The Spectroscopic Variations of the FU Orionis Object V960 Mon

Abstract

We present the results of the spectroscopic monitoring of the FU Orionis type star V960 Mon. Spectroscopic variations of an FU Orionis type star will provide valuable information of its physical nature and the mechanism of the outburst. We conducted medium-resolution ( R  ∼ 10000) spectroscopic observations of V960 Mon with the 2 m Nayuta telescope at the Nishi-Harima Astronomical Observatory, from 2015 January to 2017 January, for 53 nights in total. We focused on H α line and nearby atomic lines, and we detected the strength variations in both absorption and emission lines. The observed variation in the equivalent width of the absorption lines corresponds to a decrease in effective temperature and increase in surface gravity. These variations were likely to originate from the luminosity fading of the accretion disk due to the decrease in mass accretion rate.