An infrared view of the EXor variables: on the case of V1118 ORI

TL;DR

This study compiles 30 years of IR data on EXor variables, especially V1118 Ori, revealing that brighter phases are bluer and supporting disk accretion models, with new IR spectra and polarimetry providing insights into the star's activity and magnetic properties.

Contribution

It provides a comprehensive IR catalog of EXor variables and presents new IR spectra and polarimetry for V1118 Ori, enhancing understanding of their accretion processes and magnetic features.

Findings

Brighter states tend to be bluer in IR.

Disk accretion via viscous friction aligns with observations.

V1118 Ori's spectrum shows no emission lines a year after outburst.

Abstract

We investigate the relationship between the IR observed properties of the EXor variables and the mechanisms active during their evolutionary stage. To this aim, we have constructed a catalog of all the IR (1-100 micron) photometric and spectroscopic observations appearing during the last 30 years in the literature. New results of our monitoring program based on near- and mid-IR photometry and near-IR spectroscopy and polarimetry of one object (V1118 Ori) are presented, complementing those given in a previous paper and related to a different activity period. Our catalog indicates how the database accumulated so far is inadequate for any statistical study of the EXor events. Nevertheless, all the observational evidence can be interpreted into a coherent scheme. The sources that present the largest brightness variations tend to become bluer while brightening. The scenario of disk accretion based on viscous friction between particles agrees with the observations. The new results on V1118 Ori confirm such a general view. The striking novelty is represented by a near-IR spectrum of V1118 Ori taken 1 yr after the last monitored outburst: any emission line previously detected has now totally disappeared at our sensitivity. For the same source, mid-IR photometry is provided here for the first time and allows us to construct a meaningful SED. The first polarimetric data show that V1118 Ori is intrinsically polarized and its spotted, magnetized surface becomes recognizable during the less active phases.