Characterisation of an EXor outburst SPICY 97589

TL;DR

This paper characterizes a new EXor-type stellar outburst in 2023, analyzing its accretion rate, stellar parameters, and disk evolution through multi-wavelength spectroscopy.

Contribution

It provides the first detailed characterization of SPICY 97589's 2023 outburst, including stellar parameters and accretion rate measurements, confirming its EXor nature.

Findings

The star is an M3.0 type with 0.29 solar masses.

Accretion rate during outburst is approximately 2.38e-7 solar masses per year.

Outburst driven by influx of material, with spectral features of an EXor source.

Abstract

Stellar outbursts from variable or periodic accretion are thought to be ubiquitous across young stellar populations. However, relatively few outbursting objects have been discovered to date. Here, we present the characterisation of a new EXor-type episodic accretor. We aim to characterise the nature of the 2023 outburst of SPICY 97589/Gaia23bab and characterise the stellar source for the first time, while exploring how an accretion outburst contributes to disk evolution. We employ multi-waveband medium-resolution spectroscopy with UVB-VIS-NIR coverage during the peak of the 2023 outburst and the post-outburst quiescent object. The broad wavelength coverage of the dataset allows for robust measurements of the accretion rate using known line tracers. The addition of quiescent spectra provides a good estimation of stellar parameters of the central star while also informing us on the evolution of the disk during outburst phases. We find the stellar source to be a 3410\,K, M3.0 type star with a luminosity of 0.41 $L_\odot$ and an estimated stellar mass of 0.29 $M_\odot$. We measure the accretion rate of SPICY 97589 to be $\dot M = 2.38\pm0.58\times10^{-7}\,\mathrm{M_\odot yr^{-1}}$. This value is at two orders of magnitude greater than the quiescent accretion rate. Thus, we confirm that the 2023 outburst was driven by an influx of material from the surrounding environment to the central star, an accretion outburst. The spectral fingerprint of emission lines is also characteristic of an outbursting EXor-type source, including variable disk winds.