A long-lasting quiescence phase of the eruptive variable V1118 Ori

TL;DR

This study documents the longest observed quiescence phase of the eruptive star V1118 Ori, providing detailed near-infrared data and analyzing physical parameters to understand its accretion behavior during low activity.

Contribution

It offers the first comprehensive long-term quiescence data for V1118 Ori, establishing baseline parameters and examining emission line behavior across optical and infrared wavelengths.

Findings

Derived a low mass accretion rate of 1-3 x 10^-9 M_sun/yr during quiescence.

Confirmed V1118 Ori as a low-extinction T Tauri star with L_bol ≈ 2.1 L_sun.

Identified anti-correlation between emission line equivalent width and continuum in optical, supporting accretion-driven variability.

Abstract

V1118 Ori is an eruptive variable belonging to the EXor class of Pre-Main Sequence stars whose episodic outbursts are attributed to disk accretion events. Since 2006, V1118 Ori is in the longest quiescence stage ever observed between two subsequent outbursts of its recent history. We present near-infrared photometry of V1118 Ori carried out during the last eight years, along with a complete spectroscopic coverage from 0.35 to 2.5 um. A longterm sampling of V1118 Ori in quiescence has never been done, hence we can benefit from the current circumstance to determine the lowest values (i.e. the zeroes) of the parameters to be used as a reference for evaluating the physical changes typical of more active phases. A quiescence mass accretion rate between 1--3 $\times$ 10$^{-9}$ M$_{\sun}$ yr$^{-1}$ can be derived and the difference with previous determinations is discussed. From line emission and IR colors analysis a visual extinction of 1-2 mag is consistently derived, confirming that V1118 Ori (at least in quiescence) is a low-extinction T Tauri star with a bolometric luminosity of about 2.1 L$_{\sun}$. An anti-correlation exists between the equivalent width of the emission lines and the underlying continuum. We searched the literature for evaluating whether or not such a behaviour is a common feature of the whole class. The anti-correlation is clearly recognizable for all the available EXors in the optical range (H$\beta$ and H$\alpha$ lines), while it is not as much evident in the infrared (Pa$\beta$ and Br$\gamma$ lines). The observed anti-correlation supports the accretion-driven mechanism as the most likely to account for continuum variations.