tokens: of Sgr in that area of the sky with mean velocities v r 130 and115kms 1 . The position of these peaks are compatible with the ones derived from the velocity distribution of the target stars. According to the classification provided by these models, the bulk of Sgr stars around v r 130kms 1 might belong to the trailing arm of that halo substructure while the less significant peak might correspond to the leading arm. The mean heliocentric distance predicted by PR10 for both wraps in this area of the sky is d 30kpc. On the other hand, LM10 predicts mean distances of d 21 and 28kpc for the leading and trailing arms, respectively. The expected two sections of the Sgr tidal stream along the line of sight to Whiting1 are evident in our spectroscopic results but not in the colourmagnitude diagram (CMD) shown in Fig. 1 . We analyse the distribution of target stars belonging to the Sgr components as a function of g by counting stars associated with the leading [160 v r (kms 1 )100] and trailing [90 v r (kms 1 )150] arms with a bin size of g 0.1. Fig. 3 shows the normalized distribution obtained for both populations and we are not able to determine a shift in the g band between the subsamples of target stars. This might indicate that the leading and trailing arms of Sgr are spatially coincident or have slightly different distances, making it difficult to distinguish the populations in the CMD. Therefore, our results are in good agreement with the predictions made by the PR10 model both for the position and the kinematics of the leading and trailing components of the Sgr tidal stream around Whiting1. Figure 3. Left-hand panel: CMD for stars beyond 10arcmin from the centre of Whiting1. The positions in the diagram of stars belonging to the Sgr trailing and leading wraps are indicated as orange stars and green triangles, respectively. The blue isochrone corresponds to a t 10Gyr and [Fe/H] 1.5 population. Right-hand panel: normalized distribution of stars belonging to both arms as a function of g in the range 19 g 23.5 and following the same colour code as in the left-hand panel. According to the PR10 classification, target stars with radial velocities around v r 120kms 1 might be associated with an old component of the leading arm of Sagittarius, accreted a long time ago (2Gyr). While the northern and southern trailing arms have been well characterized using different tracers such as RRLyrae, blue horizontal branch, sub-giant branch and red clump stars (e.g. Koposov etal. 2012 ; Belokurov etal. 2014 ), the southern leading arm predicted both by PR10 and LM10 , has remained undetected. This might be due to the coincidence of its projected path with that of the trailing arm or to its lower surface brightness. Only tentative detections have been reported using alternative tracers such as carbon stars, with distances and velocities consistent with our results along that line of sight (Huxor Grebel 2015 ). Alternatively, the group of stars with positive radial
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