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Golysheva P., Shugarov, S., Katysheva N., Chochol D.
Multicolour photometry of unusual dwarf nova star
HS 0218+3229
Sternberg Astronomical Institute, Moscow and Astronomical
Institute of Slovak Academy of Sciences, Tatranska Lomnica
Dwarf Novae
Cataclysmic variables (CVs) are highly evolved close binaries
consisting of a red dwarf transferring a matter to his companion – a
white dwarf. This matter creates an accretion disc around the white
dwarf. Dwarf novae (dNe) are a subclass of cataclysmic variables
(CVs). dNe usually live in quiescence but sometimes flare up. Their
outbursts is caused by accumulation a matter in accretion disc and
possibly a sudden increasing of mass rate. Outbursts of U Gem-, or
SS Cyg-type of dNe last a few days.
h
m
s
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HS 0218+3229 (RA = 2 21 34 , Del = +32 43'.4, J2000) was
suspected as a CV by Gänsicke et al (ASP Conf. Ser., 261, 190,
2002).
Later the system was studied by Rodrigues-Gil et al. (Astron. Ap.
496, 805, 2009). They didn’t observe any outbursts, but their spectral
observations showed the emission lines of hydrogen and neutral
helium of weak accretion disc and the absorption lines of a cold
component.
Rodrigues-Gil et al. determined an orbital period of 0.297 days,
during which a double wave is seen, and valued some parameters
of HS 0218+3229:
They described second component as a K5V star which contributes
of 80-85% to the R-brightness of the system.
i = 59o± 3o
0.52<q<0.65
0.44< M1/MSun <0.65
0.23< M2/MSun<0.44
d= 0.9 - 1 kpc
HS 0218+3229 was also identified as X-ray source
RXS J022133.6+324343 and as IR-source
2MASS J02213348+3243239.

Independently HS 0218+3229 was discovered by
S. Antipin in 2006 yr on the plates of the photo
collections of SAI. He found one outburst with
amplitude 4m.5 in Bpg – band among the 200
photoplates in the interval 1963-1997 yrs.

Then we carried out more than 2000 UBVRI CCD
frames from 2006 to 2010 yrs.

The observations were performed at the 50-cm
telescope in Stara Lesna (Slovakia) and 50- and
125-cm telescopes of Crimean laboratory of SAI.
We began our observations in Sept., 2007. And in October we caught
the outburst of HS 0221. The outburst light curve is present below.
The nightly LCs are in the separate windows. Left LC shows the
orbital wave with the ellipsoidal effect, this effect is not visible on the
other nightly LCs because of the outburst disc.
The UBVRcIc-band light curves from 2006 to 2010 yrs. The
observations in RJ IJ -bands are plotted by grey points.
During outburst
(JD 2454384-385):
Vmax ≈ 12m.34(05)
U ≈ 11m.3±0m.2
B ≈ V ≈ 12m.3(2)
RJ ≈ IJ ≈ 12m.2(2)
At the quiescence
there is a small
variability with an
amplitude of 0m.2
and with a
characteristic time
of hundreds of
days.
Let’s go back to outburst of the October. We can see that the
form of the LC is more symmetrical than the other dNe. Symmetry
coefficient (the ratio of the duration of the ascending branch to
the descending branch) is ~0.22. For famous dN SS Cyg this
value is 0.10-0.13. The length of outburst was valued in 15-16 d.
Such form of the LC HS 0218+3229 can be explained by
the low rate of mass transfer in the system. In this case
it is “inside-out” outburst in accordance with Smak
(PASP, 96, 575, 1984). Outburst starts from the inner
parts of the disk and extends outward.
The nightly light curves are present in the next slides.
The nightly light curves of HS 0218+3229 in quiescence (Mag vs JD)
Some of the curves clearly show a double wave per a period.
The nightly light curves of HS 0218+3229 in quiescence (Mag vs JD).
We can see
the fast
variability in
U, B-bands
with a
characteristic
time of 40-50
min.
Maximum
amplitude in
U-band is of
0m.7, in Bband - 0m.4.
Phased light curves
We got next ephemeris which satisfies both our observations
and data by Rodriguez-Gil et al. (2009) :
The initial epoch of the minimum is the same as in the
paper by Rodriguez-Gil et al. (2009). This epoch
corresponds to the inferior conjunction (the RD before
the WD)
B
V
V
U
U-B
Rc
B-V
Ij
V-Rc
Ic
(R-I)c
The phased LCs are plotted above. Double wave per a period is
clear seen,especially in V, Rc-bands. In the U & B-bands it is not
so obvious but there is some fading at phase 0 .
We can see that the form of LC changed: before outburst the
depths of the main and the secondary minima were different
and the LC amplitude was larger. After outburst the depths and
amplitude of both waves were the same.
There are summed LCs before (grey) and after (black) outburst.
This can be explained by the fact that, immediately before an
outburst, the saturated accretion disk makes a larger contribution
to the luminosity of the system than afterward, when it is
exhausted. The heights of the maxima in the pre-outburst state
are different because we view the region where the stream and
the outer parts of the disk interact from different angles. On the
other hand, the depths of the minima are different because the
“nose” of the red star, which is turned toward the white dwarf, is
heated by radiation from the disk. After an outburst the luminosity
of the disk and the spot on it decrease, and these effects are less
marked. Rodrigues-Gil et al., marked that during JanuaryFebruary 2001, the heights of both maxima and the depths of the
minima were essentially the same, but in October 2005,
differences between them could be seen. These curves are very
similar to our curves constructed using data obtained prior to the
outburst of 2007. It can be assumed that at the end of October
2005 or just after that, the star underwent an outburst that was
missed.
U-B, B-V
U-B
The positions of
HS 0218 at
max, min and at
the decline note
by “ * ”.
Comparison
stars are
marked as the
“diamonds”.
The position of
the star at
maximum is
quite uncertain.
B-V
V-Rj, (R-I)j
V-Rj
At minimum
position of our
system is close
to K5V – K6V
stars.
In the U-B, B-V
diagram the UVexcess caused
by the radiation
of hot outburst
disc is seen.
(R-I)j
Summary
1.We detected two outbursts of HS 0218+3229 in 1980 and
2007 yrs. Once more outburst (in 2002) was found by Р.
Wills in the database NEAT. An duration of 2007 outburst
was 15-16 days and asymmetry coefficient ~0.22. The
amplitudes were maximal in U,B-bands - 5m, and 4m, 3m.5
and 3m in V, R, I, accordingly.
2. In quiescence we can see a double wave per a period. And
we give:
JD(Min I) = 2453653.0286+(0.d2973559±0.0000010)·E
(Porb=7h 8m 11s. 5) .
3. Two-color diagrams show that the star was bluer than during in
quiescence. It is connected with a dotation of bright accretion disc
into total luminosity. Outburst color temperature was of 15000 К.
Color-indices in quiescence correspond to the star К5V.
4. As a result, we classified this cataclysmic variable as a very
rare subtype of UGSS of dNe with low accretion rate and sparse
and more symmetric (“inside-out”) outbursts than usual U Gemand SS Cyg-type dNe have.
5. We also valued some parameters of this binary:
disc luminosity LV = 1.6∙1034 erg/s, Lbol~4∙1034 erg/s,
the orbital size 1.5-1.9 Rsun,
the distance 0.66 kpc
Thanks!