UBVJHKLMN photometry and optical spectrophotometry of the symbiotic Mira V407 Cygni

The optical and infrared photometric and spectroscopic observations of the symbiotic star V407 Cyg in 1984-1997 are presented. Its cool component is shown to be a Mira variable with a pulsation period P ~ 745d and an amplitude delta K <= 1m. While the pulsation period may be unstable on a short time scale, its mean value given above has not changed appreciably over the last 50 years. It is noted that the intensity of the TiO lambda 6180 and lambda 7100 Angstrom bands and, accordingly, the spectral type of the Mira can be the same for its different (delta V >= 2) brightness. The mean infrared brightness of V407 Cyg increased during our observations, and, simulta- neously, the star became bluer. In 14 years, it brightened in K by >= 0.4m. The pulsations and the trend are attrib- utable to variations in the same parameters of the star: in the luminosity and temperature of the Mira, as well as in the optical depth of the dust envelope. The latter consists of a mixture of fairly large (agr >= 0.08 micron) silicate and graphite grains. Its optical depth at maximum light of the Mira is (J) 0.25. The mass-loss rate over the last decade was ~7x10^7 M_sun yr^-1, which is more than one order of magnitude lower than the expected value for a Mira with such a long pulsation period. The spectrum of V407 Cyg was first obtained in August 1994; it appears as a typical symbiotic spectrum with numerous emission lines against the emission from a red giant. During the outburst, the temperature of the hot component was ~ 6 x 10^4, while its bolometric luminosity did not exceed 1% of the maximum luminosity of the Mira.