Spectroscopic follow-up of Gaia alerted Young Stellar Object variables: the Large Binocular Telescope view

TL;DR

This study uses optical/near-IR spectra from the Large Binocular Telescope to analyze 16 Gaia-alerted Young Stellar Objects, revealing episodic accretion behaviors and characterizing their stellar and accretion properties during different brightness phases.

Contribution

It provides the first detailed spectroscopic analysis of Gaia-alerted YSOs, linking photometric variability to accretion processes and stellar parameters across different evolutionary stages.

Findings

All sources are accreting YSOs with emission lines indicating accretion and outflows.

Episodic accretion is common, with some sources showing burst-related accretion rates.

One source exhibits exceptionally high accretion luminosity, suggesting diverse accretion behaviors.

Abstract

We analyzed optical/near-IR Large Binocular Telescope spectra of 16 sources alerted by Gaia between 2021 and 2024 due to significant photometric variability. Half of the spectra were taken during quiescence and the rest during a burst or at intermediate brightness. Our analysis of their ten-year light curves and photometric/spectroscopic features provide evidence that all 16 sources are accreting Young Stellar Objects (YSOs). One object, Gaia23bab, is a known EXor source. Other light curves either have peaks over a stable baseline, or significant variability throughout the entire observation period, suggesting multiple contributing processes. All spectra exhibit emission lines from accretion columns, and over half of them show atomic forbidden lines as signatures of outflowing gas. We determined stellar parameters, accretion luminosity (Lacc) and mass accretion rate (Macc) at different brightness phases. Only two sources showed variability primarily due to extinction. During quiescence, our sources exhibit Lacc and Macc values typical of T Tauri and Herbig Ae/Be (HAEBE) sources, supporting the hypothesis that any YSO may undergo episodic accretion. In bursts, the Lacc and Macc of sources with photometric variations exceeding 2 mag follow a shallower relation with stellar luminosity and mass, typical of known EXor sources. This group includes one Class I, one flat-spectrum, and two Class II sources. Notably, the other Class I source, Gaia24beh, shows an Lacc value about ten times higher than typical EXor bursts of the same mass. In the other cases, Lacc and Macc align with variability seen in T Tauri and HAEBE sources.