1. Introduction

The FK Comae-type stars were defined as single and rapidly rotating G-K giants with strong chromospheric and transition region UV emission (Bopp & Rucinski 1981; Bopp & Stencel 1981). The rapidly rotating post-main-sequence star V 1794 Cyg  (HD 199178, G5III-IV, $P_{\mathrm{phot}} \!=\! 3\hbox{$.\!\!^{\rm d}$ }337484$, $v \sin{i} = 65.4$ km s^-1) is one of the original candidates for this class (Herbig 1958; Jetsu et al. 1990a, Paper  I; Fekel 1997). V 1794 Cyg seems to have no binary companion, because the radial velocity is nearly constant (Huenemoerder 1986: $v_{\mathrm{rad}} = -27.9 \ \pm\ 1.6$ km s^-1). Jetsu et al. (1990b, Paper  II) combined new data with all earlier photometry of V 1794 Cyg (Bopp 1982; Bopp et al. 1983; Kaluzny 1984; Nations & Seeds 1986; Huovelin et al. 1987). Those data between 1975 and 1989 were analysed in Paper  I. Since then additional photometry of V 1794 Cyg have been published (e.g. Heckert & Stewart 1992; Rodono & Cutispoto 1992; Dempsey et al. 1992). We present new photometry of V 1794 Cyg made between 1989 and 1995 at the Mount Hopkins Observatory, the Mount Maidanak Observatory, the Mount Laguna Observatory, the Kvistaberg Observatory, and the Royal Swedish La Palma Observatory. This paper presents the methods applied to guarantee the homogeneity of these data between 1975 and 1995, which are analysed in Jetsu et al. (1999, Paper  III). The following topics are discussed: the division of the V 1794 Cyg data into 114 subsets (SET: Sect. 2), the secondary comparison stars (C₂: Sect. 3), the primary comparison stars (C₁: Sect. 4), and the previous and the new photometry of V 1794 Cyg (Sects. 5 and 6). The photometric measurements of the primary and secondary comparison stars have been compiled into Tables 1 and 2, respectively. The necessary SET information of the V 1794 Cyg data is summarized in Table 3. Finally, the collected photometry of V 1794 Cyg is given Table 4, which is only available in electronic form (see Grewing et al. 1992).

   

Table 1: The UBVRI magnitudes of all C₂, and their weighted means

16 Cyg B
U	B	V	R	I	Reference
$7.060 \pm 0.026$	$6.860 \pm 0.019$	$6.200 \pm 0.017$			Johnson & Morgan 1953
$7.090 \pm 0.031$	$6.900 \pm 0.023$	$6.210 \pm 0.022$			Tolbert 1964
$7.070 \pm 0.019$	$6.880 \pm 0.014$	$6.220 \pm 0.011$			Argue 1966
$7.072 \pm 0.043$	$6.855 \pm 0.043$	$6.191 \pm 0.013$	$5.750 \pm 0.016$	$5.408 \pm 0.016$	Johnson et al. 1966
	$6.898 \pm 0.022$	$6.238 \pm 0.020$	$5.692 \pm 0.023$	$5.341 \pm 0.027$	Moffett & Barnes 1979
		$6.217 \pm 0.010$			Tedesco et al. 1982
		$6.230 \pm 0.009$			Olsen 1983
		$6.200 \pm 0.010$			Campins et al. 1985
	$6.910 \pm 0.028$	$6.250 \pm 0.020$	$5.716 \pm 0.028$	$5.350 \pm 0.028$	Rakos & Franz 1988
		$6.232 \pm 0.004$			Fabregat & Reglero 1990
		$6.242 \pm 0.008$			Stetson 1991
	$6.876 \pm 0.017$	$6.215 \pm 0.016$			Turon et al. 1992
		$6.238 \pm 0.004$			Skiff 1993
$7.071 \pm 0.010$	$6.882 \pm 0.015$	$6.230 \pm 0.013$	$5.728 \pm 0.025$	$5.383 \pm 0.031$	Weighted mean for 16 Cyg B
57 Cyg
	$4.630 \pm 0.023$	$4.780 \pm 0.018$			Ljunggren & Oja 1964
$4.044 \pm 0.023$	$4.625 \pm 0.023$	$4.766 \pm 0.022$	$4.833 \pm 0.023$	$4.968 \pm 0.025$	Johnson et al. 1966
$4.025 \pm 0.023$	$4.635 \pm 0.017$	$4.760 \pm 0.014$			Eggen 1968
$4.100 \pm 0.026$	$4.660 \pm 0.021$	$4.800 \pm 0.019$			Crawford et al. 1971
		$4.740 \pm 0.010$			Straizys et al. 1989
	$4.640 \pm 0.009$	$4.774 \pm 0.007$			Turon et al. 1992
$4.053 \pm 0.031$	$4.639 \pm 0.009$	$4.766 \pm 0.017$	$4.833 \pm 0.023$	$4.968 \pm 0.025$	Weighted mean for 57 Cyg
SAO 50257
		$6.660 \pm 0.010$			Straizys et al. 1989
	$7.554 \pm 0.152$	$6.634 \pm 0.022$			Turon et al. 1992
	$7.554 \pm 0.152$	$6.656 \pm 0.010$			Weighted mean for SAO 50257
SAO 50326
$9.990 \pm 0.010$	$8.730 \pm 0.008$	$7.540 \pm 0.006$			McClure 1970
$10.010 \pm 0.027$	$8.720 \pm 0.020$	$7.560 \pm 0.008$			Landolt 1975
		$7.540 \pm 0.010$			Straizys et al. 1989
$9.992 \pm 0.007$	$8.729 \pm 0.003$	$7.546 \pm 0.009$			Weighted mean for SAO 50326