A photometric and spectroscopic study of the Herbig Ae/Be star XY Per

The UBVR photometry of XY Per in 1985–1998 is presented. At this epoch, XY Per exhibited variability with an amplitude of ≈1m in V. The photometric variability of XY Per can be divided into three components: (1) smooth year-to-year variations in mean brightness; (2) quasi-periodic variations with a characteristic time scale of 20–40 days and an amplitude of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $$0\mathop .\limits^m 3$$ \end{document}; and (3) Algol-like minima with a duration of 15–20 days and an amplitude of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $$0\mathop .\limits^m $$ \end{document}. The CLEAN algorithm is used to refine the quasi-period of light variations in the interval 1988–1995, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $$P = 22\mathop .\limits^d 7252$$ \end{document}. The observed variability is assumed to be produced by two mechanisms: circumstellar absorption and nonstationary accretion. An ultraviolet excess was observed in the stellar radiation during the local minimum of 1991, which was associated with an eclipse of the star by a circumstellar formation. The probable reason why it emerged is that part of the eclipsing circumstellar formation fell into the accretion zone. A high-esolution spectrum in the wavelength range 3600–6700 Å contains both photospheric lines and circumstellar shell lines. The shell line profiles suggest mass accretion onto the star at a velocity of 90–140 km s−1. Of the Balmer lines, only Hα is in emission. Its equivalent width is E(Eλ). The strongest Fe II lines, as well as Mg II 4481.33 Å and He I 5875.65 Å, have an emission component at the line center. The presence of emission components in lines with different excitation potentials suggests the presence of a hot gas shell around the star, which is heated very nonuniformly.