3C454.3 is a widely studied and monitored flat spectrum radio quasar. We use the observations from the Small and Moderate Aperture Research Telescope System (SMARTS) to analyze the long-term optical and spectral variabilities of 3C454.3 at B, V, R, J, and K (BVRJK) bands. Based on the relation: , we calculate the multiband spectral indices () and analyze the relations between and , where is the flux density at band (=B, V, R, J, K). Main results are as follows. (1) The largest variations at BVRJK bands are B = 3.370.08 mag, with the timescale 1015 days, at B band; V = 3.310.07 mag, with the timescale 1014 days, at V band; R = 3.620.12 mag, with the timescale 679 days, at R band; J = 4.080.01 mag, with the timescale 763 days, at J band; and K = 5.030.03 mag, with the timescale 2715 days, at K band. (2) We analyze the long-term BVRJK lightcurves and obtain the quasiperiodicities: days, days, and years. (3) Multiband lightcurves show time delays: = days, = days, = days, and = days. (4) The relations between and show strong correlations, which are typical RWB behaviors; when the source turns to be brighter, the spectral indices turn to be redder.

中文翻译：

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FSRQ 3C454.3的长期光学和光谱变异性

3C454.3是广泛研究和监测的平面频谱无线电类星体。我们使用来自中小孔径研究望远镜系统（SMARTS）的观察结果，分析3C454.3在B，V，R，J和K（BVRJK）波段的长期光学和光谱变化。根据关系：，我们计算多频带光谱指数（）和分析之间的关系和，其中是在磁通密度带（= B，V，R，J，K）。主要结果如下。（1）BVRJK波段最大的变化是B = 3.37 0.08 mag，在B波段的时标为1015天; V = 3.31 0.07 mag，在V波段的时标为1014天；R = 3.62 0.12 mag，在R波段的时标为679天；J波段J = 4.08 0.01 mag，时标763天 ; 和K = 5.03 0.03 MAG，与时间刻度2715天，在K频。（2）我们分析了长期的BVRJK光曲线并获得了准周期性： 天， 天，和 年份。（3）多波段光曲线显示时间延迟：=天，=天，=天，和=天。（4）之间的关系和显示出很强的相关性，这是典型的RWB行为；当光源变亮时，光谱指数变红。