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Astron. Astrophys. 327, 1114-1122 (1997)

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2. Observations and reduction method

The data presented in this paper were collected from 1967 to 1977 by using four telescopes at the Serra La Nave (SLN) mountain station of Catania Observatory recently dedicated to Mario G. Fracastoro: a 91-cm Cassegrain reflector, a 61-cm quasi-Cassegrain reflector, and two 30-cm Cassegrain reflectors. All telescopes were equipped with similar photometers with uncooled EMI 6256 photomultipliers (S13 spectral response) and a combination of Schott filters to match the standard U B V Johnson system.

2.1. Flare monitoring data

The data acquired during the flare monitoring, originally recorded on strip-charts, were reduced according to the following procedure: we used a scanner to generate electronic images of the portions of the strip-charts where flares were recorded. Flare data were then extracted from these images and reduced by means of an IDL procedure (FLRED) we specifically developed for this purpose.

A total monitoring time of 1272 h was collected: 903, 1013, and 864 h of which were in U, B, and V bands, respectively. The sum of time coverage in the three bands exceeds the effective total coverage because the observations were generally done in more than one filter. A total of 254 flare events were detected, 212, 170, and 128 of which in the U, B, and V bands, respectively. Details on the time coverage, number of observed flares and occurence rate in each band and year are given in Table  1.


Table 1. Number of flares (Nfl), total coverage time (T), and mean flare occurrence rate (R).

The following quantities were measured for each flare in each band: time of light maximum (UTmax ), luminosity at maximum ([FORMULA] ), integrated energy (E ), rise-time to the highest peak ([FORMULA] ), duration of the light decrease to quiescence (da ), flare amplitude ([FORMULA] ). The flare energies (E ) were derived from the quiescent EV Lac luminosity (L ) times the equivalent duration (P ):


where L = 5.01 [FORMULA], 3.49 [FORMULA], 7.84 [FORMULA], in U, B, and V, respectively, as derived from flux calibration by Gershberg & Chugainov (1969) by assuming a distance of 5 pc (Gliese 1969) and U=12.89, B=11.83, V=10.25 (Andrews & Chugainov 1969) for the quiescent magnitudes of EV Lac. The equivalent duration (P ) is defined as


where [FORMULA] and [FORMULA] are the intensities of the star in its quiescent and flaring states, respectively.
Individual flare data are given in Table 2 that is only available in electronic form at the CDS.

2.2. Rotation modulation data

To derive the outside of flare seasonal light curves of EV Lac, differential measurements were sparsely done during the course of the flare monitoring. In 1967-68, BD+42 4527 was used as comparison star. However, this star was found to be a semiregular red variable ([FORMULA] Ori-type). Therefore, beginning in 1969, BD+43 4299, BD+43 4303 and BD+43 4304 were used as comparison stars, following Andrews & Chugainov (1969). Reliable and more extended data to build seasonal light curves of EV Lac were secured only from 1969 to 1972. A summary of these observations is given in Table  3.


Table 3. Log of the data used for rotational modulation analysis

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© European Southern Observatory (ESO) 1997

Online publication: April 6, 1998