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V838 Mon: hot component still in deep eclipse

ATEL # 2211; I.Kolka (Tartu Obs.), T.Liimets (NOT, La Palma & Tartu Obs.), E.Kankare, T.Pursimo (NOT, La Palma), J.Datson (NOT, La Palma & Tuorla Obs.)
on 24 Sep 2009; 12:55 UT
Password Certification: Indrek Kolka (

Subjects: Optical, Binaries, Variables, Stars

We report on brightness measurements of the peculiar binary V838 Mon in the B,V,Rc bands in 2009. We have used the ALFOSC and MOSCA cameras at the Nordic Optical Telescope on La Palma. The B magnitudes listed below indicate that the hot B3V component of the binary is still in the deep eclipse which was first reported by Goranskij in ATel #1821. However, one can notice the trend of a mild growth of brightness during the reported time interval:

                           B               V                 Rc   Feb 12.13 UT (ALFOSC) 18.60(+/-0.04) 15.540(+/-0.014) 13.124(+/-0.013)   Mar 20.95 UT (MOSCA)  18.47(+/-0.03) 15.605(+/-0.004)   Apr 16.90 UT (ALFOSC) 18.36(+/-0.07) 15.413(+/-0.011) 13.009(+/-0.005)   Apr 19.89 UT (MOSCA)  18.11(+/-0.13) 15.444(+/-0.050) 12.961(+/-0.010)   Sep 14.20 UT (ALFOSC) 18.32(+/-0.04) 15.382(+/-0.013) 13.015(+/-0.012)   

The current state of low brightness in the blue spectral region is different from the analogous event near the end of 2006 (Munari et al. 2007, A&A, 474, 585) when the duration of the ~1.15 mag dip in the B-band light curve was about 70 days. The ingress into the present eclipse was observable in the season 2007/2008 (Goranskij et al. 2008, arXiv:0810.1887), and the currently continuing lowest brightness level was measured already in October 2008 (ATel #1821). The present situation can be interpreted as a real eclipse of the B3V star by the large disk of the cool primary component (L-type supergiant). In this sense, V838 Mon behaves as a VV Cep type binary. However, the estimates on the distance between the components go up to 150 AU (Goranskij et al. 2008). On the other hand, measurements of spectral lines observed during the outburst period of V838 Mon in 2002 suggested a distance not larger than 10 AU (Kolka and Kipper 2007, ASP Conf. Ser., 363, 235), which seems more concordant with the eclipse scenario. Consequently, we suggest to reconsider the post-outburst behaviour of V838 Mon in the framework of an eclipsing binary with modest separation of the components. Our attempt is in progress at Tartu Observatory using the local spectroscopic and photometric archives plus other publicly available databases.

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