PV Cep: an infrared dramatic declining in 80 days

ATel #1607; A. A. Arkharov (1), V. M. Larionov (2), R. Leoni (3), N. Napoleone (3), A. Di Paola (3), T. Giannini (3), D. Lorenzetti (3) - (1) Central Astronomical Observatory of Pulkovo, Pulkovskoe shosse 65, 196140 St. Petersburg, Russia, (2) Astronomical Institute of St. Petersburg University, Russia, (3) INAF - Osservatorio Astronomico di Roma, via Frascati 33, I-00040 Monte Porzio, Italy
on 8 Jul 2008; 10:16 UT
Credential Certification: Dario Lorenzetti (dloren@mporzio.astro.it)

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From the Campo Imperatore (Italy) AZT24 1m IR telescope, we have observed the variable pre-main sequence (PMS) star PV Cep (Cohen, Kuhi & Harlan 1977 ApJ 215, L127; Gyulbudaghian et al. 1977 SvAL 3, 84), to undergo a dramatic declining lasting 80 days (from March 31th , 2008 MJD = 54556, to June 18th 2008 MJD = 54635). We have monitored the object both photometrically and spectroscopically in the near-IR (0.8 - 2.5 ìm) from its maximum light (J ~ 9.9 mag) to its historical minimum (J ~ 12.4 mag). The observed portion of the light curve in the JHK bands is given in Figure 1 (see http://sirio.rm.astro.it/cimperatore/en/events/PVCep.html ).

During such fading, we have taken also three near-IR low resolution (R~250) spectra on April 12th (near the maximum), June 9th and June 18th (near the minimum): they are depicted in Figure 2 (see http://sirio.rm.astro.it/cimperatore/en/events/PVCep.html ). The first one presents strong hydrogen recombination lines of the Paschen and Brackett series, some ionic features, and also emission in the overtone bands of CO (v=2-0, v=3-1). While the continuum declines also line emission fades (HI by about a factor of 2, and CO by more than 1 order of magnitude). Since the equivalent widths vary significantly, as well, spectroscopical variations do not merely follow the continuum ones.

This object belongs to the class of the low mass PMS EXor eruptive variables (ATEL #1256) that are the targets of a monitoring program we are performing since few years (Lorenzetti et al. 2006, 2007). Data presented here sample the coming back to a quiescent phase after a recent outburst and the same behaviour of another object (V1118 Ori) of the same class has been already reported (ATEL #619, #1015). These manifestations are fully compatible with disk accretion events. The matter accumulated in the disk episodically falls onto the star, provoking, in turn, intermittent outbursts; during the outburst phase: (i) the luminosity increases; (ii) the UV radiation produced at the accretion shock heats the inner regions of the disk itself which emits (CO and other ions) more strongly; (iii) to self-regulate the momentum, an intermittent mass ejection from the star occurs accordingly, with a consequent increase of the line emission (HI recombination) that likely originates in the wind. The timescale of the monitored event (80 days) appears shorter than the typical declining times (months to year) of the other EXor’s.