# A multi-wavelength study of the young star V1118 Orionis in outburst

## TL;DR

This study monitored the 2005-2006 outburst of young star V1118 Orionis across multiple wavelengths, revealing how accretion processes influence stellar and disk emissions, and providing insights into star-disk interactions during outbursts.

## Contribution

It presents a comprehensive multi-wavelength observational analysis of V1118 Orionis's outburst, highlighting the dynamic interplay between accretion, stellar magnetosphere, and disk emissions.

## Key findings

- Optical flux variations linked to hot spot activity.
- X-ray flux correlated with optical/infrared, indicating accretion influence.
- Mass accretion rate increased from 2.5E-7 to 1E-6 Msun/yr during outburst.

## Abstract

Abriged version for astroph: The young late-type star V1118 Orionis was in outburst from 2005 to 2006. We followed the outburst with optical and near-infrared photometry; the X-ray emission was further probed with observations taken with XMM-Newton and Chandra during and after the outburst. In addition, we obtained mid-infrared photometry and spectroscopy with Spitzer at the peak of the outburst and in the post-outburst phase. The spectral energy distribution of V1118 Ori varied significantly over the course of the outburst. The optical flux showed the largest variations, most likely due to enhanced emission by a hot spot. The latter dominated the optical and near-infrared emission at the peak of the outburst, while the disk emission dominated in the mid-infrared. The X-ray flux correlated with the optical and infrared fluxes, indicating that accretion affected the magnetically active corona and the stellar magnetosphere. The thermal structure of the corona was variable with some indication of a cooling of the coronal temperature in the early phase of the outburst with a gradual return to normal values. Color-color diagrams in the optical and infrared showed variations during the outburst, with no obvious signature of reddening due to circumstellar matter. Using MC realizations of star+disk+hotspot models to fit the SED in ``quiescence'' and at the peak of the outburst, we determined that the mass accretion rate varied from about 2.5E-7 Msun/yr to 1E-6 Msun/yr; in addition the fractional area of the hotspot increased significantly as well. The multi-wavelength study of the V1118 Ori outburst helped us to understand the variations in spectral energy distributions and demonstrated the interplay between the disk and the stellar magnetosphere in a young, strongly accreting star.