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Eruptive star V1180 Cas now in outburst

ATel #5421; S. Antoniucci (INAF - Osservatorio Astronomico di Roma, Monte Porzio, Italy), A. A. Arkharov (Pulkovo Observatory, St. Petersburg Russia), N. Efimova, E. N. Kopatskaya, V. M. Larionov, (Astronomical Institute of St. Petersburg University, Russia; Pulkovo Observatory, Russia), A. Di Paola, T. Giannini, G. Li Causi, D. Lorenzetti, F. Vitali (INAF - Osservatorio Astronomico di Roma, Monte Porzio, Italy)
on 26 Sep 2013; 13:59 UT
Credential Certification: Simone Antoniucci (antoniucci@oa-roma.inaf.it)

Subjects: Infra-Red, Star, Variables, Young Stellar Object, Pre-Main-Sequence Star

Referred to by ATel #: 5427

In the framework of our optical/near-IR EXor monitoring program dubbed EXORCISM (EXOR optiCal Infrared Systematic Monitoring - Antoniucci et al. PPVI), we have been observing since two months the variable star V1180 Cas, associated with the dark cloud Lynds 1340. This source has been originally recognized as a young eruptive object by Kun et al. (2011, ApJ 733, L8), who observed a powerful outburst (5-6 mag in the Ic band) in the period 2005-2008. They also noted that the bright and faint phases had comparable temporal lengths, which is not a typical behavior of EXors, whose light-curves, albeit characterized by repetitive outbursts, present long-lasting (years) periods of quiescence between subsequent short-lasting (months) outbursts.

We provide near-IR photometry we obtained during the last two months, which could help in the interpretation of the nature of V1180 Cas. Magnitudes are summarized in the table below:
JD-2400000.5 J H K
5650615.6413.6912.06
5651014.4312.9011.66
5651114.6813.0811.77
5651515.6513.6511.96
5651715.6813.6512.03
5652013.9212.60...
5653916.2614.0011.53
5654015.9513.7412.00
5655813.6012.2111.13
5655913.6012.2311.14

Typical errors of the near-IR magnitudes are less than 0.04 mag.

Superposed over a certain level of variability, two major outburst events are recognizable: the first (ΔJ ~ 1.5, ΔH ~ 1.0, ΔK ~ 0.5 mag) was on date 56520 (2013, Aug. 16) and lasted less than 20 days; the second and more pronounced (ΔJ ~ 2.4, ΔH ~ 1.7, ΔK ~ 1.0 mag) was firstly detected on MJD 56558 (2013, Sept. 23) and is still ongoing. We also plot the [J-H] vs. [H-K] two-color diagram , for which we take into account also the available 2MASS photometry; we marked with blue and red points the colors of the two brightest and faintest states, respectively. The diagram indicates that V1180 Cas is currently in the highest state of near-IR emission ever detected; also, it appears that pure extinction alone cannot describe the color variations, in agreement with the conclusions of Kun el al. (2011). Hence, scenarios involving variable extinction only (like UXor systems, e.g. Shenavrin et al. 2012, ARep 56, 379S) do not seem appropriate. Assuming accretion-related outbursts, the observed rapid variations appear more compatible with an EXor rather than FUor object.