Investigating the past history of EXors: the cases of V1118 Orionis, V1143 Orionis, and NY Orionis^⋆

¹ Physics Department, University of Rijeka, Radmile Matejčić, 51000 Rijeka, Croatia
² INAF–Osservatorio Astronomico di Padova, via dell’Osservatorio 8, 36012 Asiago (VI), Italy
³ INAF–Osservatorio Astronomico di Roma, via Frascati 33, 00078 Monte Porzio Catone, Italy
e-mail: antoniucci@oa-roma.inaf.it
⁴ INAF–Istituto di Astrofisica e Planetologia Spaziali, via Fosso del Cavaliere 100, 00133 Roma, Italy

Received: 21 December 2016
Accepted: 23 February 2017

Abstract

Context. EXor objects are young variables that show episodic variations of brightness commonly associated to enhanced accretion outbursts.

Aims. 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.

Methods. A total of 484 plates were investigated, providing a total of more than 1000 mag for the three stars, which cover a period of about 35 yr between 1959 to 1993. We then compared our data with literature data.

Results. 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 yr of monitoring.