Photographic LTV (B_pg) of HD 179821 between 1899 and 1989 (Arkhipova et al. 2001). We note the deep minima between JD 24 24000 and JD 24 38000 (∼1925 and ∼1960) indicating a very red and cool episode, favourable for an eruption; see text. HR 8752 showed the same type of photometric history before its blue loop evolution, in which an eruptive episode occurred (1973) according to spectroscopic observations (Figs. 6 and 7).