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Astron. Astrophys. 350, 513-516 (1999)

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2. Observations

The earlier V 368 Cep photometry consists of that in Poretti et al. (1985), Nations et al. (1990), Bianchi et al. (1991), Heckert et al. (1990), Chugainov et al. (1991, 1993), and Mantegazza et al. (1992). Of these, only Bianchi et al. (1991) and Mantegazza et al. (1992) published their numerical values. The first part of the data in Mantegazza et al. (1992) is from Poretti et al. (1985), while the Chugainov et al. (1993) photometry is from Chugainov et al. (1991). HD 219522 and HD 219285 were used as the comparison ([FORMULA]) and check star ([FORMULA]) of the differential photometry by Bianchi et al. (1991) and Mantegazza et al. (1992). The [FORMULA] and [FORMULA] of [FORMULA], which have been measured only once (Mantegazza et al. 1992), were added to the differential magnitudes from Bianchi et al. (1991). Finally, two possibly erroneous V magnitudes on [FORMULA] and 367.248 were removed from Mantegazza et al. (1992).

Our new UBVR photometry was made with the 60 cm telescope at Tashkent Observatory during 68 nights between June, 1991 and November, 1991. The nightly extinction coefficients and transformations into the standard Johnson UBVR system were determined by standard star measurements. Every observation is the mean of [FORMULA] integrations in each filter. The external accuracy is about [FORMULA] in BVR and [FORMULA] in U.

Table 2 summarizes the combined earlier and new photometry, and specifies the separately analysed subsets. The whole UBVRI photometry is published only  in electronic form (hereafter Table 5). Given the accuracy in Bianchi et al. (1991), the BV precision for [FORMULA]([FORMULA]), and the unknown error for each individual measurement, reasonable error estimates for the whole data in Table 5 are [FORMULA] in BVRI and [FORMULA] in U. Note that the U and [FORMULA] in Table 5 during SET=3, 4 and 5 are magnitude differences between V 368 Cep and HD219522.


[TABLE]

Table 2. The collected V 368 Cep photometry: The observing time interval, the subset (SET), the observatory, the primary comparison star ([FORMULA]), the secondary comparison star ([FORMULA]), the reference and the number of observing nights (nts)


The detection procedure by Jetsu et al. (1993) revealed two probable photometric flares on [FORMULA] (SET=6: Flare) and 482.4540 (SET=7: Flare?), i.e. no U-band measurement was available for the latter event. These two events may also represent observational errors, since an indisputable identification would require more than one flare measurement in UBV, like in Jetsu et al. (1993: Figs. 1-3). Optical flares have been detected in several late-type main sequence stars (Haisch et al. 1991), but rarely in late-type subgiants or giants (Henry & Newsom 1996).

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© European Southern Observatory (ESO) 1999

Online publication: October 4, 1999
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