The Spectroscopic Variations of the FU Orionis Object V960 Mon

TL;DR

This study monitors spectroscopic changes in the FU Orionis star V960 Mon over two years, revealing how its spectral lines vary with luminosity and accretion rate, shedding light on its physical evolution.

Contribution

First detailed spectroscopic monitoring of V960 Mon showing how spectral line variations relate to physical changes during outburst decay.

Findings

Absorption line strength decreased, indicating cooling and increased gravity.

Emission lines varied, reflecting changes in accretion activity.

Luminosity fading linked to decreasing mass accretion rate.

Abstract

We present the results of the spectroscopic monitoring of the FU Orionis type star V960 Mon. Spectroscopic variations of a 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 2m Nayuta telescope at the Nishi-Harima Astronomical Observatory, from 2015 January to 2017 January for 53 nights in total. We focused on H alpha line and nearby atomic lines, and detected the strength variations in both absorption and emission lines. The observed variation in the equivalent width of the absorption lines correspond 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.