V838 Mon: Radical spectral changes at the short wavelengths
V.P. Goranskij (SAI, Moscow Univ.) and E.A. Barsukova (Special
Astrophysical Observatory, Russia)
Published in Astronomer's Telegram No. 1821.
We continue multicolor photometric CCD UBVRI monitoring of
the peculiar red nova V838 Mon using CCD
photometer and SAO RAS 1-m reflector.
New observations were obtained in two nights in
October 2008. We noted strong changes in the U and B bands happened
between 2008 April and October. The star became invisible in U band
frames. In two nights we have accumulated 6000 s exposures to get
measurable image of the star. The accuracy we have got was 0.2 mag.
The accuracy of magnitudes in other filters was 0.02 mag. The current
magnitudes (U,B,V,Rc,Ic) comparing with the April 2008 data are
2008 Apr 10.75 UT (18.50,17.72,15.76,12.94,10.22);
2008 Oct 27.05 UT (20.75,18.48,15.79,12.90,10.17);
2008 Oct 28.03 UT (21.06,18.49,15.78,12.92,10.17).
In such a way the nova declined by 2.4 mag in the U band and by
0.76 mag in the B band. Changes in other filters are small.
To understand these changes, one should take into account that before
the explosion in 2002, V838 Mon was a system containing two B3V type
stars, and brighter companion exploded. The remnant of the explosion
was an expanding very cool star, a possible L type supergiant.
The secondary B3V star remained in the spectrum of the system.
Since 2004 till 2006 the forbidden FeII emissions strengthened in
the short wavelength spectrum. This was possibly due to an approach
of the ejecta to B3V companion (ATEL #803). In Dec 2006,
B3V type star disappeared from the spectral energy distribution
(ATEL #964) and reappeared in 70 days
(Munari et al., 2007). At the same time, the emission line spectrum
remained very strong. In the season of 2007-2008, B3V companion
was captured by expanding remnant, but its variable radiation
leaked through the cloudy structure of the remnant's envelope.
This radiation of B star excited weak [FeII] lines.
The radius of cool star was estimated as 30.000 solar radii at the moment
of the capture
(Goranskij et al., 2008).
Evidently, the hot B3V companion has entered now in dense parts
of the cool star's envelope, and its radiation does not come out.
The engulf of the hot star assumed by Bond (ATEL #966) has happened
Additionally, the radiation of excited gas being strong in this
spectral range disappeared. So the contribution of the cool remnant
stays on dominanting. Our current photometry agrees with the Planck
energy distribution of a single body with the temperature of
This investigation is supported
by Russian Foundation for Basic Rrsearch Grant No.07-02-00630.
Fig. 1. V838 Mon in the U band frame with 6000 s accumulated
exposure (on the left). V band frame is on the right.
Fig. 1. Spectral energy distributions of V838 Mon before and
after the outburst. Five-digit numbers are Julian Dates - 2400000.
View of current
UBVRcRjIcIj light curves of V838 Mon. Java compatible brouser is
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