Highly variable young massive stars in ATLASGAL clumps
  High-amplitude variability in Young Stellar Objects (YSOs) is usually
associated with episodic accretion events. It has not been observed so far in
massive YSOs. Here, the high-amplitude variable star sample of
ContrerasPe\~{n}a et al.(2016) has been used to search for
highly-variable($\Delta$K$\ge$1\,mag) sources coinciding with dense clumps
mapped using the 850\mum continuum emission by the ATLASGAL survey. 18 variable
sources are centred on the sub-mm clump peaks, and coincide ($<$1") with a
24$\mu$m point or compact ($<$10") source. 13 of these 18 sources can be fit by
YSO models. The 13 variable YSOs(VYSO) have luminosities of $\sim$10$^3$
L$_{\odot}$, an average mass of 8 M$_{\odot}$ and a range of ages up to 10$^6$
yr. 11 of these 13 VYSOs are located in the midst of infrared dark clouds. 9 of
the 13 sources have $\Delta$K$>$2 mag, significantly higher compared to the
mean variability of the entire VVV sample. The light curves of these objects
sampled between 2010-2015 display rising, declining, or quasi-periodic
behaviour but no clear periodicity. Light-curve analysis using Plavchan method
show that the most prominent phased signals have periods of a few hundred days.
The nature and time-scale of variations found in 6.7 Ghz methanol maser
emission (MME) in massive stars are similar to that of the VYSO light curves.
We argue that the origin of the observed variability is episodic accretion. We
suggest that the timescale of a few hundred days may represent the frequency at
which a spiralling disk feeds dense gas to the young massive star.
