North et al. (1992) derived a precise rotational
period from Geneva photometry and previously published y photometry
especially that of Morrison & Wolff (1971) for the cool
magnetic CP star 108 Aquarii. Their ephemeris was
Figure 4: The v photometry of 108 Aqr plotted according to HJD (phase
origin) 
. Data from Morrison &
Wolff (1971) transformed to the Four College APT system are shown
as open circles, from Adelman & Knox (1994) as
closed squares, and from this paper as plus signs. Differences between
these data sets are seen, especially in the rising branch of the light
curves
Adelman & Knox (1994) obtained 48 uvby values with the FCAPT. When they used North et al.'s ephemeris and compared their data with that of Morrison & Wolff corrected for zero point shifts, they found generally good, but not perfect agreement. Although they were not able to improve the above ephemeris, comparison of their data with that of Morrison & Wolff indicated some changes in the shapes of the light curves especially a phase shift in the rising branch of the u curve which is less evident in v and b and a perhaps slightly greater amplitude in y. As this was similar to the changes in the shape of the light curves of 56 Ari reported by Adelman & Fried (1993) who interpret this type of behavior as due to free body precession of the magnetic CP star, additional photometric FCAPT observations of this star were made in the fall of 1995 using the same comparison and check stars. Almost all the 146 new observations observations were made during one month with many observations per night. Due to the stellar period and the telescope's observing window, only about 5% of the light curve could be covered each night.
The agreement of the average ch-c values with those of Adelman & Knox (1994) is good except for u which has a 0.010 mag offset. The ephemeris of North et al. (1992) also satisfies the new observations. These fall 1995 observations show clearly new features, especially a secondary minimum near phase 0.90 in u, v, and b in the midst of the broad maximum. Possibly it is now seen due to the superior definition of the light curve, which is a complicating factor in the entire analysis as are slight shifts in the ch-c star values.
Figure 4 (click here) shows the v magnitudes from Morrison & Wolff (1971) (open circles), Adelman & Knox (1994) (closed squares), and this paper (pluses). The newly found secondary minimum is seen well only in this paper's data. The falling branch values are in good agreement while the rising branch values are offset from one another, which was previously noted by Adelman & Knox. The new values suggest a narrower core for the secondary than do the previous photometry and near phase 0.6 a broader maximum.
As in Adelman & Knox a careful comparison with the Morrison & Wolff data is given, here I present a comparison between the current data and that published by Adelman & Knox (see Fig. 5 (click here)), which cover a period of 470 days. Slight adjustments in the values are made to correct offset in the data.
For u the rising branch near the primary maximum is now well defined. The rising branches are in reasonable agreement while the fall branches may be offset. For v and b the greatest differences are between phases 0.7 and 0.0, near the primary maximum and secondary minimum. For y the greater scatter of the Adelman & Knox (1994) data makes it difficult to come to any conclusions. The improved coverage of the light curve and reduction in scatter are important for future studies of 108 Aqr. To establish that the differences in the light curves are real requires additional data of the type presented in this paper.
Acknowledgements
This work was supported in part by NSF grant AST-9115114 to The Citadel and in part by grants from The Citadel Development Foundation. I appreciate the continuing efforts of L.J. Boyd and R.J. Dukes Jr., to keep the FCAPT operating properly.
Figure 5: The uvby photometry of 108 Aqr plotted according to HJD (phase
origin) with values from Adelman &
Knox (1994) as closed squares and from this paper as plus signs