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tokens: part of the H α line is not due to chromospheric activity. Figure 11. Variations in the Mg ii λ2800 emission line in several IUE spectra. [A colour version of this figure is available in the online version.] Following the procedure explained in Acker Jasniewicz ( 1990 ) for Abell 35, we have tried to find a modulation of the H α profile with the rotation phase, by measuring the flux variation between the nearby continuum and the deepest point of the H α absorption core. In contrast to the results found by Acker Jasniewicz ( 1990 ) in the case of Abell 35, we do not find any correlation with the rotational period during the long time span of the observations in LoTr 5. We have inspected the H α profile in all the Hermes spectra and we found no correlation with the rotation period, see Fig. A1 , where we show the phased-folded trailed spectra of the H α line with the rotation period. The Ca ii HK λλ3933, 3967 lines appear in emission in the HERMES data set (as already reported by Strassmeier et al. 1997 ). We do not find variations in these lines at the level of the H α variations that we find in HERMES data. Hence, Ca ii HK lines are not useful for studying the activity of the star. 3.5.2 Accretion disc around the possible close companion The presence of an accretion disc in LoTr 5 has been also discussed in the literature. If indeed the H α emission was due to an accretion disc, then the double-peaked profile would come from two different emission regions instead of a broad emission feature. Montez et al. ( 2010 ) already discussed the system within this scenario: since the presence of an accretion disc would imply the RLOF, they calculated the Roche lobe radius ( R L ) assuming the synchronization of the rotation and orbital period (i.e. they assumed a close 0.6 M ⊙ companion at ∼5.9 d). Under this configuration, the R L was below the radius of the star, filling its Roche Lobe and allowing the existence of an accretion disc. However, from our radial velocity analysis, we know that it is not possible to have such a massive companion so close to the G-type star. On the contrary, in the case we would have a low-mass object at ∼5.9 d, the R L would be ∼16 R⊙, and the star could not have filled its Roche lobe. Therefore, with the current data, we conclude that it is not possible to have an accretion disc via RLOF in LoTr 5. Finally, and as mentioned in Section 3.2 , no significant infrared excess is identified in the SED, which would point out that an accretion disc is highly unlikely in the system. 3.5.3 The possible resemblance with symbiotic stars Finally, it is worth mentioning that this double-peaked H α emission resembles the observed in some symbiotic stars (SS), the widest interacting binary systems known with a white dwarf accreting material from a giant star via stellar winds (see e.g. Van Winckel, Duerbeck Schwarz 1993 ; Burmeister Leedjärv 2009 ). These systems are sometimes embedded into a bipolar nebula similar to some PNe (like