[Message Prev][Message Next][Thread Prev][Thread Next][Message Index][Thread Index]
[vsnet-preprint 37] HS Vir preprint (cycle length)
Dear Colleagues,
The following article is accepted for publication as IBVS No. 5109.
The figures are placed at:
http://ftp.kusastro.kyoto-u.ac.jp/pub/vsnet/preprints/HS_Vir-cycle/
Regards,
Taichi Kato
===
\documentstyle[twoside,epsf]{article}
\input{ibvs2.sty}
\begin{document}
\IBVShead{xxxx}{xx June 2001}
\IBVStitle{On the supercycle length of HS Vir}
\IBVSauth{Kato,~Taichi$^1$, Stubbings,~Rod$^2$, Pearce,~Andrew$^3$, Dubovsky,~Pavol~A.$^4$, \\
Kiyota,~Seiichiro$^5$, Itoh,~Hiroshi$^6$, Simonsen,~Mike$^7$}
\vskip 5mm
\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{32 Monash Ave, Nedlands, WA 6009, Australia,
e-mail: Andrew.Pearce@worley.com.au} % PEA
\IBVSinst{MEDUZA group, Vedecko-kulturne centrum na Orave,
027 42 Podbiel 194, Slovakia
e-mail: vkco@isternet.sk} % DPV
\IBVSinst{Variable Star Observers League in Japan (VSOLJ),
1-401-810 Azuma, Tsukuba, 305-0031, Japan,
e-mail: skiyota@nias.affrc.go.jp} % Kis
\IBVSinst{Variable Star Observers League in Japan (VSOLJ),
Nishiteragata-cho 1001-105, Hachioji, Tokyo, 192-0153, Japan,
e-mail: PXB02072@nifty.ne.jp} % Ioh
\IBVSinst{46394 Roanne Drive Macomb, MI USA 48044
e-mail: mikesimonsen@mindspring.com} % SXN
\IBVSobj{HS Vir}
\IBVStyp{UGSU}
\IBVSkey{dwarf novae -- photometry}
\begintext
HS Vir is a dwarf nova originally discovered as an ultraviolet excess
object PG~1341$-$079, whose cataclysmic nature was subsequently identified
by spectroscopy (Green et al. 1982, 1986). The first extensive photographic
observations were done by Osminkin (1985), which revealed the existence
of relatively frequent, short, faint outbursts, and the presence of
a bright ($\sim$12.8 mag) outburst. This outburst pattern, together with
the likely orbital period of 0.0836 d (or its alias) from radial-velocity
study by Ringwald (1993), makes HS Vir a good candidate for an SU UMa-type
dwarf nova. However, it took a relatively long time before the nature
of the object is revealed. Kato et al. (1995) reported frequent short
outbursts with a recurrence period of 8 d, but no apparent superoutburst
was recorded. Kato et al. (1998) finally identified a superoutburst
occurring in 1996 May. In spite of their long-term coverage, no additional
superoutburst was observed. Kato et al. (1998) only concluded that the
supercycle of HS Vir should be longer than 80 d. As discussed in
Nogami et al. (1997), Kato et al. (2000) and also Kato et al (1998),
HS Vir has been proposed as an intermediate object between usual
SU UMa-type dwarf novae and peculiar ER UMa stars (for a review, see
Kato et al. 1999). Determination of supercycle of HS Vir thus has been
a long-wanted job.
\vskip 3mm
Since the identification as an SU UMa-type dwarf nova, this star has
been monitored as a part of the VSNET Collaboration
(http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/). The visual and observations were
done with 32-cm (R.S.), 40-cm (A.P.), 20-cm (P.A.D.), 30-cm (H.I.) and
25-cm (M.S.) reflectors. The CCD observations were done using an Apogee
AP-7 attached to a 25-cm telescope (S.K.). An $V$-band filter was used
for the CCD observations. All observations used comparison stars calibrated
in the $V$-band. Nightly averaged magnitudes for CCD observations were
used for the following analysis. Three additional superoutbursts were
recorded up to 2001 June. Table 1 lists the known of superoutbursts
of HS Vir.
\begin{table}
\begin{center}
Table 1. Superoutbursts of HS Vir \\
\vspace{10pt}
\begin{tabular}{ccc}
\hline
JD maximum & peak magnitude & source \\
\hline
2450154 & 13.6 & Kato et al. (1998) \\
2451316 & 13.4 & this work \\
2451689 & 13.3 & this work \\
2452058 & 13.3 & this work \\
\hline
\end{tabular}
\end{center}
\end{table}
\vskip 3mm
As is already evident from Table 1, there is a clear cycle of 371 d,
determined from the recent three superoutbursts. The superoutburst
detected by Kato et al. (1998) also approximately fits to this period.
By assuming three supercycles between the first and second superoutbursts,
the mean cycle length becomes 382 d. However, this value should be
treated with caution since Kato et al. (1998) reported a change in
the outburst characteristics in 1997. The best determined supercycle
of HS Vir is thus 371 d or its $N$-th. While available observations
can reject periods shorter than 124 d (one-third of 371 d), the half
period of 186 d can not be excluded because of observational gaps around
solar conjunctions. Since the period of 371 d is close to one year,
the clear discrimination of these possibilities might be hard to achieve
in the near future. We therefore consider on two possibilities: 186-d
supercycle and 371-d supercycle. Figure 1 and 2 represent folded light
curves by two candidate periods of 186 d and 371 d, respectively.
Only positive observations are plotted in order to avoid confusion.
\IBVSfig{8cm}{fig1.ps}{Light curve of HS Vir folded by a period of 186 d.}
\IBVSfig{8cm}{fig2.ps}{Light curve of HS Vir folded by a period of 371 d.}
\vskip 3mm
Both figures are acceptable for a supercycle light curve of an
SU UMa-type dwarf nova. Because normal outbursts are faint and short,
many of them must have escaped from the present detection.
Given the cycle length of 8 d (Kato et al. 1995) for normal outbursts,
the number ratios of (normal outbursts)/(superoutbursts) become $\sim$23
and $\sim$46 for the periods of 186 d and 371 d, respectively.
These values are rather large compared to most of SU UMa-type dwarf novae
(e.g. Nogami et al. 1997). However, the latter large value is not
perfectly exceptional, as WX Hyi is another example showing a large
number ratio of (normal outbursts)/(superoutbursts). Given the long
orbital period of 0.07692 d (Mennickent et al. 1999), HS Vir may be a
system marginally unstable to the tidal instability, lying close to the
border of SU UMa-type and SS Cyg-type dwarf novae.
\references
Green, R. F., Ferguson, D. H., Libert, J., Schmidt, M., 1982, PASP,
94, 560.
Green, R. F., Schmidt, M., Liebert, J., 1986, ApJS, 61, 305
Kato, T., Hanson, G., Poyner, G., Muyllaert, E., Reszelski, M.,
Dubovsky, P. A., 2000, IBVS, No. 4932
Kato, T., Nogami, D., Masuda, S., Hirata, R., 1995, IBVS No. 4193
Kato, T., Nogami, D., Masuda, S., Baba, H., 1998, PASP, 110, 1400
Kato, T., Nogami, D., Baba, H., Masuda, S., Matsumoto, K., Kunjaya, C.,
1999, {\it Disk Instabilities in Close Binary Systems}, p45, eds.
S. Mineshige, J. C. Wheeler (Universal Academy Press, Tokyo)
Mennickent, R. E., Matsumoto, K., Arenas, J., 1999, A\&A, 348, 466
Nogami, D., Masuda, S., Kato, T., 1997, PASP, 109, 1114
Osminkin, E. Yu., 1985, Perem. Zvezdy, 22, 261
Ringwald, F. A. 1993, Ph. D. thesis, Dartmouth College
\end{document}
vsnet-adm@kusastro.kyoto-u.ac.jp
Return to Daisaku Nogami
vsnet-adm@kusastro.kyoto-u.ac.jp
VSNET Home Page