3 Historical photometric observations

All the program stars listed in Table 2 were already known to be variable at optical wavelengths. They were selected for the present monitoring program on the basis of their rotation period within the range 0.4-1.1 days and with the aim of confirming the previously determined rotation periods and determining for each star the maximum light curve amplitude in the quoted rotation range. In this section a brief summary of the previous estimates of rotation period and light curve amplitudes is given:

HII 250: Marilli et al. (1997) discovered its optical variability obtaining a light curve amplitude of $\Delta V=0.06$ mag and a period of $P=0.84^{\rm d}$. This is the only star whose photometric period from the present monitoring program is quite different than previously determined.

HII 324 (=V632 Tau): Haro & Chavira (1973) discovered that it is a flare star. The first optical band light curves were obtained by Stauffer et al. (1987) with an amplitude of $\Delta V=0.18$ mag and $\Delta V=0.20$ mag in two different epochs.

HII 335 (=MX Tau): Haro & Chavira (1973) discovered that it is a flare star. The first optical band light curve was obtained by Stauffer et al. (1987) with a photometric period of $P=0.36^{\rm d}$ and an amplitude of $\Delta V=0.09$ mag.

HII 345: Marilli et al. (1997) discovered its optical variability with a photometric period of $P=0.682^{\rm d}$ and an amplitude of $\Delta V=0.065$ mag. Further photometry was collected by Krishnamurthi et al. (1998) who reported an amplitude of $\Delta V=0.05$ mag and a longer period of $P=0.81^{\rm d}$.

HII 625 (=V811 Tau): Meys et al. (1982) discovered that it is variable in the V-band with a period of $P=0.43^{\rm d}$ and an amplitude of $\Delta V=0.13$ mag. Stauffer et al. (1987) found the same period and an amplitude of $\Delta V=0.18$ mag.

HII 686 (=OU Tau): Haro & Chavira (1973) discovered that it is a flare star. The first optical band light curve was obtained by Van Leeuwen et al. (1987) with a period of $P=0.396^{\rm d}$ and amplitude of $\Delta V=0.18$ mag. Stout-Batalha & Vogt (1999) have recently confirmed the rotation period, reporting a light curve amplitude of $\Delta V=0.11$ mag and $\Delta V=0.23$ mag during their observations.

HII 738 (=V1041 Tau): Marilli et al. (1997) discovered its optical band variability with an amplitude of $\Delta V=0.085$ mag and a period of $P=1.46^{\rm d}$. Krishnamurthi et al. (1998) collected further photometry reporting an amplitude of $\Delta V=0.09$ mag and a much shorter period of $P=0.73^{\rm d}$ in agreement with that found in the present monitoring.

HII 739 (=V696 Tau): the optical band variability was discovered by Marilli et al. (1997) with an amplitude of $\Delta V=0.05$ mag and a period of $P=0.90^{\rm d}$.

HII 882: the optical band variability was discovered by Meys et al. (1982) with an amplitude of $\Delta V=0.12$ mag and a period of $P=0.579^{\rm d}$. Marilli et al. (1997) determined a period of $P=0.604^{\rm d}$ and an amplitude of $\Delta V=0.10$ mag.

HII 1039: Pigatto & Rosino (1973) discovered that it is a flare star. The optical band variability was discovered by Meys et al. (1982) with an amplitude of $\Delta V=0.03$ mag and an uncertain period of $P=0.85^{\rm d}$. This is slightly longer than the period obtained in the present study.

HII 1532: Ambartsumian et al. (1972) discovered that it is a flare star. The first optical band light curve was obtained by Krishnamurthi et al. (1998) reporting an amplitude of $\Delta V=0.06$ mag and a photometric period of $P=0.78^{\rm d}$. This is shorter than the period derived in the present study.

HII 1653 (=V338 Tau): Haro & Chavira (1965) discovered that it is a flare star. The first optical band light curve was obtained by Krishnamurthi et al. (1998) reporting an amplitude of $\Delta V=0.10$ mag and a photometric period of $P=0.74^{\rm d}$.

HII 2244 (=V664 Tau): Haro & Chavira (1973) discovered that it is a flare star. The first optical band light curve was obtained by Stauffer et al. (1987) with an amplitude of $\Delta V=0.17$ mag and with a photometric period of $P=0.565^{\rm d}$.

HII 3063 (=V667 Tau): Haro & Chavira (1973) discovered that it is a flare star. The first optical band light curve was obtained by Prosser et al. (1995) with an amplitude of $\Delta V=0.10$ mag and a photometric period of $P=0.89^{\rm d}$.

Figure 1: $A_{\max}$ versus rotation period (P). Asterisks and bullets indicate the newly presented light curve amplitudes of the Pleiades and Alpha Persei members, respectively; diamonds indicate the amplitude values taken from Messina et al. (2001). Solid line is the fit to the data upper envelope from Messina et al. (2001)

Figure 2: As Fig. 1, but for G8-K4 type stars

Figure 3: As Fig. 1, but for K5-M4 type stars

Figure 4: HII 250 V-band light curve and colors collected over the interval 10-13 Oct. and 8-10 Nov. 1999. Phases are reckoned from the photometric ephemeris 2451457.4167 + 0.591$\cdot$E

Figure 5: HII 324 (=V632 Tau) V-band light curve and colors collected over the interval 9-13 Oct. and 9-10 Nov. 1999. Phases are reckoned from the photometric ephemeris 2451457.4167 + 0.411$\cdot$E

Figure 6: HII 335 (=MX Tau) V-band light curve and colors collected over the interval 5-13 Oct. and 10 Nov. 1999. Phases are reckoned from the photometric ephemeris 2451457.4167 + 0.4073$\cdot$E

Figure 7: HII 345 V-band light curve and colors collected over the interval 6-13 Oct. and 8-10 Nov. 1999. Phases are reckoned from the photometric ephemeris 2451457.4167 + 0.723$\cdot$E

Figure 8: HII 625 (=V811 Tau) V-band light curve and colors collected over the interval 5-13 Oct. and 8-10 Nov. 1999. Phases are reckoned from the photometric ephemeris 2451457.4167 + 0.421$\cdot$E

Figure 9: HII 686 (=OU Tau) V-band light curve and colors collected over the interval 6-13 Oct. and 8-10 Nov. 1999. Phases are reckoned from the photometric ephemeris 2451457.4167 + 0.391$\cdot$E

Figure 10: HII 738 (=V1041 Tau) V-band light curve and colors collected over the interval 6-13 Oct. and 8-9 Nov. 1999. Phases are reckoned from the photometric ephemeris 2451457.4167 + 0.854$\cdot$E

Figure 11: HII 739 (=V696 Tau) V-band light curve and colors collected over the interval 6-13 Oct. and 8-10 Nov. 1999. Phases are reckoned from the photometric ephemeris 2451457.4167 + 0.917$\cdot$E

Figure 12: HII 882 V-band light curve and colors collected over the interval 5-11 Oct. and 8-10 Nov. 1999. Phases are reckoned from the photometric ephemeris 2451457.4167 + 0.581$\cdot$E

Figure 13: HII 1039 V-band light curve and colors collected over the interval 6-13 Oct. and 8-10 Nov. 1999. Phases are reckoned from the photometric ephemeris 2451457.4167 + 0.784$\cdot$E

Figure 14: HII 1532 V-band light curve and colors collected over the interval 5-13 Oct. and 8-10 Nov. 1999. Phases are reckoned from the photometric ephemeris 2451457.4167 + 0.918$\cdot$E

Figure 15: HII 1653 (=V338 Tau) V-band light curve and colors collected over the interval 11-13 Oct. and 8-10 Nov. 1999. Phases are reckoned from the photometric ephemeris 2451457.4167 + 0.759$\cdot$E

Figure 16: HII 2244 (=V664 Tau) V-band light curve and colors collected over the interval 10-13 Oct. and 8 Nov. 1999. Phases are reckoned from the photometric ephemeris 2451457.4167 + 0.562$\cdot$E

Figure 17: HII 3063 (=V667 Tau) V-band light curve and colors collected over the interval 6-13 Oct. and 8-9 Nov. 1999. Phases are reckoned from the photometric ephemeris 2451457.4167 + 0.884$\cdot$E

Figure 18: AP 15 V-band light curve and colors collected over the interval 2-4 Dec. 1999. Phases are reckoned from the photometric ephemeris 2451515.0 + 0.622$\cdot$E

Figure 19: AP 19 (=V531 Per, HE622) V-band light curve and colors collected over the interval 2-4 Dec. 1999. Phases are reckoned from the photometric ephemeris 2451515.0 + 0.77$\cdot$E

Figure 20: AP 32 (HE684) V-band light curve and colors collected over the interval 2-4 Dec. 1999. Phases are reckoned from the photometric ephemeris 2451515.0 + 0.70$\cdot$E

Figure 21: AP 43 V-band light curve and colors collected over the interval 2-4 Dec. 1999. Phases are reckoned from the photometric ephemeris 2451515.0 + 0.582$\cdot$E

Figure 22: AP 93 V-band light curve and colors collected over the interval 2-3 Dec. 1999. Phases are reckoned from the photometric ephemeris 2451515.0 + 0.63$\cdot$E

Figure 23: AP 193 V-band light curve and colors collected over the interval 2-3 Dec. 1999. Phases are reckoned from the photometric ephemeris 2451515.0 + 0.645$\cdot$E

Figure 24: AP 244 V-band light curve and colors collected over the interval 2-4 Dec. 1999. Phases are reckoned from the photometric ephemeris 2451515.0 + 0.463$\cdot$E

AP 15: Stauffer et al. (1985) discovered its optical band variability with a period of $P=0.64^{\rm d}$ and an amplitude of $\Delta V=0.09$ mag.

AP 19 (=V531 Per, HE 622): Prosser et al. (1993b) discovered its optical band variability with a period of $P=0.80^{\rm d}$ and an amplitude of $\Delta V=0.045$ mag.

AP 32 (=HE 684): the optical band variability was discovered independently by Marilli et al. (1997) and O'Dell et al. (1997) who found the same period of $P=0.75^{\rm d}$ and $\Delta V$ amplitudes of 0.065 and 0.03 mag, respectively.

AP 43: Stauffer et al. (1985) discovered optical band variability with $P=0.56^{\rm d}$ and $\Delta V=0.10$ mag.

AP 93: Prosser et al. (1993a) discovered optical band variability with $P=0.62^{\rm d}$ and $\Delta V=0.10$ mag.

AP 193: the optical band variability was discovered by O'Dell et al. (1997) who found a period of $P=0.75^{\rm d}$ and a $\Delta V$ amplitude of 0.03 mag.

AP 244: Prosser et al. (1993b) discovered its optical band variability with a period of $P=0.96^{\rm d}$ and a $\Delta V$ amplitude of 0.04 mag. The period $P=0.46^{\rm d}$ found in this monitoring, is half than the previous determination. It may result from the relatively short observing time interval.