COMMISSION 27 OF THE I.A.U.
                 INFORMATION BULLETIN ON VARIABLE STARS
                             Number 3262

                                                        Konkoly Observatory
                                                        Budapest
                                                        11 November 1988

                                                        HU ISSN 0374 - 0676


                  BV PHOTOMETRY OF IOTA BOOTIS

The light variability of iota Bootis was firstly reported by Guthnick
and Prager (1918). Based on two short data series Albert (1980) suggested
a 35-40 minute period with 0.025 magnitude variation in B. Kholopov et al.
(1985) reported this star as DSCTC type.
   Our observations were made on four nights in June 1988 with the 40 cm
Cassegrain reflector of JATE University at the Baja Observatory described
by Hegedus (1987),
   Iota Boo (=21 Boo=HR 5350=HD 125161=ADS 9198=NSV 06610, V=4.75m A7V)
was observed as var2 during a photometric study of the delta Scuti type star
kappa2 Boo. Iota Boo is a visual binary, A and B components were observed
together.
  The comparison star was theta Boo (=23 Boo=HR 5404=HD 126660=NSV 06669,
V=4.05m F7V). Although it is a suspected variable (Kukarkin et al. 1982),
probably is not delta Scuti star.
  The iota Boo A+B - theta Boo differential light curves in the instrumental
BV system are presented in Figure 1. By use of the Fourier analysis of
unequally spaced data (Deeming, 1975), the power spectra for all our data
were calculated. Table. I shows the peaks in the spectrum of the DeltaV light
curve. The frequency spectrum for DeltaB is similar, but there are differences
in the position of frequencies.


                  Table I

      frequency (c/d)    amplitude (mag)

f_1       2.822             0.016
f_2       9.279             0.014
f_3      13.675             0.012
f_4      22.660             0.012
f_5      36.782             0.013


                            [FIGURE 1]

 Figure 1. iota Boo A+B - theta Boo light curves on four nights. O signs are
           the averages: <DeltaV>=0.6996m, <DeltaB>=0.4784m, 
           <DeltaB-V>=-0.2212m. Data are in IAU Archives as file 167.


   In the case of f_2, f_3 and f_4 the determination of the true frequencies
is difficult because the 1 c/d aliases have similar peak-heights. We note
that f_2+f_3~f_4 and f_3+f_4~f5. The short period P_5=38-39 minutes is very
close to Albert's result.
   Our observations were also analysed by the Maximum Entropy Method (Burg,
1975; Ulrych and Clayton, 1976). The data were made equidistant by linear
interpolation. One or two peaks at the average period of 0.026 is present
on each night. The position of the other peaks at longer periods varies.
   There is an interesting group of the delta Scuti stars with such a short
period (0.021d<P<0.032d): V377 Cas, BG Cet, V624 Tau, V534 Tau, V650 Tau,
UU Com, rho Vir, gamma CrB and V 1644 Cyg. These stars have small amplitude and
very complex light variation.
   We conclude that iota Bootis may be really a delta Scuti star with a
characteristic short period P=0.027d+-0.002d = 39+-3 minutes. More 
observations are needed to determine its periodic behaviour.


                  K. SZATMARY

                JATE University
                   Dom ter 9.
             H-6720 Szeged, Hungary



References:

Albert, J.: 1980, JAAVSO 9, No. 1, p. 20. [BIBCODE 1980JAVSO...9...20A ]
Burg, J.P.: 1975, Ph.D. Thesis, Stanford University
Deeming, T.J.: 1975, Astrophys. Space Sci., 36, 137. [BIBCODE 1975Ap&SS..36..137D ]
Guthnick, P., Prager, R.: 1918, Veroff. Berlin Babelsberg, H.3, p. 113.
Hegedus, T.: 1987, IBVS No. 3125.
Kholopov, P.N., Samus', N.N., Kazarovets, E.V., Perova, N.B.: 1985, IBVS No. 2681.
Kukarkin, B.V. et al.: 1982, New Catalogue of Suspected Variable Stars, Nauka,
   Moscow [BIBCODE 1982ncsv.book.....K ]
Ulrych, T.J., Clayton, R.W.: 1976, Phys. Earth Planet. Inter., 12, 188. [BIBCODE 1976PEPI...12..188U ]


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