**Table 1:** Some basic parameters of the studied objects taken from the General Catalogue of Variable Stars (Kholopov et al. 1998). The distances come from the HIPPARCOS catalogue (Perryman et al. 1997).
Star	Spectral	Variability	Period	Distance
	type	type	(days)	(pc)
$\alpha$ Ori	M 1I	SRc	2335	131
SW Vir	M 7III	SRb	150	143
R Leo	M 8IIIe	Mira	310	101

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