**Table 1:** Main parameters of observed active stars.
Parameter	HK Lac	IM Peg	VY Ari
HD	209813	216489	17433
Sp. type	K0III	K2III-II	K3-4V-IV
$v\sin i$ (km s^-1)	23.0^a	25.6^b	8.6^c
$P_{\rm rot}$ (days)	24.4284^d	24.4936^e	16.1996^e
$T_{\rm max}$ (K)	4765^f	4666^f	4916^f
$V_{\rm max}$ (mag)	6.66^h	5.55ⁱ	6.69^l
$V_{\rm ph}$ (mag)	6.73^f	5.72^f	6.84^f
Ephemerids
HJD0	2 440 017.17^g	2 443 734.0^e	2 451 856.0^f
$P_{\rm phot}$ (days)	24.283^f	24.789^f	16.292^f

^a Randich et al. (1994).
^b De Medeiros & Mayor (1999).
^c Bopp et al. (1989).
^d Orbital period (Gorza & Heard 1971).
^e Strassmeier et al. (1997).
^f Present work.
^g Strassmeier et al. (CABS 1993).
^h Oláh et al. (1997).
ⁱ Berdyugina et al. (1999).
^l Strassmeier & Bopp (1992).

Source LaTeX | All tables | In the text

	1 Introduction
	2 Targets selection and observations
	3 Data analysis
	4 The spot model
	5 Results
	6 Discussion
	7 Conclusion
	References
	Online Material
	Appendix A: The hemisphere-averaged temperature and luminosity