Title: Investigating the past history of EXors: the cases of V1118 Ori, V1143 Ori, and NY Ori,
Abstract: EXor objects are young variables that show episodic variations of brightness
commonly associated to enhanced accretion outbursts. With the aim of
investigating the long-term photometric behaviour of a few EXor sources, we
present here data from the archival plates of the Asiago Observatory, showing
the Orion field where the three EXors V1118, V1143, and NY are located. A total
of 484 plates were investigated, providing a total of more than 1000 magnitudes
for the three stars, which cover a period of about 35 yrs between 1959 to 1993.
We then compared our data with literature data. Apart from a newly discovered
flare-up of V1118, we identify the same outbursts already known, but we provide
two added values: (i) a long-term sampling of the quiescence phase; and (ii)
repeated multi-colour observations (BVRI bands). The former allows us to give a
reliable characterisation of the quiescence, which represents a unique
reference for studies that will analyze future outbursts and the physical
changes induced by these events. The latter is useful for confirming whether
the intermittent increases of brightness are accretion-driven (as in the case
of V1118), or extinction-driven (as in the case of V1143). Accordingly, doubts
arise about the V1143 classification as a pure EXor object. Finally, although
our plates do not separate NY Ori and the star very close to it, they indicate
that this EXor did not undergo any major outbursts during our 40 yrs of
monitoring.