Insights gained from the Light Echo of Cepheus A HW2

TL;DR

This study uses light echoes to analyze the variability and environment of the massive young stellar object Cepheus A HW2, revealing new insights into its circumstellar dust and maser activity.

Contribution

First application of light echo analysis for reverberation mapping of a young stellar object environment, extending its light curve into the past.

Findings

Reconstructed mid-IR light curve since 2007.

Identified periodicity similar to maser flares.

Provided information on dust distribution and viewing geometry.

Abstract

Cepheus A HW2 is a well-studied massive young stellar object (MYSO) featuring Class II methanol masers. Recently, certain maser components have been found to flare every five years. This period went undetected in (NEO)WISE photometry due to detector saturation. However, difference imaging revealed a light echo (LE), representing a variability record. Its periodicity is similar to that of the masers. Thereby, the mid-IR light curve since 2007 could be reconstructed. Phase and period maps provide information on the circumstellar dust distribution and viewing geometry. This is the first time an LE has been used for reverberation mapping of a YSO environment and expanding its light curve into the past.