New clues on the model of YY Her after two seasons

Abstract

During two observational seasons of international campaign of YY Her we secured photometric data which covered the primary as well as the secondary minima and revealed unexpected outburst activity of this system.

Full text

Revista Mexicana de Astronomía y Astrofísica
ISSN: 0185-1101
rmaa@astroscu.unam.mx
Instituto de Astronomía
México
Hric, L.; Dobrotka, A.; imon, V.; Petrík, K.; Niarchos, P.; Velič, Z.; Gazeas, K.; melser, L.; Hájek,
P.; Sobotka, P.; Koss, K.; Brát, L.; Lomoz, F.
New clues on the model of yy her after two seasons
Revista Mexicana de Astronomía y Astrofísica, vol. 20, julio, 2004, p. 222
Instituto de Astronomía
Distrito Federal, México
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IAU Colloquium 194 - Compact Binaries in the Galaxy and Beyond (© Copyright 2004: IA, UNAM)
Editors: G. Tovmassian & E. Sion
RevMexAA (Serie de Conferencias),20, 222–222 (2004)
NEW CLUES ON THE MODEL OF YY HER AFTER TWO SEASONS
L. Hric,1R. G´alis,2A. Dobrotka,3V. ˇ
Simon,4K. Petr´ık,5P. Niarchos,6Z. Veliˇc,7K. Gazeas,6L. ˇ
Smelcer,8
P. H´ajek,9P. Sobotka,10 K. Koss,9L. Br´at,10 and F. Lomoz10
During two observational seasons of interna-
tional campaign of YY Her we secured pho-
tometric data which covered the primary as
well as the secondary minima and revealed
unexpected outburst activity of this system.
YY Her belongs to the classical symbiotic bina-
ries with nova-like outbursts. Recently Mikolajew-
ska et al. (2002) explained the light variability of
YY Her by combining the ellipsoidal changes and
sinusoidal variations of the nebular continuum and
line emission. In 2001 (Hric et al. 2001) we discov-
ered in the binary system YY Her the presence of the
secondary minimum that was indicated, however, by
only three photometric observations from one obser-
vatory. This uncertainty stimulated us to activate
the international photometric campaign for detailed
covering of the light curve during the period of the
expected secondary minimum.
To this campaign were integrated the following
observatories: Star´a Lesn´a Observatory of the As-
tronomical Institute and Beluˇsa Observatory in Slo-
vakia, University of Athens and Kryonerion Obser-
vatory in Greece as well as Valaˇssk´e Meziˇr´ıˇc´ı Obser-
vatory, Vyˇskov Observatory, N. Copernicus Observa-
tory Brno and Ondˇrejov Observatory of the Astro-
nomical Institute in Czech Republic. We obtained
in this campaign a total of 218, 465, 286 and 291 ob-
servational data in B, V, R and I filter respectively,
that cover the interval of JD 2 451 823 - 2 452 877.
There was a successful campaign conducted to
also cover the primary minimum and it produced
some interesting results. The periodic variations of
the brightness are explained by the eclipses of the
components in the symbiotic system. During the
primary minimum ab out JD 2 452 440 we observed
1Astronomical Institute of the Slovak Academy of Sciences,
059 60 Tatransk´a Lomnica, Slovakia (hric@ta3.sk).
2Faculty of Sciences, University of P. J. ˇ
Saf´arik, 041 54
Koˇsice, Slovakia (galis@kosice.upjs.sk).
3Faculty of Materials Science and Technology STU, 917 24
Trnava, Slovakia (dobrotka@mtf.stuba.sk).
4Astronomical Institute, 251 65 Ondejov, Czech Republic.
5Faculty of Education, 918 43 Trnava University, Slovakia.
6Faculty of Physics, University of Athens, Greece.
7Observatory, 018 61 Beluˇsa, Slovakia.
8Observatory, 757 01 Valaˇssk´e Meziˇr´ıˇc´ı, Czech Republic.
9Observatory, 682 01 Vyˇskov, Czech Republic.
10MEDUZA Group, 616 01 Brno, Czech Republic.
51 900
52000
52100
52200
52300
52 400
52500
52600
52700
52800
52 900
J
D
-
2
4
0
0
0
0
0
15 .5
15 .0
14 .5
14 .0
13 .5
13 .0
12 .5
12 .0
11 .5
11 .0
10 .5
10 .0
9.5
Ma gn it u d e
Y
Y
H
e
r
I
R
V
B
Fig. 1. BVRI photometry of YY Her secured during
international campaign from 2001 to 2003.
the flares that were later followed by the energetic
outburst in about JD 2 452 700.
At the first glance at the light curve it is evident
that the amplitude of the outburst declines towards
longer wavelengths while for the particular colour
the following amplitudes in maximum were detected:
1.56 mag in B, 1.04 in V, 0.54 in R and 0.20 in I fil-
ter respectively. The monotonic decline of brightness
from maximum was interrupted by an apparent dip.
That coincides with the time of the secondary mini-
mum.
In this paper we outlined the idea that the pho-
tometric behaviour of YY Her is possible to describe
consistently by an eclipsing model. This explanation
requires the presence of an optically thick envelope
around the white dwarf with a temperature signifi-
cantly lower than the temperature of the hot compo-
nent. The existence of such an envelope is in agree-
ment with assumptions about steady state burning
of matter accreted on the white dwarf by a red gi-
ant wind. The occasionally observed outbursts are
caused by transfer of blob of matter through L1, by
collision in the ring (the first weaker outburst) and
by following impact on the white dwarf (the second
stronger outburst).
REFERENCES
Hric, L., Petr´ık, K., Niarchos, P., Veliˇc, Z., G´alis, R. 2001,
IBVS No. 5046
Mikolajewska, J., Kolotilov, E.A., Shugarov, S. Yu,
Yudin, B.F. 2002, AA 392, 197
222