COMMISSIONS 27 AND 42 OF THE IAU
                INFORMATION BULLETIN ON VARIABLE STARS
                             Number 4071

                                                Konkoly Observatory
                                                Budapest
                                                17 August 1994

                                                HU ISSN 0374 - 0676

                 PHOTOMETRIC PERIOD OF THE SUSPECTED
                  DELTA SCUTI-TYPE STAR IOTA BOOTIS


  Iota Boo (= 21 Boo = NSV 06610 = HR 5350) is a suspected low-amplitude DSCTC-
type variable according to Kukarkin et al. (1982) and Kholopov et al. (1985). In spite of
the photometric variability reported by Albert (1980) this star was used several times as
a photometric standard (e.g. Glushneva, 1992), but it was neglected as far as the study
of its light changes is concerned. Albert's result was more or less confirmed by Szatmary
(1988) but no other analysis of the light curve has been published yet. We note that
some references for this star given e.g. in the SIMBAD database correspond to 44i Boo,
a bright W UMa-type eclipsing binary, instead of Iota Boo.
  We carried out photoelectric photometry (in Johnson-system using B and V filters) of
Iota Bootis on three nights: 29 June, 8 and 9 July, 1993 with the 40 and 50 cm Cassegrain
telescope of Szeged Observatory and Konkoly Observatory, respectively. The comparison
and check stars were Theta Boo (HR 5404) and HR 5360, respectively. There were 
simultaneous observations on the last night at the two observing sites located in 200 km
distance from each other. The aim of this short campaign was to separate the light variation 
of Iota Boo from the atmospheric effects and re-check the photometric period(s)
found by Albert (1980) and Szatmary (1988). Unfortunately, the light curves obtained
have only limited accuracy (0.02-0.03 mag) due to instrumental problems and weather
conditions, therefore these curves are mainly dominated by observational noise. However,
the multi-site observations enabled us to filter out the noise and detect a frequency 
component which is very probably due to rapid oscillation of Iota Boo. We used the raw
(variable star minus sky) data for period analysis.
  The method used for noise-filtering has been known in data processing for a long time
and based on the following: if we compute Fourier spectra of different light curves of a
variable star and then superimpose, the amplitude of the noise decreases relative to the
amplitude of the real oscillation, because the peaks caused by the noise are not, exactly
at the same position in the different spectra, in contrast with the oscillation peak. In
other words, we can "average out" the noise relative to the signal. It is important to note
that the signal-to-noise ratio cannot be increased and the amplitude of the oscillation, of
course, cannot be determined properly by this method.
  The sum of the spectra is plotted in Figure 1 (based on both V and B data because
the position of the oscillation peak does not depend on the wavelength). As it can be
seen, there is a peak at 35.6 c/d (about 40 min period) in the summed spectrum of
Iota Boo which is in good agreement with the results of previous studies. Meanwhile,
the composite spectra of the comparison stars do not show peak at the given frequency
interval. Therefore we conclude that Iota Boo definitely shows low-amplitude oscillation
with the period mentioned above. The amplitude of the oscillation is close to the errors of
our measurements, and probably does not exceed 0.05 mag. This means that the variation
and the presumable type of Iota Boo (DSCTC) is also confirmed.


                                [FIGURE 1]

       Figure 1. Sum of the spectra. The continuous line represents
       the spectrum of Iota Boo, while the dashed and dotted lines
       show the spectrum of comparison and check star, respectively.


 This work has been supported by Hungarian OTKA Grants No. F7318, T4330 and
the doctoral scholarship of J. Gal from the Foundation for the Hungarian Science. We
would like to express our thanks to the staff of Konkoly Observatory for kindly granting
telescope and computer time.


                        J. GAL, K. SZATMARY
                        Dept. of Experimental Physics

                        J. VINKO
                        Dept. of Optics
                        JATE University
                        SZEGED, Dom ter 9.
                        H-6720 Hungary
                        Internet: J.Gal@physx.u-szeged.hu



References:

Albert, J.: 1980, Journal of AAVSO, 9, No. 1, 20 [BIBCODE 1980JAVSO...9...20A ]
Glushneva, I.N.: 1992, Astron. Zu., 69, 1062 [BIBCODE 1992AZh....69.1062G ]
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 ]
Szatmary, K.: 1988, IBVS No. 3262