Abstract
We present the results of photometric, polarimetric, and spectroscopic observations for the young star IRAS 21204+4913, whose visible brightness has increased by \({\approx}5^{\textrm{m}}\) since October 2025. The star’s absorption spectrum in the range \(0.36\textrm{--}0.75\mu\) m resembles the spectra of A–F giants and supergiants, but at the same time there are molecular TiO bands in its spectrum. The brightening of the star was accompanied by an increase in the degree of polarization of its radiation (to \({\approx}16\%\) in the \(I\) band), probably due to its scattering by dust in an expanding circumstellar shell. The P Cyg H \(\alpha\) line profile implies a dusty wind velocity of \({\approx}300\) km s \({}^{-1}\) . We believe that the outburst of IRAS 21204+4913 is caused by an increase in the accretion rate of protoplanetary disk matter onto the young star with a mass \({\lesssim}0.5\) to \({\gtrsim}3\times 10^{-5}\) \(M_{\odot}\) yr \({}^{-1}\) . At the same time, a number of peculiar features have been detected in IRAS 21204+4913: the dependence of the width and radial velocity of absorption lines on the excitation potential, the emission in the TiO molecular bands, and the outburst with a comparable amplitude occurred in 1948. Several T Tauri stars and a group of Herbig–Haro objects have been found in the vicinity of the star.
