Table 6: Heliocentric radial velocities for the sdB- and the cool star components of TON 139 and PG 1718+519.
star date HJD-2450000 exposure S/N $v_{\rm rad}$ [kms^-1] $v_{\rm rad}$ [kms^-1]

UT time [s] (sdB component) (cool companion)

TON 139 1996-01-14 96.91396 600 95.6 -6.3 $\pm$ 4.9 19.9 $\pm$ 0.6

TON 139 1996-03-11 153.84515 300 71.9 -7.4 $\pm$ 7.8 20.2 $\pm$ 0.7

TON 139 1996-06-09 243.75586 600 66.5 -13.1 $\pm$ 8.4 21.8 $\pm$ 0.8

TON 139 1997-01-28 476.96939 1800 69.4 -20.2 $\pm$ 7.9 20.2 $\pm$ 0.9

TON 139 1997-07-04 633.66734 500 72.7 32.6 $\pm$ 6.7 22.4 $\pm$ 0.7

TON 139 1998-01-22 836.03834 750 82.9 -22.1 $\pm$ 9.1 20.7 $\pm$ 0.6

TON 139 mean -3.6 $\pm$ 20.2 20.8 $\pm$ 1.0

PG1718+519 1997-09-10 701.71120 1400.0 82.0 -69.2 $\pm$ 10.1 -68.0 $\pm$ 0.9

**Table 6:** Heliocentric radial velocities for the sdB- and the cool star components of TON 139 and PG 1718+519.
star	date	HJD-2450000	exposure	S/N	$v_{\rm rad}$ [kms^-1]	$v_{\rm rad}$ [kms^-1]
	UT		time [s]		(sdB component)	(cool companion)
TON 139	1996-01-14	96.91396	600	95.6	-6.3 $\pm$ 4.9	19.9 $\pm$ 0.6
TON 139	1996-03-11	153.84515	300	71.9	-7.4 $\pm$ 7.8	20.2 $\pm$ 0.7
TON 139	1996-06-09	243.75586	600	66.5	-13.1 $\pm$ 8.4	21.8 $\pm$ 0.8
TON 139	1997-01-28	476.96939	1800	69.4	-20.2 $\pm$ 7.9	20.2 $\pm$ 0.9
TON 139	1997-07-04	633.66734	500	72.7	32.6 $\pm$ 6.7	22.4 $\pm$ 0.7
TON 139	1998-01-22	836.03834	750	82.9	-22.1 $\pm$ 9.1	20.7 $\pm$ 0.6
TON 139	mean				-3.6 $\pm$ 20.2	20.8 $\pm$ 1.0
PG1718+519	1997-09-10	701.71120	1400.0	82.0	-69.2 $\pm$ 10.1	-68.0 $\pm$ 0.9

Important additional information can be obtained from radial velocity measurements. A systematic search for radial velocity variations of our programme stars is needed. Such projects have already been started by Saffer et al. (2001) and Maxted et al. (2001) who observed six of our programme stars (PB 6107, PHL 1079, PG 0749+658, TON 1281, PG 1449+653 and PG 2148+095). None of them showed significant radial velocity changes.

Saffer et al. (2001) find in their survey of 21 composite spectrum sdB stars that the velocity variations of the individual components as well as the velocity difference between the two components are very small (less than a few kms^-1) or undetectable, and conclude that the binaries have likely periods of many months to several years. Green et al. (2001) estimate from these measurements that the current periods average 3-4 years with separations 540-650 $R_{\odot}$ .

We have obtained multiple precise radial velocities for TON 139 and a single measurement of PG 1718+519 using the MMT Blue Channel spectrograph at 1 Å resolution from 4000-4930 Å (see Table 6). The radial velocities of the cool companions were determined by cross correlation against super-templates of main sequence spectral types from F6 to K5. The sdB velocities were derived using a preliminary attempt at subtracting out the cool star companion spectrum. For details of the data reduction and analysis see Saffer et al. (2001). Improved sdB velocities using better cool star template spectra for the subtractions will be determined by Green et al. (2002, in prep.).

For TON 139 the cool star's velocity is constant, whereas the sdB velocity is changing by more than 50kms^-1. This can be explained if an additional companion is orbiting the sdB star. This companion has to be so faint that it does not contribute to the light in the R band. Hence we have to conclude that the resolved system TON 139 is a triple system. A radial velocity study of PG 1718+519, the second resolved system in our sample, is not available yet. The single measurement listed in Table 6 gives identical radial velocities for the sdB and the cool companion. This argues against a third faint component orbiting the sdB star in a narrow orbit as was found for TON 139. Additional radial velocity measurements are urgently needed to clarify the nature of PG 1718+519. Assuming that PG 1718+519 is not triple, this would be the only resolved binary system in our sample of 19 objects.

6 Radial velocities