2 Observations

2.1 New observation

During 1994 and 1995, OJ 287 was observed with the 1-m RRC telescope at Yunnan Observatory, which is equipped with a direct CCD camera at the Cassegrain focus, and the 1.26-m Infrared telescope at Xinglong station of Beijing Observatory. The daily averaged magnitudes are presented in Tables 1 and 2. The data reduction and the detailed magnitudes will appear in separate papers altogether with other BL Lac objects observed during the same period (Bai et al. 1998, for the optical data and Xie et al. 1998, for infrared data).

  

Table 1: Daily averaged magnitudes of OJ 287

  

Table 2: Daily averaged magnitudes of OJ 287

2.2 Historic observations

Since no infrared observation is available before 1971, and in order to compare the optical data with the infrared data, only the observations in optical band after 1971 have been compiled (Martynov 1971; Huruhata 1971; Burkhead 1971; Locher 1972; Strittmatter et al. 1972; Craine & Warner 1973; Goldsmith & Weistrop 1973; Visvanathan 1973; Frohlich et al. 1974; Selmes et al. 1975; Veron & Veron 1975; Kikuchi et al. 1976; O'Dell et al. 1978a,b; Usher 1979; Hagen-Thorn et al. 1980; Pushell & Stein 1980; Shaefer 1980; Gaida & Roser 1982; Takalo 1982; Haarala et al. 1983; Bortle 1983a,b; Sitko et al. 1983; Corso et al. 1984, 1986, 1988; Holmes et al. 1984a; Moles et al. 1984, 1985; Sillanpaa et al. 1985; Sitko et al. 1985; Sitko & Junkkarinen 1985; Brindle et al. 1986; Cayatte et al. 1986; Miller 1987; Monella 1987; Monella & Verdenet 1987; Sillanpaa 1987; Smith et al. 1987; Xie et al. 1987, 1988a,b, 1989, 1990, 1991, 1992, 1994; Sillanpaa 1988a,b; Webb et al. 1988; Brown et al. 1989; Takalo 1989; Mead et al. 1990; Takalo et al. 1990; Sillanpaa et al. 1991a,b; Sitko & Sitko 1991; Takalo 1991; Takalo et al. 1992a; Valtaoja et al. 1991; Carini et al. 1992; Kidger & Takalo 1993; Okyudo 1993; Smith et al. 1993; Fiorucci & Tosti 1994a,b; Meusinger 1994a,b; Vanmunster & Cautern 1994; Kidger 1995; Arimoto et al. 1997). All those data and the data presented in Table 1 are used in our analysis. The data in UBVRI bands are shown in Figs. 1a-e.

The infrared (JHK) are from Epstein et al. (1972), Rieke et al. (1977), O'Dell et al. (1977, 1978a), Pushell & Stein (1980), Allen et al. (1982), Wolstencroft et al. (1982), Impey et al. (1982, 1984), Sitko et al. (1983), Holmes et al. (1984a,b), Brindle et al. (1986), Gear et al. (1986a,b), Landau et al. (1986), Roelling et al. (1986), Smith et al. (1987), Impey & Neugebauer (1988), Brown et al. (1988), Lorenzetti et al. (1989), Mead et al. (1990), Takalo et al. (1992b), Bersanelli et al. (1992), Sitko & Sitko (1991), Gear (1993), Kidger et al. (1994), Litchfield et al. (1994). Some early data are derived from the figure of Soifer & Neugebauer (1980). The infrared (JHK) data are shown in Figs. 2a-c.

  

Figure 1: a) The long-term U light curve of OJ 287 covering the period 1971-1991, there are no new data available in the literature after 1991. b) The long-term B light curve of OJ 287 from 1971 to 1995. c) The long-term V light curve of OJ 287 from 1971 to 1996. d) The long-term R light curve of OJ 287 from 1972 to 1996. e) The long-term I light curve of OJ 287 from 1972 to 1996

  

Figure 2: a) The long-term J light curve of OJ 287 in covering a period of 1975 through 1995, the discontinuity of the light curve is due to the lack of observation in this band. b) The long-term H light curve of OJ 287 covering a period of 1972 through 1995, the discontinuity of the light curve is due to the lack of observation in this band. c) The long-term K light curve of OJ 287 covering a period of 1971 through 1995, the discontinuity of the light curve is due to the lack of observation in this band

2.3 Variations

From the available literature, we found that the variations in the UBVRIJHK bands are: $\Delta U = 4\hbox{$.\!\!^{\rm m}$}72 (11\hbox{$.\!\!^{\rm m}$}86 - 16\hbox{$.\!\!^{\rm m}$}58)$; $\Delta B = 5\hbox{$.\!\!^{\rm m}$}93 (12\hbox{$.\!\!^{\rm m}$}47 - 18\hbox{$.\!\!^{\rm m}$}40)$; $\Delta V = 5\hbox{$.\!\!^{\rm m}$}18 (12\hbox{$.\!\!^{\rm m}$}22 - 17\hbox{$.\!\!^{\rm m}$}40)$; $\Delta R = 4\hbox{$.\!\!^{\rm m}$}45 (12\hbox{$.\!\!^{\rm m}$}25 - 16\hbox{$.\!\!^{\rm m}$}70)$; $\Delta I = 4\hbox{$.\!\!^{\rm m}$}07 (11\hbox{$.\!\!^{\rm m}$}73 - 15\hbox{$.\!\!^{\rm m}$}80)$; $\Delta J = 3\hbox{$.\!\!^{\rm m}$}87 (10\hbox{$.\!\!^{\rm m}$}73 - 14\hbox{$.\!\!^{\rm m}$}60)$; $\Delta H = 3\hbox{$.\!\!^{\rm m}$}78 (9\hbox{$.\!\!^{\rm m}$}94 - 13\hbox{$.\!\!^{\rm m}$}73)$; $\Delta K = 3\hbox{$.\!\!^{\rm m}$}54 (8\hbox{$.\!\!^{\rm m}$}81 - 12\hbox{$.\!\!^{\rm m}$}75)$. The color indices are respectively: $U-B = -0.60 \pm 0.14$ (N = 391 pairs); $B-V = 0.46 \pm 0.17$ (N = 470 pairs); $B-I = 1.42 \pm 0.25$ (N = 186 pairs); $V-R = 0.48 \pm 0.14$ (N = 243 pairs); $V-I = 0.98 \pm 0.22$ (N = 235 pairs); $R-I = 0.56 \pm 0.12$ (N = 198 pairs); $J-H = 0.82 \pm 0.16$ (N = 173 pairs); $H-K = 0.88 \pm 0.14$ (N = 193 pairs); $J-K = 1.70 \pm 0.19$ (N = 173 pairs).

From our observations presented in Table 1, a correlation has been found for B-V and V (see Fig. 3): $V= - (1.02\pm0.08)(B-V)+(15.61\pm 0.01)$ with a correlation coefficient r= -0.831. This correlation means that the spectrum flattens when the source brightens.

  

Figure 3: Color index-(B-V) versus against V magnitude. The relation suggests that the spectrum changes with the brightness of the source