0.5m@xmath13 for the sdb , indicates that the companions are probably white dwarfs , thus these binaries have probably formed through the second ce path ( han et al .
2003 ) .
we have added the orbital periods of these three new systems to the orbital period distribution of sdbs known , fig .
the most interesting features of this distribution are the excess of binaries at orbital periods around 1 d and that the very long period systems ( tens and hundreds of days ) are starting to appear in the sample . the comparison of the observed distribution with theoretical predictions ( han et al .
2003 ) is invaluable to determine , among other important evolutionary unknowns , plausible values for the ce ejection efficiency .
han , z. , podsiadlowski , ph . , maxted , p.f.l . , marsh , t.r .
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heber , u. 2003 , , 338 , 752 morales - rueda , l. , maxted , p.f.l . ,
marsh t.r .
2004 , proceedings of the workshop `` extreme horizontal branch stars and related objects '' , astrophysics and space science , kluver academic publishers , ed .
we present the first results of a campaign to obtain orbital solutions of subdwarf b ( sdb ) stars from the edinburgh - cape survey . 
 we have obtained blue spectra of 35 sdbs , 20 of which have been observed in more than two epochs . 
 15 out of the 35 are certain binaries with a few other objects showing radial velocity variations with small amplitude , possibly long period sdb binaries . 
 we have secured the orbital parameters for 2 of the 15 systems and narrowed down the orbits of another one to a small range of periods . 
 these preliminary results only use data taken up to december 2003 .