Sudden decay of V838 Mon

ATel #964; V. Goranskij (SAI, Moscow Univ., Russia)
on 15 Dec 2006; 01:06 UT
Credential Certification: Vitaly Goranskij (goray@sai.msu.ru)

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V838 Mon is a peculiar nova having red K-M spectra in its 2002 outburst. It is a member of a new class of eruptive variables of unknown nature. The star was found to be a spectroscopic binary containing a cool L type supergiant, the remnant of the outburst, and a B3V type companion. The spectrum of companion is predominating in the short-wave photometric bands. Recently I have detected sudden decrease of brightness of V838 Mon in the UBV photometric bands. The CCD UBVRc observations were carried out using 60-cm telescope of SAI Crimean station. The sudden change is seen since 2006 Dec. 2, 23.3 UT with values of B,V,Rc=(17.33,15.75,13.13), and the following observation on 2006 Dec.10, 22.3 UT is U,B,V,Rc=(18.1,17,52,15.76,13.13). The last observation before the change was taken with SAO 1-m telescope on 2006 Oct. 26, U,B,V,Rc=(16.39,16.42,15.36,13.17). No observations are present between these dates, and the duration of the descending branch is yet unknown. The amplitude of this decay is the largest in the U and B bands, where the contribution of B3V companion is large, and no decay is seen in Rc. So, the eclipse of B3V companion by L supergiant is a possible explanation.

Java generated light curves of V838 Mon