[vsnet-preprint 13] IBVS submission "WY Tri : A New SU UMa-type Dwarf Nova"

["Tonny Vanmunster" <Tonny.Vanmunster@advalvas.be>]

Dear colleagues,

We have pleasure to herewith include a manuscript that has been submitted to
the IBVS. It describes the December 2000 outburst of the cataclysmic
variable WY Tri, including our most important findings on this object.

Kind regards,

Tonny Vanmunster
CBA Belgium Observatory



\documentstyle[twoside,epsf]{article}
\input{ibvs2.sty}
\begin{document}
\IBVShead{XXXX}{XX January 2001}
\IBVStitle{WY Tri : A NEW SU UMa-TYPE DWARF NOVA }
\IBVSauth{Tonny Vanmunster$^1$}
\IBVSinst{Center for Backyard Astrophysics (Belgium),Walhostraat 1A, B-3401
Landen, Belgium, \\ \indent email: Tonny.Vanmunster@advalvas.be}

\IBVSobj{WY Tri}
\IBVStyp{ cataclysmic }
\IBVSkey{Cataclysmic variables -- photometry}

\begintext

WY Tri is an 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
13.8p - $>$ 17.0p. The object has been discovered by L. Meinunger
(Meinunger 1986). Here we report differential time-series photometry of WY
Tri,
obtained at the Belgian observatory of the Center for Backyard Astrophysics
(CBA) during
the December 2000 outburst. We detected superhumps with a period of 0.07847
($\pm$ 0.00002)
d. Our observations thus establish WY Tri as a new member of the SU UMa-type
cataclysmic
variables.

\medskip
\noindent
{\bf Outburst history}

\medskip
WY Tri was discovered by Meinunger in 1986 on plates of a field around
$\beta$ Trianguli,
taken with the 40/160 and 40/195 cm astrographs of Sonneberg Observatory
(Meinunger
1986). 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).

\smallskip
\noindent
5 distinct outbursts of WY Tri are listed by Meinunger, the brightest one
showing the
variable at mag 13.8p, although the average maximum magnitude derived from
his
observations is mag 15.0p 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.

\smallskip
\noindent
The December 2000 outburst of WY Tri was first reported by Jochen Pietz
(Pietz 2000),
who found the object around mag 15.7 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.

\smallskip
\noindent
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 3.2 magnitudes.

\begin{table}
\begin{center}
\begin{tabular}{ccccc}
\hline
UT Date & JD Start$^1$ & Length (hr) & Telescope$^2$ & Points \\
\hline
20-Dec-2000 & 1899.3499 & 4.58 & 1 & 246 \\
21-Dec-2000 & 1900.2334 & 7.87 & 1 & 354 \\
22-Dec-2000 & 1901.2134 & 8.40 & 1 & 391 \\
23-Dec-2000 & 1902.1976 & 8.88 & 1 & 345 \\
\hline \\
\multicolumn{5}{l}{$^1$ 2,450,000+ } \\
\multicolumn{5}{l}{$^2$ (1)=CBA Belgium, 0.35-m } \\
\\
\end{tabular}
\end{center}
\caption{Log of photometry }
\end{table}

\bigskip
\noindent
{\bf CCD photometry during the December 2000 outburst}

\medskip
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).

\medskip
\noindent
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 (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).

\IBVSfig{12.0cm}{wytri-f3.eps}{Light curve of WY Tri.}

\smallskip
During the 4 observing nights, we used GSC 2327 1839 (mag 11.8) as the
comparison star,
whose constancy was confirmed by other check stars. Camera control,
telescope guiding
and photometric imaging were all done using {\it MaxIm DL/CCD} (Cyanogen
Productions
Inc.). Images were stored as FITS files and were corrected for standard
debiasing
and flat fielding. Data reduction was completed using the profile fitting
algorithm
(PSF) of {\it MIPS} (Buil et al. 1993), immediately following image
acquisition,
allowing incoming observations of WY Tri to be monitored in a
quasi-real-time mode.
This approach revealed the 喪eal-timedevelopment of superhumps in the
system and
allowed the immediate classification of the object as a new SU UMa-type
cataclysmic variable (Vanmunster 2000b).

\IBVSfig{8.0cm}{wytri-f1.eps}{Period analysis of WY Tri.}
\IBVSfig{5.0cm}{wytri-f2.eps}{Phase diagram of WY Tri.}

\smallskip
Our December 20, 2000 observations already showed fully grown superhumps
with an
amplitude of 0.39 magnitudes. 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 in 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 0.07847 ($\pm$ 0.00002) d.
The mean waveform of WY Tri is shown in
Figure 3, and is a classical footprint of a common superhump profile. The
superhump
full amplitude was about 0.39 magnitudes.

\medskip
\noindent
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 0.078483 day (Uemura 2000).

\medskip
The December 2000 eruption light curve of WY Tri indicates a maximum
magnitude of
mag 15.1 (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 0.15 mag per day, which is a typical value for dwarf novae
in
superoutburst.

\smallskip
\noindent
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.

\medskip
\noindent
There's 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
\begin{references}

Berg, C., et al., 1992, {\it Astrophys. J. Sup.}, {\bf 78}, 409

Buil, C., Klotz, A. et al., 1993, {\it Manual for the Microcomputer Image
Processing System}, V2.0

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

Meinunger, L., 1986, {\it Mitt. uber veranderliche Sterne}, {\bf 11}, 1

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

Pietz, J., 2000, {\it vsnet-outburst 1179}

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

Uemura, M., 2000, {\it vsnet-campaign-dn 376}

Vanmunster, T., et al., 2000a, {\it IBVS 4940}

Vanmunster, T., 2000b, {\it vsnet-campaign 588}

\end{references}
\end{document}

VSNET Home Page

---

vsnet-adm@kusastro.kyoto-u.ac.jp

VSNET Home Page

Return to Daisaku Nogami

---

vsnet-adm@kusastro.kyoto-u.ac.jp