COMMISSION 27 OF THE I.A.U.
                 INFORMATION BULLETIN ON VARIABLE STARS
                             Number 3290

                                                         Konkoly Observatory
                                                         Budapest
                                                         9 February 1989

                                                         HU ISSN 0374 - 0676


            VARIABILITY OF LR Hya = HD 91816 NOT CONFIRMED

Bopp et al. (1984) found this star to be a new BY Draconis variable with a
photometric period of 3.1448 days and an amplitude of 0.02 mag in V. The
star is a double-lined spectroscopic binary with two nearly identical K0 dwarfs
and an orbital period of 6.866 days (Fekel et al. 1988). CaII 3950 A region
spectra show composite H and K emission features at a surface-flux level of
several 10^6 erg cm^-2s^-1. The photometric variability is thought to be
caused by the presence of starspots rotating in and out of view. As a result
of this, Kholopov et al. (1987) assigned the new variable star designation LR
Hya.
   Follow-up photometry has been obtained with the Fairborn APT (Automatic
Photoelectric Telescope) in 1984-85 (Strassmeier et al. 1989). Their
photometry revealed three different possible periodicities of 2.57, 3.57, and
4.86 days. The largest of these, at 4.86 days, results in the greatest
reduction of the sum of the squares of the residuals. The formal value of the
full amplitude from a sine-curve fit was ~0.04+/-0.02 mag in V, thus, not 
really significant.
   New photometry was obtained during the observing seasons 1986-87 and 1987-88
with the 0.25 m Fairborn APT and the 0.4 m Vanderbilt APT. All observations
used HD 91566 = SAO 137648 as the comparison star. A listing of the individual
data transformed to the UBV system can be requested from the author.
   The data were examined for periodicity using a period-finding program that
uses least-squares to fit sine curves to the data. No single significant
period for any of the data sets showed up. This is demonstrated in the
periodograms in Figure 1, where the three panels are for the 1986-87 and
1987-88 observing season, and for the combined data set from 1984 through 1988.
The arrows indicate the orbital period and half of the orbital period.
   The light curves are plotted with the orbital period of 6.866 days in Figure
2, where zero phase is taken arbitrarily as JD 2,446,800. A Fourier analysis,
allowing only for cosTheta and cos2Theta terms and using the orbital period
resulted in the (formal) amplitudes listed in Table 1. This table also lists
the seasonal mean differential brightnesses, their standard deviations, i.e.
its "width" or "variability" around that value in Figure 2 and, in the last
column, the average deviations or mean absolute deviations of the seasonal mean
brightness (all values in magnitudes).
seen by



                              [FIGURE 1]

 Fig. 1  Periodograms for the observing seasons 1986-87 and 1987-88 (top 
 and middle panel), and the combined data set of Table 1 from 1984 through 
 1988 (lower panel). The arrows indicate the orbital period and half of 
 the orbital period. No firm conclusion can be made about a photometric 
 period.

                              [FIGURE 2]

 Fig. 2  Differential V light curves for observing seasons 1984-85 (upper 
 panel) through 1987-88 (lower panel). The data are phased together with 
 the orbital period and an arbitrarily chosen epoch.


                              TABLE 1

                  PARAMETERS FROM LEAST-SQUARES FITS

Observing   JD         Data         Full        Mean      Standard   Average
season      2440000+  points      amplitude   brightness  deviation  deviation

1984-85     6045        62     0.011+/-0.008    0.377      0.020       0.017
            6197
1985-86     6417        16     0.071+/-0.027    0.395      0.024       0.019
            6555
1986-87     6806       109     0.011+/-0.004    0.391      0.012       0.010
            6943
1987-88     7141        73     0.026+/-0.012    0.403      0.023       0.020
            7318

   From this, the photometric variability seen by Bopp et al. (1984) from 1982
through 1984 cannot be confirmed for the follow-up seasons 1984 through 1988.
It is, however, interesting to note that the seasonal mean differential
brightness is slowly decreasing, from 0.377 mag in 1984-85 to 0.403 mag in
1987-88. This might be an indication that there is a long-term starspot
activity. If the data contain low-amplitude rotational modulation it is
certainly smaller than our standard deviation of around 0.02 mag in V.
   High precision, milli-mag photometry is needed to answer whether LR Hya is a micro
variable or not.


               KLAUS G. STRASSMEIER

         Department of Physics and Astronomy
                Vanderbilt University
                 Nashville, TN 37235
                      U.S.A.



References:

Bopp, B.W., Hall, D.S., Africano, J.L., Goodrich, B.D., Henry, G.W., and
   Barksdale, W.S. 1984, IBVS, No. 2604.
Fekel, F.C., Gillies, K., Africano, J., and Quigley, R. 1988, A. J., 96, 1426. [BIBCODE 1988AJ.....96.1426F ]
Kholopov, P.N., Samus, N.N., Kazarovets, E.V., and Kireeva, N.N. 1987, 
   IBVS No. 3058.
Strassmeier, K.G., Hall, D.S., Boyd, L.J., and Genet, R.M. 1989, Ap. J. Suppl.,
   69, 000 (January). [BIBCODE 1989ApJS...69..141S ]