Peculiar novae with red K-M spectra in outbursts
E.A. Barsukova, N.V. Borisov (Special Astrophysical Observatory,
Russian Academy of Sciences);
V.P. Goranskij, N.V. Metlova, S.Yu. Shugarov (Sternberg Astronomical
Institute, Moscow University)
Report to the conference VAC-2004 "Horizons of the Universe" held
in Moscow on June 3-10, 2004.
Research was supported by grant No. 03-02-16133 of the Russian Foundation
for Basic Research.
Peculiar novae having red K-M spectra in outbursts do not pass through
nebular stage typical for classic novae and present themselves as a new
class of astrophysical objects and variable stars. Using Munari et al.
(AIP Conf. Proc. V.637, 52, 2002) terminology these are "Stars
Erupting into Cool Supergiants" (SECS).
There are three objects, V4332 Sgr and V838 Mon in our Galaxy, and V1006/7
in Andromeda galaxy, that are investigated enough well to refer them to this
new class. But the nature of these stars is not clear yet.
Images of the peculiar novae. Left: the peculiar nova V1006/7
in Andromeda galaxy in the maximum of its brightness
(Munari et al., 2003).
Right up:the pevuliar nova V838 Mon before the outburst (DSS, R).
Right bottom: the peculiar nova V4332 Sgr after the outburst
(1-m Zeiss SAO RAN, R)
Coordinates for three known peculiar novae
||+41o 12' 56".9
||07 04 04.85
||-03 50 51.1
||18 50 36.73
||-21 23 28.9
V1006/7 M31 = RV = McD 88 No.1. History of investigation.
The nova reached the brightness of B = 17m.5, V = 15m.5
(B-V = 1m.89+/-0.24) in the outburst (A.S.Sharov, Astronomy Letters
v.19, 335, 1993).
In the previous Sharov's paper, some more outburst of this star in 1968 was reported
(SvAL v.16, 855,1990), but later in the paper of 1993 it was disproved.
In that way, the event in 1988 is only reliable outburst
of this star that was registered in 1100 negatives of Sternberg Astronomical
Institute collection in the time range between 1967 and 1992.
In the spectrum of nova obtained by Rich et al.ApJ V.341, L51, 1989),
BaII, CaI and FeI lines predominate on the background of red continuum,
the line of Li at 6708A is seen, too.
Photometry and spectroscopy of V838 Mon
Nova V838 Mon was discovered by N.J. Brown in January 6, 2002.
It is the most studied object of new class. The pre-maximum stage
lasted to February 2, 2002. Maximum of brightness was reached
in February 6, 2002 in the peak of the outburst that resembled
an outgoing shock wave into a star surface.
A second local maximum was observed in 32 days after main maximum.
Light curves of V838 Mon before 2002, in the outburst and after
the outburst in B and red RC bands.
See also an UBVR collection
of observations, including light curves and color indices according to
Nova shows different behaviour in the filters of system RJ
by Johnson and RC by Cousins.
Spectral observations of V838 Mon in the outburst
showed that the star had normal solar like abundance of elements,
and hydrogen rich envelope. Strong line of Li 6708A was idendified.
Intensive absorbtion bands of TiO, VO, AlO and oxides of other
metalls are seen in optical spectra of V838 Mon obtained with the 6-m
telescope in 2004. This is a typical behaviour of oxygen rich cool stars.
These properties distinguish V838 Mon radically from post-AGB flash
stars, V605 Aql, V4334 Sgr and FG Sge, that are on the late stages of
their evolution. These stars are rich of carbon and in the late stages of
outbursts reject carbon dust particles in the atmosphere giving rise
characteristic deeps in the light curves. See e.g.
light curve of "Sakurai object", V4334 Sgr.
Spectrum of V838 Mon in pre-maximum stage obtained with 1-m Zeiss
telescope of SAO RAN and UAGS spectrograph. It reminds a K0 type
red giant spectrum having the absorption lines strengthened by
Spectral changes in the region of H alpha line during
pre-maximum stage, peak of outburst, and decay. The spectra are
taken with 1-m telescope with UAGS spectrograph.
Two components of the system are seen in the spectrum of
V838 Mon after outburst, a hot blue B3V type one having
Balmer absorptions, and a cool 'brown' L type supergiant
having deep absorption molecular bands of metal oxides.
The absorption reaches 100 per cent in some strong bands,
so as the B type star continuum is well seen. The
interstellar reddening of E(B-V)=0m.77 is
taken into account.
V838 Mon before the outburst
was studied on the base of the plate collections of SAI,
Moscow University and of Sonneberg Observatory, Germany,
and digitized sky serveys. After its 2002 outburst,
the star was studied on the base of UBVRI photometry.
We found that the energy distribution before outburst
coincided with a hot B3V star one. But after the
outburst, the spectrum was two-component, and consisted of a
hot B star, and a cool L type supergiant, the radiation
of the last one was concentrated in the long-wavelength
region. It is noted that the contribution of the hot star in
the blue band decreased essentially relative to its
pre-outburst level. There are two alternative explanations
of this phenomenon. The first one suggests that the B type star
participated in the outburst. The second one assumes that
the object of the outburst was another B type star which
mimiced its companion in the pre-outburst spectrum. And
it is absent now in the integral energy distribution.
Due to the contribution of one more B type star the integral
brightness was higher. In any case V838 Mon is a binary system.
Spectral energy distributions of V838 Mon before outburst
(progenitor) and after outburst (remnant). IR waverange
data before outburst are from 2MASS, and those ones after
outburst are from Linch et al., IAUC No.8221, 2003
and Tapia & Persy, IAUC No.8241, 2003.
The energy distribution of progenitor is compared with
B3V type star HD 29763 (the difference of interstellar
reddening between star spectra are taken into account).
Light echo of V838 Mon
Colour image of the light echo around V838 Mon taken with
the 1-m telescope of SAO RAS on December 30, 2003. Note that
the star, V838 Mon is located not in the center of the
round nebula illuminated by the outburst light.
Propagation of the light echo boundary in four directions
versus time. Note that the velocity of the propagation
decreases during the first months of observations, and
the echo edge moves away with different velocities depending
Modelling of light echo..
The light of the outburst peak illuminates in the given time
t for an external observer the particles of the
interstellar medium located along the 3D surface of expanding
ellipsoid, so as the source of the outburst, and the observer
turn up in its focal points, and the sum of the distances between
each particle and focal points is equal to d+ct (where
d is a distance from the observer to the
star). The non-central location of the outburst source relative to
the edge of the nebula may be explained with the assumption
that the boundary of the dence interstellar medium is inclined
to the line of sight (upper Figure). The light propagates
along the line of the intersection between the face-on plane and
the plane boundary of the interstellar medium according to the
simplified formula y(x,t) for the remote observer,
where x is the depth of immersion the outburst source
into interstellar medium (see formula at the bottom of the
Figure). Analysis of this formula shows that the apparent
velocity of the edge propagation is always superluminal, and
approaches to the value of light velocity asymptotically from
upper side. So, we are in a position to determine distance to
V838 Mon with the accuracy improving with the time of observations.
Using the plot in the previous Figure, the distance may revealed
of about 4 Kps. (In the general case, the equations for the
light echo propagation are derived by R.Tylenda, AsAp
V.414, 223, 2004).
Photometry of V4332 Sgr
The outburst of V4332 Sgr has happened in 1994, and observed
only at its late stages because the object was located
in the direction of the Sun. The detailed spectroscopic
and photometric study of the star in outburst was published
by Martini et al. (ApJ V.118, 1034, 1999).
During the light decay the spectrum varied from K3-4III-I to
M3III-I. In the quiet state after outburst, the emission lines
H, MgI, FeI, FeII, [OI] were seen in the spectrum.
This property distinguishes the star from V838 Mon which
doesn't show the emissions in the quiet state. The cool
star is presented in the red and IR spectrum by the molecular
bands TiO and VO. The spectra of V4332 Sgr taken in 2003 by
Banergee and Ashok (ApJ V.604, L57, 2004) look
unusually with bright emissions NaI, K I, and RbI, and
molecular bands of TiO in emission.
Historical light curves of V4332 Sgr in BVRI bands.
See modern data
The duplicity of V4332 Sgr is not yet discovered. We have
studied this star using digitized sky serveys. We found
also six plates with the pre-outburst images of V4332 Sgr
taken in 1977-1986 with the 50-cm meniscus telescope AZT-5
in the B and V bands. Comparing the measures of historic
negatives, and modern CCD observations, we found that the
brightness of V4332 Sgr fell down by 0m.6
relative its pre-outburst level, like this one of V838 Mon.
So, three known peculiar novae show the essential similarities
in the photometric and spectroscopic behaviour to declare
the discovery of a new class of astrophysical objects and
variable stars. At the same time two galactic novae of this
class display the spectral difference in its quiet states.