NGC-4151 - INFRARED VARIABILITY

The results of an almost 12-year-long JHKL photometry of a 12 '' regio n in the Seyfert 1s galaxy NGC 4151 are presented. An analysis of the observations shows that the infrared brightness of the galaxy consider ably increased from 1985 through 1996 (by similar to 0(m).9 at lambda 1.25 mu m, by similar to 1(m) at lambda 1.65 mu m, by similar to 1(m). 1 at lambda 2.2 mu m, and by lambda similar to 1(m).33 at 3.5 mu m). T he brightening was accompanied by its reddening. We could not determin e how the JHKL brightness rose-abruptly or smoothly-from our observati ons, because there were no observations from 1989 to 1993. In the two- color H-K, J-H and K-L, H-K diagrams, our photometric JHKL data cluste r around the infrared color curve of a source with a power-law spectra l energy distribution. A search for periodic JHKL light variations in NGC 4151 points to the possible of several periods in the observed inf rared light and color variations of the galaxy. The period of 43.0 day s seems most plausible.