Infrared photometry of Sakurai's object (V4334 Sgr) in 1996-1999

The infrared photometric observations of V4334 Sgr in 1996-1999 are present ed. Together with optical data, they have allowed us to accurately estimate the bolometric flux from this star and to investigate the structure of its dust envelope over the above period. The star is shown to have passed thro ugh four well-defined stages in these four years as it moved backward along the post-AGE track, and it now appears to have started moving forward afte r a halt. At the first stage (1996), there was no dust in the star's envelo pe. Its visual brightness slightly increased, and it reddened in the entire observed spectral range. The bolometric flux also gradually rose. At the s econd stage (1997), an optically thick dust envelope condensed around the s tar, which, however, essentially did not manifest itself at optical wavelen gths. The bolometric flux continued to rise through an increase in the star 's infrared brightness alone; the rate of its rise also increased. At the t hird stage (1998-March 1999), V4334 Sgr entered the R CrB phase. First two shallow minima and then two deep minima were observed at optical wavelength s. The star appreciably reddened during the deep minima. The bolometric flu x ceased to rise and began to gradually fall in the second half of 1998. At the fourth stage (since March 1999 up until now), V4334 Sgr has been at a protracted deep minimum, which is atypical of the R CrB stars. The bolometr ic flux between March and October underwent no significant variations. We d escribe the structure of the dust envelope around V4334 Sgr since its forma tion. From June 1997 until July 1998, the optical depth of the dust shell, its inner and outer radii, and its mass increased by factors of similar to 2.2, similar to 2.0, 2.3, and similar to 10, respectively. In July 1998, ta u(V) approximate to 2.3, R-d,R-in = 7.4 x 10(14) cm, R-d,R-in/R-d,R- out ap proximate to 0 7 (R-d,R- in/R* approximate to 47), and M-dust approximate t o 1 6 x 10(-7) Mg. (C) 2000 MAIK "Nauka/Interperiodica ".