Photometric and spectroscopic study of the EXor-like eruptive young star Gaia19fct

TL;DR

Gaia19fct is an eruptive young star with multiple brightening events, displaying complex spectral features and behaviors that suggest it shares more characteristics with EXors than FUors, providing insights into its physical properties and eruption mechanisms.

Contribution

This study provides detailed photometric and spectroscopic analysis of Gaia19fct, revealing its unique spectral features and variability, and clarifies its classification among eruptive young stars.

Findings

Multiple brightening events since 2015.

Gray color evolution indicating non-extinction triggers.

Spectral evidence of a Keplerian disk and mixed emission/absorption CO features.

Abstract

Gaia19fct is one of the Gaia-alerted eruptive young stars that has undergone several brightening events. We conducted monitoring observations using multi-filter optical and near-infrared photometry, as well as near-infrared spectroscopy, to understand the physical properties of Gaia19fct and investigate whether it fits into the historically defined two classes. We present the analyses of light curves, color variations, spectral lines, and CO modeling. The light curves show at least five brightening events since 2015, and the multi-filter color evolutions are mostly gray. The gray evolution indicates that bursts are triggered by mechanisms other than extinction. Our near-infrared spectra exhibit both absorption and emission lines and show time-variability throughout our observations. We found lower rotational velocity and lower temperature from the near-infrared atomic absorption lines than from the optical lines, suggesting that Gaia19fct has a Keplerian rotating disk. The CO overtone features show a superposition of absorption and emission components, which is unlike other young stellar objects. We modeled the CO lines, and the result suggests that the emission and absorption components are formed in different regions. We found that although Gaia19fct exhibits characteristics of both types of eruptive young stars, FU Orionis-type objects (FUors) and EX Lupi-type objects (EXors), it shows more similarity with EXors in general.