Tracing accretion variability of high-mass YSOs via light echoes
  There is growing evidence for disk-mediated accretion being the dominant mode
of star formation across nearly the whole stellar mass spectrum. The stochastic
nature of this process has been realized which implies an inherent source
variability. It can be traced more easily for low-mass YSOs (LMYSOs) since
high-mass YSOs (HMYSOs) are still embedded even when reaching the ZAMS. While
variable reflection nebulae around LMYSOs were among the earliest signs of star
formation, little is known on the variability of scattered light from embedded
clusters, the birthplaces of HMYSOs. Since the few most massive stars dominate
this emission, their variability is literally reflected in scattered light.
Moreover, because of their high luminosity, for a given ambient dust density
and source distance, the associated nebulosities are much larger than those of
LMYSOs. In this case, the light travel time becomes substantial. So the
apparent brightness distribution constitutes a light echo, shaped by both the
HMYSO variability history and the spatial distribution of the scattering
medium. We report on early results of a NIR variability study of HMYSOs
associated with Class II methanol masers which aims at revealing a possible
correlation between maser flux density and infrared brightness. Additionally,
relevant findings for the eruptive HMYSO S255IR-NIRS3 are presented.
