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[vsnet-preprint 56] V2051 Oph, IY UMa supercycle preprint
V2051 Oph, IY UMa supercycle preprint
Dear Colleagues,
The following article is accepted for publication as IBVS No. 5159.
The figures are available at
http://ftp.kusastro.kyoto-u.ac.jp/pub/vsnet/preprints/V2051_Oph-cycle/
Regards,
Taichi Kato
---
\documentstyle[twoside, epsf]{article}
\input{ibvs2.sty}
\begin{document}
\IBVShead{xxxx}{xx August 2001}
\IBVStitletl{On the supercycle of two eclipsing SU UMa-type}\
{dwarf novae: V2051 Oph and IY UMa}
\IBVSauth{Kato,~Taichi$^1$, Stubbings,~Rod$^2$, Nelson,~Peter$^3$, Pearce,~Andrew$^4$, \\
Garradd,~Gordon$^5$, Kiyota,~Seiichiro$^6$}
\IBVSinst{Dept. of Astronomy, Kyoto University, Kyoto 606-8502, Japan,
e-mail: tkato@kusastro.kyoto-u.ac.jp}
\IBVSinst{19 Greenland Drive, Drouin 3818, Victoria, Australia,
e-mail: stubbo@qedsystems.com.au} % Stu
\IBVSinst{RMB 2493, Ellinbank 3820,Australia,
e-mail: pnelson@dcsi.net.au} % NEL
\IBVSinst{32 Monash Ave, Nedlands, WA 6009, Australia,
e-mail: Andrew.Pearce@worley.com.au} % Pea
\IBVSinst{PO Box 157, NSW 2340, Australia,
e-mail: loomberah@ozemail.com.au} % GAR
\IBVSinst{Variable Star Observers League in Japan (VSOLJ),
1-401-810 Azuma, Tsukuba, 305-0031, Japan,
e-mail: skiyota@nias.affrc.go.jp} % Kis
\IBVSobj{V2051 Oph}
\IBVStyp{UGSU+E}
\IBVSobj{IY UMa}
\IBVStyp{UGSU+E}
\IBVSkey{dwarf novae -- photometry}
\begintext
V2051 Oph is a short-period eclipsing cataclysmic variable whose
exact nature was a matter of controversy for a long time. Some authors
suspected it to be a dwarf nova, while extensive studies by Warner
and O'Donoghue (1987) proposed a low-field polar (synchronously rotating
magnetic cataclysmic variable). It was only recently that regular
detections of outbursts by amateur astronomers confirmed the dwarf nova
nature, and finally Kiyota and Kato (1998) discovered superhumps,
which led to a conclusion to the long-lasting controversy. The star
is now recognized as a member of rare class of SU UMa-type dwarf novae,
which show deep eclipses even during outbursts. Only a handful of
such objects are known: Z Cha, OY Car, HT Cas, DV UMa and IY UMa,
the last one of which will be discussed later in this paper.
All of them have provided a wealth information about the structure of
accretion disks.
\vskip 3mm
Since past observation of V2051 Oph suggested relatively unusual
spectroscopic and photometric features (Warner and O'Donoghue 1987),
the next question is whether V2051 Oph shows typical outburst behavior
as seen in other SU UMa-type dwarf novae. Thanks to the recent intensive
visual monitoring, as a part of VSNET Collaboration \\
(http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/), many outbursts have been
detected. However, since V2051 Oph lies close to the ecliptic, some
outbursts are inevitably missed because of solar conjunctions and
the interference by the Moon. Table 1 lists the detected outbursts
since 1997 August. V2051 Oph was sometimes more frequently detected
around 14.5 mag, than in other observing seasons. It is not clear whether
these detections were short normal outbursts, or enhanced activity in
quiescence, as is sometimes observed in high-inclination systems
(cf. Richter and Greiner (1995) for alternations between high/low states
in a high-inclination dwarf nova, IR Com; see also
http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/LClast/index/PEGIP.html for
a recent example of IP Peg).
Figure 1 shows the light curve drawn from these data. CCD observations
(G.G. and S.K.) are also plotted. Large dispersions of magnitudes
in most part reflect orbital variations caused by eclipses.
\IBVSfig{9cm}{fig1.eps}{Overall light curve of V2051 Oph. Filled and
open symbols represent CCD and visual observations, respectively.
The superoutbursts are marked with ticks. Upper limit observations are
not plotted for simplicity.}
\vskip 3mm
As is evident from Table 1 and Figure 1, four definite superoutbursts
were observed. The shortest interval between them was 201 d. The interval
between the first and second being close to the double this period,
there should have been a missed superoutburst during the conjunction
period. The average supercycle, by assuming this presumably missed
superoutburst, is 227 d. This is a quite typical supercycle for
a relatively active SU UMa type dwarf nova (cf. Nogami et al. 1997).
The cycle length of normal outbursts is more difficult to determine,
but since the epochs of the first seven outbursts are well represented
by a period of 45 d, this period may be a good candidate for
the cycle length. However, if fainter brightenings to $\sim$14.5 mag,
observed between JD 2451110 and 2451777, are indeed normal outbursts,
the cycle length of normal outbursts may need to be halved. In either
cases, both the supercycle length and the cycle length of normal
outbursts fall within a region occupied by usual SU UMa-type dwarf
novae (cf. Nogami et al. 1997). This suggests that V2051 Oph is a
fairly normal SU UMa-type dwarf nova, in terms of its outburst activity.
This existence of a bright deeply eclipsing, fairly normal SU UMa-type
dwarf nova would provide a promising tool for future detailed observations
of accretion process in cataclysmic variables.
\begin{table}
\begin{center}
Table 1. Outbursts of V2051 Oph \\
\vspace{10pt}
\begin{tabular}{cccccccc}
\hline
JD start & peak mag & d$^a$ (d) & type &
JD start & peak mag & d$^a$ (d) & type \\
\hline
2450626 & 13.8 & 3 & normal & 2451313 & 13.2 & 2 & normal \\
2450668 & 13.6 & 3 & normal & 2451340 & 14.6 & 1 & normal$^c$ \\
2450715 & 14.1 & 2 & normal & 2451385 & 12.9 & 8 & super \\
2450900 & 13.6 & 1 & normal & 2451649 & 11.6 & 11 & super \\
2450950 & 11.7 & 13 & super & 2451674 & 13.9 & 1 & normal \\
2450996 & 13.2 & 3 & normal & 2451697 & 14.3 & 1 & normal$^c$ \\
2451030 & 13.4 & 3 & normal & 2451747 & 14.3 & 2 & normal \\
2451071 & 12.8 & 2 & normal & 2451756 & 13.8 & 3 & normal \\
2451110 & 14.0 & 1$^b$ & normal & 2451777 & 14.5 & 2 & normal$^c$ \\
2451227 & 14.7 & 3 & normal$^c$ & 2451850 & 11.9 & $>$3 & super \\
2451254 & 13.7 & $>$1 & normal & 2452024 & 14.0 & 1 & normal \\
2451280 & 14.8 & 2 & normal$^c$ & & & & \\
\hline
\multicolumn{8}{l}{$^{a}$ Duration of outburst (brighter than mag 15).} \\
\multicolumn{8}{l}{$^{b}$ Single estimate.} \\
\multicolumn{8}{l}{$^{c}$ Enhanced activity in quiescence?} \\
\end{tabular}
\end{center}
\end{table}
\vskip 3mm
IY UMa (=TmzV85) was discovered by Takamizawa as a dwarf nova.
Subsequent observations during the 2000 January outburst revealed
that the object is a rare, deeply eclipsing SU UMa-type dwarf nova
(Uemura et al. 2000a,b). Based on the observations of this superoutburst
and other information, a number of authors suggested that IY UMa
has a supercycle length comparable to southern eclipsing SU UMa-type
dwarf novae (Uemura et al. 2000b; Patterson et al. 2000). However,
the reliable determination of the supercycle length should require
further detections of superoutbursts.
Base on the observations reported to the VSNET Collaboration, we have
been able to identify seven outbursts (Table 2 and Figure 2), three of
which (even disregarding the initial detection by Takamizawa) are
superoutbursts.
The last three superoutbursts occurred with a rigorous recurrent period
of 285.5 d. Takamizawa's initial detection could be a superoutburst
three cycles before the JD 2451557, but this is not conclusive because
of a rather large $O-C$ of 61 d against the recent ephemeris. Whether
this could represent a change in the supercycle length needs to be
tested by future observations.
The shortest interval between successive outbursts, including normal
outbursts, was 69 d. This cycle length of normal outbursts is typical
for an SU UMa-type dwarf nova with a supercycle length of 285.5 d.
In conclusion, IY UMa is confirmed to be the first, long-wanted,
deeply eclipsing bright SU UMa-type dwarf nova in the northern hemisphere,
which has typical outburst characteristics of a normal SU UMa-type
dwarf nova.
\begin{table}
\begin{center}
Table 2. Outbursts of IY UMa \\
\vspace{10pt}
\begin{tabular}{cccccccc}
\hline
JD start & peak mag & d$^a$ (d) & type &
JD start & peak mag & d$^a$ (d) & type \\
\hline
2450762 & 13.0 & - & super? & 2451885 & 14.6$^b$ & - & normal \\
2451557 & 14.0 & 14 & super & 2451973 & 14.3 & 2 & normal \\
2451654 & 13.4 & 3 & normal & 2452074 & 13.5 & $>$10 & super \\
2451816 & 13.0 & $>$11 & super & & & & \\
\hline
\multicolumn{4}{l}{$^{a}$ Duration of outburst.} \\
\multicolumn{4}{l}{$^{b}$ Single observation.} \\
\end{tabular}
\end{center}
\end{table}
\IBVSfig{9cm}{fig2.eps}{Overall light curve of IY UMa. Filled and
open symbols represent CCD and visual observations, respectively.
The first two open triangles are photographic discovery observations
by Takamizawa.
The superoutbursts are marked with ticks. Upper limit observations are
not plotted for simplicity.}
\vskip 3mm
The authors are grateful to VSNET members (P. F. Williams, D. Overbeek,
S. Takahashi, M. Watanabe and T. Watanabe) for providing additional
data on V2051 Oph and to T. Kinnunen, P. Schmeer, M. Reszelski,
P. A. Dubovsky, R. J. Modic, M. Simonsen and a number of other observers
for providing crucial observations of IY UMa.
\references
Kiyota, S., Kato, T., 1998, IBVS No. 4644
Nogami, D., Masuda, S., Kato, T., 1997, PASP, 109, 1114
Patterson, J., Kemp, J., Jensen, L., Vanmunster, T., Skillman, D. R.,
Martin, B., Fried, R., Thorstensen, J. R.. 2000, PASP, 112, 1567
Richter, G. A., Greiner, J., 1995, {\it Cataclysmic Variables}, ed
A. Bianchini, M. Della Valle \& M. Orio (Kluwer Academic Publishers,
Dordrecht), p177
Uemura, M., Kato, T., Nov\'{a}k, R., Jensen, L. T., Takamizawa, K.,
Schmeer, P., Yamaoka, H., Henden, A., 2000a, IAUC No. 7349
Uemura, M.; Kato, T., Matsumoto, K., Takamizawa, K., Schmeer, P.,
Jensen, L. T., Vanmunster, T., Nov\'{a}k, R., Martin, B., Pietz, J.,
Buczynski, D., Kinnunen, T., Moilanen, M., Oksanen, A., Cook, L. M.,
Watanabe, T., Maehara, H., Itoh, H., 2000b, PASJ, 52, 9L
Warner, B., O'Donoghue, D., 1987, MNRAS, 224, 733
\end{document}
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