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\IBVShead{4237}{30 August 1995} 
\title{BV PHOTOMETRY OF THE DELTA SCUTI STAR IOTA BOOTIS} 
\begintext

The light variation of Iota Bootis (= 21 Boo = NSV\,06610 = HR\,5350) was
discovered by Albert (1980). Based on his data he concluded that Iota Bootis
may be a Delta Scuti-type variable with a very short period (about 40
minutes). Szatm\'{a}ry (1988) had similar result, which was confirmed by
G\'{a}l et al. (1994). Unfortunately these measurements had very limited
accuracy therefore only the existence of the variation with a period close
to 40 min. was demonstrated.

We carried out photoelectric photometry (through B and V filters) on two
nights, 24 and 26 May, 1995 with the 40 cm Cassegrain type telescope of
Szeged Observatory using an SSP-5A photometer. The comparison star was HR
5360. The main aim of our measurements was to determine the exact period of
variation and its amplitude in B and V. On these two nights we collected 155
points in two colors which cover about 10 cycles of the light curve (the
individual observations are available through e-mail -- see below).

In order to determine the exact period of variation we calculated the
Fourier-transform (DFT) of B and V light curves separately and the phase
dispersion spectra (PDM) too. The results  in the
different colors and with different methods are in agreement with each other
 (the variance is about
0.0002-0.0003 day). The correct value of the period is 0.0276 day (39.7
min) with an estimated error of $\pm $ 0.0003 day (0.4 min).

We plotted the averaged Fourier spectrum of B light curves in Figure 1. The
period can be better determined with this averaging because the amplitude
of noise decreases relatively to the highest peak (G\'al et al., 1994). The
phase diagram can be seen in Figure~2.

The Fourier amplitudes of the light variation are 0.007 and 0.005 magnitude
in B and V, respectively. We fitted a sine function to the light curves in
B (because of their regularity and higher S/N ratio) which are plotted in
Figure~3.

The fitted function is

$$
\Delta B=-1.291+0.007\sin (2\pi \cdot 36.231884\cdot T+2.7), 
$$

\noindent where the frequency is in c/d, the phase is in radian and T means
HJD$-$2440000.

We can conclude that the photometric period of Iota Bootis is 0.0276 $\pm $
0.0003 day (=39.7 $\pm $ 0.4 min) which value  confirms the results
of previous studies. The full amplitudes are 0.015 and 0.010 magnitude in B
and V, respectively, which show that this variation is very close to our
limited accuracy. Therefore more accurate (0.001 magn. precision)
photoelectric measurements are recommended.

The mode identification is difficult. In the case of double star Tau Cygni
(Mkritichian et al., 1995) which has very similar light variation, the
density determined from the orbital period gave a possibility to calculate
the pulsational constant and comparing with the theory the excited mode
could be estimated.
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\centerline{2}
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\centerline{\epsffile{4237-f1.ps}}
\centerline{Figure 1. The mean Fourier spectrum of the B light curves}

\epsfysize=9cm
\centerline{\epsffile{4237-f2.ps}}
\centerline{Figure 2. The phase diagram of Iota Bootis (P=0.0276 day, $T_{0}$= HJD\,2449800.01)}
\vfill \eject

\centerline{3}
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\centerline{\epsffile{4237-f3.ps}}
\begin{center}Figure 3. The 24 May (upper panel) and 26 May (lower panel) light curve with the fitted sine curve
\end{center}


\vskip 5mm

The author wishes to express his thanks to Drs K. Szatm\'ary and J. Vink\'o
for their useful suggestions and advice. This work has been supported by
Hungarian OTKA\ Grants No.4330 and No.\,7522, Foundation of Pro Renovanda Cultura
Hungariae, `Di\'akok a tudom\'any\'ert' Grant Dt. 1995/30 and Szeged
Observatory Foundation.

\vskip 1cm

\beginauthors
\authorsrightcol
L.L. KISS 
Dept. of Experimental Physics
JATE University
SZEGED, D\'om t\'er 9.
H-6720 Hungary
Internet: L.Kiss@physx.u-szeged.hu \
\endauthors

\references

Albert, J.: 1980, {\it Journal of AAVSO}, {\bf 9}, No.1, 20

G\'al, J., Szatm\'ary, K., Vink\'o, J.: 1994, {\it IBVS} No. 4071

Mkritichian, D.E., Fedotov, Yu.T., Romanov, Yu.S.: 1995, {\it Delta Scuti
Star Newsletter}, 8, 16
%Original: Star Newsletter }Issue 8, 16
%Modified: Mon Sep 26 13:18:09 MEST 2005

Szatm\'ary, K.: 1988, {\it IBVS} No. 3262
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