Astron. Astrophys. 364, 641-645 (2000)

2. Observations

The detection of intrinsic small-scale light fluctuations in stars is hampered by atmospheric disturbances and instrumental imperfections. These limitations present an often insuperable barrier to observers operating with a single telescope. Such difficulties, however, may be overcome by the simultaneous use of several telescopes. The key idea contributed by the synchronous network of optical telescopes is as follows: operations of distant telescopes are synchronized to UTC time within the sampling time; consequently, the different datasets can be considered as sets with the same valid signal and uncorrelated atmospheric and photon noises. In this case, using available statistical procedures for simultaneous photometer readings, it is possible to identify instrument faults, to increase the signal-to-noise ratio and to detect signals that may be comparable to that contributed by intrinsic noise sources.

The observational data for the flare star EV Lac reported here were obtained from four separate sites over 19 nights in September-October 1998. The instruments which were used were the following:

• the 2 m Ritchey-Chretien and the 60-cm Cassegrain telescopes at Peak Terskol (North Caucasus, 3100 m a.s.l.) with a high-speed two-channel UBVR photometer (Zhilyaev et al. 1992);

• the 30 inch telescope at Stephanion Observatory in Greece, equipped with a single-channel photometer with digitized readings in the B band (Mavridis et al. 1982);

• the 1.25 m reflector AZT-11 at the Crimean Observatory with a UBVRI photometer-polarimeter (Kalmin & Shakhovskoy 1995);

• the 60-cm Cassegrain telescope at the Belogradchik Observatory with a single-channel UBV photon-counting photometer (Antov & Konstantinova-Antova 1995).

The typical integration time was 0.1 s. For low amplitude flare events the readings were rebinned to 0.6, 1.0 or 1.2 s. The sky background was subtracted from all the data presented here. The UB data were converted to a relative intensity scale with respect to the mean values of quiescent fluxes.

More than a dozen flare events were observed on EV Lac in UBVRI during the observation period. Three events were selected for the present paper. Two of these were registered at more than one site using distant telescopes operating synchronously to an accuracy of 0.1 s.

© European Southern Observatory (ESO) 2000

Online publication: January 29, 2001
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