Infrared photometry of Sakurai’s object (V4334 Sgr) in 2000

The infrared photometric observations of V4334 Sgr in 2000 are presented. They show that a gradual, but nonmonotonic increase in the optical depth of its dust envelope, which was formed early in 1997, had continued until the mid-summer. In July 1999 and July 2000, τ(1.25 µm)≈7.7 and 11.3, respectively. From July through October 2000, the optical depth decreased appreciably. From October 1998 (the first deep minimum of visual brightness) until now, the amplitude of the bolometric-magnitude variations in V4334 Sgr is \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $$ \sim 0^m .5$$ \end{document}. The relation between the bolometric and L magnitudes (mbol, L) can be fitted by a linear function, mbol = 1.25L + 4.04. In the dust-envelope model chosen, the percentage of large (agr=0.2–0.3 µm) dust grains by particle number increased by a factor of ∼4. In the summer of 2000, their fraction by mass was ∼78%, and they mainly contributed to the optical depth of the dust envelope. No appreciable correlation between optical depth and bolometric flux was observed.