P1724 is a recently reported, X--ray active PMS star (Preibisch et al. 1995).
Neuhäuser et al. (1995) found an X--ray variability with modulation
on a 
20 hour time scale in the star and
speculated that the variability was the result of rotational modulation.
P1724 was monitored from MTSB on 17 nights over a six week period.
About five observations were made per night using V, R and I filters.
Three field stars were used for comparison (see
Figure 3). The results
of these observations are shown in Figure 4.
One can see from the figure the effects of aliasing.
There is a family of several periods indicated by the periodogram.
The preferred frequency is 1.18 rotations per day (a 0.85 day long
period), but the power at this peak is not particularly stronger than
the three other strong peaks. However, the 1.21 day period (0.826 rotations per
day) is excluded by the nightly trend analysis. In this case, the
trend of the data is opposite to the direction of the fit (see
Figure 5). Evaluation of the 5.5 day period is
more difficult. The dispersion of the data in any given night is
only 10% greater than that of the 0.85 day solution. However, when
the data are fit to the 5.5 day period, each given night has the mild
trend, expected from the shorter period. Only one field standard star
was available for the TAP 26 field. This, and the fact that the signal
to noise is higher for P1724, are the reasons for the
much cleaner results of the P1724 periodogram with respect to that of
TAP 26.
