engleski

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

Context. Eruptive variables are young stars that show episodic variations of brightness: EXors/FUors variations are commonly associated with enhanced accretion outbursts occurring at intermittent cadence of months/years (EXors) and decades/centuries (FUors). Variations that can be ascribed to a variable extinction along their line of sight are instead classified as UXors. Aims. We aim at investigating the long- term photometric behaviour of three sources classified as eruptive variables. We present here data from the archival plates of the Asiago Observatory relative to the fields where the targets are located. For the sake of completeness we have also analyzed the Harvard plates of the same regions that cover a much longer historical period, albeit at a lower sensitivity, so that we are able to provide just upper limits. Methods. A total of 273 Asiago plates were investigated, providing a total of more than 200 magnitudes for the three stars, which cover a period of about 34 yrs between 1958 to 1991. We have compared our data with literature data more recently collected. Results. Our plates analysis of V2492 Cyg provides historical upper limits that seem not compatible with the level of the activity monitored during the last decade. Hence, accretion phenomena recently appeared could be associated with the outbursting episodes, more than repetitive obscurations. While a pure extinction does not seem the only mechanism responsible for the ASASSN-15qi fluctuations, it can account quite reasonably for the recent V350 Cep variations.

Stars: pre-main sequence – Stars: variables – Astronomical Data Bases: catalogues – Stars: individual: V2492 Cyg – Stars: individual: V350 Cep – Stars: individual: ASASSN-15qi

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