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\IBVShead{4637}{1 October 1998}

\IBVStitle{The superhumps in V592 Herculis\IBVSfm}

\IBVSfoot{Based on observations collected at the European Southern Observatory, La Silla, Chile}


\IBVSauth{H.W.~DUERBECK$^{1,2}$, R.E.~MENNICKENT$^3$}

\IBVSinst{PF 1268, D-54543 Daun, Germany, e-mail: hilmar@uni-muenster.de}
\IBVSinst{affiliated with Muenster University, Germany}
\IBVSinst{Center for Astrophysics, Harvard University, Cambridge, MA 02138, 
USA,\\
\hspace*{0.8cm}e-mail: rmennickent@cfa.harvard.edu}

\SIMBADobj{V592 Her}
\IBVStyp{ DN/SU UMa type }
\IBVSkey{photometry}
\IBVSabs{An analysis of superhumps observed during the recent outburst of}
\IBVSabs{the SU UMa/WZ Sge-type dwarf nova V592 Her is reported.}

\begintext

The first outburst of V592 Her, recorded on Sonneberg plates of 1986,
was discovered by Richter (1968). He classified the object as
a nova. Later it was re-classified as dwarf nova or x-ray nova 
because of the shape of its light curve and the blue colour at 
maximum (Duerbeck 1987).
A second outburst in 1986 was reported by Richter (1991). 
The rareness of outbursts and their large amplitude 
of about 10 magnitudes led Richter (1991)
to re-classify it as recurrent nova or dwarf nova of long
cycle time. 
V592 Her is a potential member of the dwarf nova subtype SU UMa 
(see, e.g., Warner 1995) -- similar to the group of WZ Sge stars,
which show rare superoutbursts, but not normal ones.

The most recent outburst started on 1998 August 26.8 (UT), was reported 
by T.~Kinnunen (Waagen 1998), and followed by spectroscopy (R.M.) and 
photometry (H.D.). Here we present results of the photometric observations.

Differential CCD photometry in B and V was carried out with the 0.91\,m 
Dutch telescope at ESO La Silla. Exposure times were 120\,s for the V 
and 180\,s for the B frames. Sky conditions were not always photometric.
The position of the object in the northern evening sky 
permitted runs of about 90 minutes duration. This was sufficient 
to obtain light curves which clearly show brightness variations. 

Photometric reductions were made using daophot in PC-IRAF\footnote{
IRAF is distributed by the National Optical Astronomy Observatories,
    which are operated by the Association of Universities for Research
    in Astronomy, Inc., under cooperative agreement with the National
    Science Foundation.}.
Magnitude differences between V592 Her and the mean of the two 
$15^{\rm m}$ comparison stars USNO-A1.0 
U1050\raisebox{-1ex}{--}08092747 and U1050\raisebox{-1ex}{--}09092380,
located north-west and south-west of the variable, were derived. 
Light curves, which show the presence of superhumps, are displayed 
in Fig.~1. Individual data will be published in a forthcoming catalogue 
of long-term photometry of variables (Sterken et al. 1998).


\IBVSfig{8cm}{4637-f1.ps}{Light curves of V592 Her at superoutburst during the nights
1998 Sept. 7/8, 8/9 and 10/11. V~magnitudes are shown as filled circles, 
B~magnitudes as open circles, shifted by 0\fmm 4 to fainter values. 
Magnitude differences are relative to the two comparison stars, as 
described in the text. Note the breaks in the time axis}

The form and strength of the superhumps are different in the three nights.
Similar variations, also observed in other SU UMa type dwarf novae
like HV Vir (Leibowitz et al.~1994), are likely caused by a beat 
phenomenon between superhump and orbital periods.  

A straight line fit was subtracted from the photometric data of the three 
nights, and the resulting brightness variations were analyzed, using the 
Period98 programme (Sperl 1997). The most likely
period was found to be 0.06005 day in V, and 0.06378 day in B.
Other neighbouring 
aliases, 0.05667 and 0.06812 days, can be rejected with high probability. 
The times of maximum light, averaged from the two light curves, are
J.D.~hel.~(max) = 2\,451\,064.4852, 2\,451\,065.5074, and 2\,451\,067.4888.
Using the first and last of these times, 
the improved possible superhump periods
are $P=0.06007$ and $0.06391$ days, respectively, 
with errors of about $\pm 0.0002$ day.

If we assume that $P=0.06007$ day is the correct superhump period, the 
predicted orbital period is $P_{\rm orb} = 0.05898$ day (1.416 hrs), 
according to the recent calibration of the Schoembs-Stolz relation 
(Arenas \& Mennickent 1998). The longer period predicts the
orbital period 0.06239 day (1.497 hrs). 

If V592 Her belongs to the WZ Sge group of SU UMa stars,
whose members only show the rare superoutbursts and have orbital 
periods in the range 1.25 and 1.39 hours, the
superhump period of 0.06007 days is favored. 
Additional observations of superhumps and photometry
at the very faint (23\mm) 
minimum stage may give an unambiguous answer.



\vskip 1cm

Acknowledgements. The observations were carried out in the framework of 
the Long-Term Photometry of Variables project by Sterken et al. Its
ESO reference is 61.D-0128. R.M. acknowledges support by Fondecyt grant
1971064 and DIUC grant 97.11.20-1.


\references

Arenas, J., Mennickent, R.E., 1998, {\it A\&A}, {\bf 337}, 472

Duerbeck, H.W., 1987, {\it Space Science Rev.}, {\bf 45}, 1

Leibowitz, E.M., Mendelson, H., Bruch, A., Duerbeck, H.W., 
Seitter, W.C., Richter, G.A., 1994, {\it ApJ}, {\bf 421}, 771

Richter, G.A., 1968, {\it IBVS}, No.\,293

Richter, G.A., 1991, {\it IBVS}, No.\,3619

Sperl, M., 1997, http://dsn.ast.univie.ac.at/$\sim$period98/

Sterken, C., et al., 1998, in preparation

Waagen, E.O., 1998, {\it IAU Circ.}, 7002

Warner, B., 1995, {\it Cataclysmic Variable Stars}, Cambridge: Cambridge 
University Press


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