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Eruptive variables are young stars that show episodic variations ofbrightness: EXors/FUors variations are commonly associated with enhancedaccretion outbursts occurring at intermittent cadence of months/years (EXors)and decades/centuries (FUors). Variations that can be ascribed to a variableextinction along their line of sight are instead classified as UXors. We aim atinvestigating the long-term photometric behaviour of three sources classifiedas eruptive variables. We present data from the archival plates of the AsiagoObservatory relative to the fields where the targets are located. For the sakeof completeness we have also analysed the Harvard plates of the same regionsthat cover a much longer historical period, albeit at a lower sensitivity,however we are only able to provide upper limits. A total of 273 Asiago plateswere investigated, providing a total of more than 200 magnitudes for the threestars, which cover a period of about 34 yr between 1958 and 1991. We havecompared our data with more recently collected literature data. Our platesanalysis of V2492 Cyg provides historical upper limits that seem not to becompatible with the level of the activity monitored during the last decade.Therefore, recently observed accretion phenomena could be associated with theoutbursting episodes, more than repetitive obscuration. While a pure extinctiondoes not seem the only mechanism responsible for the ASASSN-15qi fluctuations,it can account quite reasonably for the recent V350 Cep variations.

Towards a better classification of unclear eruptive variables: the cases of V2492 Cyg, V350 Cep, and ASASSN-15qi