EXORCISM: A Spectroscopic Survey of Young Eruptive Variables (EXor and Candidates)

Abstract

We present an optical/near-IR survey of 11 variable young stars (EXors and EXor candidates) aimed at deriving and monitoring their accretion properties. About 30 optical and near-infrared spectra ( R ∼ 1500 – 2000 ) were collected between 2014 and 2019 with the Large Binocular Telescope (LBT). From the spectral analysis we have derived the accretion luminosity (L acc ) and mass accretion rate ( M ̇ acc ), the visual extinction (A V), the temperature and density of the permitted line formation region (T, n H), and the signature of the outflowing matter. Two sources (ASASSN-13db and iPTF15afq) have been observed in outburst and quiescence, three during a high level of brightness (XZ Tau, PV Cep, and NY Ori), and the others in quiescence. These latter have L acc and M ̇ acc in line with the values measured in classical T Tauri stars of similar mass. All sources observed more than once present L acc and M ̇ acc variability. The most extreme case is ASASSN-13db, for which M ̇ acc decreases by two orders of magnitude from the outburst peak in 2015 to quiescence in 2017. Also, in NY Ori L acc decreases by a factor 25 in one year. In 80% of the sample we detect the [O i] 6300 Å line, a tracer of mass loss. From the variability of the Hα/[O i] 6300 Å ratio, we conclude that mass accretion variations are larger than mass loss variations. From the analysis of the H i recombination lines, a correlation is suggested between the density of the line formation region, and the level of accretion activity of the source.

Photometric and Spectroscopic Study of the EXor-like Eruptive Young Star Gaia19fct

“…The EW of observed spectral lines varies depending on the observation epoch. These spectral line variations are consistent with previous studies (Hillenbrand 2019;Giannini et al 2022), which show different line profiles depending on the brightness of Gaia19fct.…”

“…Gaia19fct has been studied in several works (Miller et al 2015;Hillenbrand 2019;Giannini et al 2022) after its discovery in 2015 (Miller et al 2015). Since 2015, at least five burst events have occurred, and each of these events shows a different amplitude, duration, and speed of brightness variation (Δ mag/Δt; Section 4.3.1), indicating that, similar to the classical EXor V1118 Ori (Giannini et al 2020), these bursts are not the periodic repetition of the same event.…”

“…The brightening in 2019 (ΔG > 4 mag) was reported by the Gaia Photometric Science Alerts Program on 2019 November 14. Giannini et al (2022) presented optical and NIR spectra of Gaia19fct. The quiescent spectrum is dominated by emission lines, while the outburst spectrum is dominated by absorption lines (Hillenbrand 2019;Giannini et al 2022).…”

“…Giannini et al (2022) presented optical and NIR spectra of Gaia19fct. The quiescent spectrum is dominated by emission lines, while the outburst spectrum is dominated by absorption lines (Hillenbrand 2019;Giannini et al 2022). The overall amplitudes, timescales of brightness events, and spectroscopic properties of Gaia19fct are more similar to EXors.…”

Diagnosing FU Ori-like Sources: The Parameter Space of Viscously Heated Disks in the Optical and Near-infrared

“…Our model does not include CO overtone emission, common to smaller EX Lup-type outbursts (e.g., Lorenzetti et al 2009;Aspin et al 2010;Kóspál et al 2011;Giannini et al 2022) and other accretion disks (e.g., Najita et al 1996;Lee et al 2016). This emission is likely generated in a heated disk surface, though a wind origin is possible (see Pontoppidan et al 2011 for an analysis of CO fundamental bands), and requires a more sophisticated approach that includes chemistry to incorporate into our synthetic spectra.…”