  ISO-Oph-50 is a young low-mass object in the ~Myr old Ophiuchus star forming
region undergoing dramatic changes in its optical/near/mid-infrared brightness
by 2-4 mag. We present new multi-band photometry and near-infrared spectra,
combined with a synopsis of the existing literature data. Based on the
spectroscopy, the source is confirmed as a mid M dwarf, with evidence for
ongoing accretion. The near-infrared lightcurves show large-scale variations,
with 2-4 mag amplitude in the bands IJHK, with the object generally being bluer
when faint. Near its brightest state, the object shows colour changes
consistent with variable extinction of dAV~7 mag. High-cadence monitoring at
3.6mu reveals quasi-periodic variations with a typical timescale of 1-2 weeks.
The best explanation for these characteristics is a low-mass star seen through
circumstellar matter, whose complex variability is caused by changing
inhomogeneities in the inner parts of the disk. When faint, the direct stellar
emission is blocked; the near-infrared radiation is dominated by scattered
light. When bright, the emission is consistent with a photosphere strongly
reddened by circumstellar dust. Based on the available constraints, the
inhomogeneities have to be located at or beyond ~0.1 AU distance from the star.
If this scenario turns out to be correct, a major portion of the inner disk has
to be clumpy, structured, and/or in turmoil. In its observational
characteristics, this object resembles other types of YSOs with variability
caused in the inner disk. Compared to other objects, however, ISO-Oph-50 is
clearly an extreme case, given the large amplitude of the brightness and colour
changes combined with the erratic behaviour. ISO-Oph-50 has been near its
brightest state since 2013; further monitoring is highly encouraged.
