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\IBVShead{5031}{16 February 2001}
\IBVStitle{WY T\lowercase{ri}: a New SU UM\lowercase{a}-type Dwarf Nova} 

\IBVSauth{Vanmunster, Tonny}
\IBVSinsto{Center for Backyard Astrophysics (Belgium), Walhostraat 1A, B-3401 
Landen, Belgium\\ \indent email: Tonny.Vanmunster@advalvas.be}

\SIMBADobj{WY Tri}
\IBVStyp{ cataclysmic }
\IBVSkey{Cataclysmic variables - photometry}
\IBVSabs{Here we report differential time-series photometry of WY Tri, obtained}
\IBVSabs{at the Belgian observatory of the Center for Backyard Astrophysics}
\IBVSabs{(CBA) during the December 2000 outburst. We detected superhumps with a}
\IBVSabs{period of 0.07847d +- 0.00002d). Our observations thus establish}
\IBVSabs{WY Tri as a new member of the SU UMa-type cataclysmic variables.}

\begintext

WY Tri is a UG-type cataclysmic variable (Downes et al.\ 1997) located
at $\alpha = 02\hr 25\mm 00\fsec 57$, $\delta = +32\deg 59\arcm
54\farcs 9$ (J2000.0), with a magnitude range of 13.8 -- $>$17.0 $\rm
m_{pg}$.  The object has been discovered by L. Meinunger (Meinunger
1986) in 1986 on plates of a field around $\beta$ Trianguli, taken with
the 40/160 and 40/195-cm astrographs of Sonneberg Observatory.
Meinunger recognised the UG type of variability and gave the object the
preliminary designation S 10919. He also published a finding chart, and
noted that the variable is visible at minimum light on Palomar Atlas
charts as a blue object. A detailed finding chart is given in (Downes
et al.\ 1997).

Five distinct outbursts of WY Tri are listed by Meinunger, the
brightest one showing the variable at 13.8 $\rm m_{pg}$, although the
average maximum magnitude derived from his observations is 15.0 $\rm
m_{pg}$ only.  Apart from this, very little seems to have been
published about the outbursting characteristics of WY Tri. More
recently, the object has received some attention from amateur variable
star observers around the world.

The shortest likely interval between outbursts of WY Tri is about 381
days, but from the sparse observations it is impossible to conclude
whether this is the true outburst cycle of the object, or just a
multiple. More intensive monitoring of WY Tri will be required to
derive the precise values of the outburst and superoutburst cycles.
The outburst amplitude is over 3\fmm2.

The December 2000 outburst of WY Tri was first reported by Jochen Pietz
(Pietz 2000), who found the object around  15\fmm7 on unfiltered CCD
images taken on 2000, December 16.914 UT\@. For the first time, this
outburst was monitored intensively by CCD photometry, the results of
which are discussed below.

\begin{table}
\caption{Log of photometry}
\begin{center}
\begin{tabular}{ccccc}
\hline
UT Date & JD Start & Length (hr) & Points \\
\hline
20-Dec-2000 & 2451899.3499 & 4.58 & 246 \\
21-Dec-2000 & 2451900.2334 & 7.87 & 354 \\
22-Dec-2000 & 2451901.2134 & 8.40 & 391 \\
23-Dec-2000 & 2451902.1976 & 8.88 & 345 \\
\hline \\
\\
\end{tabular}
\end{center}
\end{table}

Upon notification of the outburst of WY Tri through VSNET (Pietz 2000),
an observing campaign was launched at the Belgian node of the Center
for Backyard Astrophysics (CBA)\@. The CBA is a multi-longitude network
of professional and amateur astronomers (Patterson 1998), who study
periodic phenomena in cataclysmic variables. Target campaigns and
results of the CBA are regularly reviewed on the CBA Web site
(http://cba.phys.columbia.edu).

\IBVSfig{14cm}{5031-f1.eps}{Light curve of WY Tri}
\IBVSfig{8cm}{5031-f2.eps}{Period analysis of WY Tri}
\IBVSfig{8cm}{5031-f3.eps}{Averaged phase diagram of WY Tri}

\vskip-36pt
The CBA campaign on WY Tri occurred during very favourable conditions,
with the variable being visible almost all night long. We accumulated
29.7 hours of coverage over 4 nights and obtained 1336 datapoints.
Details are listed in Table~1.  Time-resolved and differential
($\rm variable - comparison$) CCD photometry of WY Tri was done at CBA
Belgium using a 0.35-m $f/6.3$ Schmidt-+Cassegrain telescope, mounted on
an AstroTechniek FM-98 German equatorial mount, and equipped with a
SBIG ST-7 CCD camera (Kodak KAF-0400 CCD for imaging and Texas
Instruments TC211 CCD for guiding). For a complete description of the
CBA Belgium Observatory equipment and software, see (Vanmunster et al.\
2000a). During the 4 observing nights, we used GSC 2327 1839 (11\fmm8)
as the comparison star, whose constancy was confirmed by other check
stars.

Our December 20, 2000 observations revealed already fully grown
superhumps with an amplitude of 0\fmm39, and allowed the
immediate classification of the object as a new SU UMa-type cataclysmic
variable (Vanmunster 2000b).  The initial stage of the outburst
probably has been missed. Further observations at CBA Belgium were
obtained over the next nights (Figure~1), allowing a more detailed
analysis of the superhump period. After removing linear trends from the
light curve, we performed a period analysis using the Phase Dispersion
Minimization PDM method (Stellingwerf 1978). The resulting theta
diagram is shown in Figure~2. The best superhump period is $0\fday07847
\mathbin{(\pm} 0\fday00002)$.  The mean waveform of WY Tri is shown in Figure~3
(averaged data), and is a classical footprint of a common superhump
profile. The superhump full amplitude was about 0\fmm39.

The above superhump period value is in good agreement with results
obtained at other observatories during the December 2000 outburst of WY
Tri. In particular, data from Kyoto University, Japan and Copernicus
Observatory, Czech Republic, yielded a superhump period of 0\fday078483
(Uemura 2000).

The December 2000 eruption light curve of WY Tri indicates a maximum
magnitude of 15\fmm1 (unfiltered CCD images), but since parts of the
initial outburst phase likely have been missed, it is uncertain if this
represents the true maximum magnitude value attained by the variable.
The final fading of the object took place with an average decline rate
of 0\fmm15 per day, which is a typical value for dwarf novae in
superoutburst.

We also examined the post-superoutburst behaviour of WY Tri, as some SU
UMa-type dwarf novae are known to show rebrightenings during this
stage. However, no evidence of such a rebrightening was found, both in
our own CCD monitoring during two weeks following the steep decline,
and in reports submitted to VSNET.

There is still an important amount of characteristics of WY Tri to be
uncovered.  Therefore, this object should receive all possible
attention from both amateur and professional astronomers.

\bigskip
{\bf Acknowledgements.} We are grateful to the Center for Backyard Astrophysics
for their continuous support in our stellar CCD photometry research work. 

\medskip
\references

Downes, R., Webbink, R., Shara, M., 1997, {\it PASP}, {\bf 109}, 345 

Meinunger, L., 1986, {\it Mitt.\ ver\"anderliche Sterne}, {\bf 11}, 1
% Original: Meinunger, L., 1986, {\it Mitt.\ \"uber ver\"anderliche Sterne}, {\bf 11}, 1
% Corrected: Thu Aug 14 10:24:38 MET DST 2003

Patterson, J., 1998, {\it Sky and Telescope}, {\bf October}, 77

Pietz, J., 2000, vsnet-outburst, No. 1179 \ \ \  ({\tt 
http://www.kusastro.kyoto-u.ac.jp/ vsnet/Mail/vsnet-outburst/msg01179.html})

Stellingwerf, R.F., 1978, {\it ApJ}, {\bf 224}, 953

Uemura, M., 2000, vsnet-campaign-dn, No. 376 ({\tt 
http://www.kusastro.kyoto-u.ac.jp/ vsnet/Mail/vsnet-campaign-dn/msg00376.html})

Vanmunster, T., et al., 2000a, {\it IBVS}, No.\ 4940

Vanmunster, T., 2000b, vsnet-campaign, No. 588 ({\tt 
http://www.kusastro.kyoto-u.ac.jp/ vsnet/Mail/vsnet-campaign/msg00588.html})

\endreferences
\end{document}
