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[vsnet-preprint 14] J2315.5-3049 preprint
Dear colleagues,
The following article is accepted for publication as IBVS No.5023.
The figure is available at:
http://ftp.kusastro.kyoto-u.ac.jp/pub/vsnet/preprints/J2315_3049/
Best Regards,
Ryoko Ishioka
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\documentstyle[twoside, epsf]{article}
\input ibvs2.sty
\begin{document}
\IBVShead{5023}{00 Month 2001}
\IBVStitle{Unusual Short-Period DWARF NOVA RX J2315.5$-$3049}
\IBVSauth{ISHIOKA, R.$^1$, KATO, T.$^1$,MATSUMOTO, K.$^1$, UEMURA,M.$^1$,
IWAMATSU, H.$^1$, and STUBBINGS, R.$^2$}
\IBVSinst{Dept. of Astronomy, Kyoto University, Kyoto 606-8502, Japan, \\
\ident
e-mail: ishioka@kusastro.kyoto-u.ac.jp,tkato@kusastro.kyoto-u.ac.jp,katsura@kusastro.kyoto-u.ac.jp,\\
uemura@kusastro.kyoto-u.ac.jp,iwamatsu@kusastro.kyotro-u.ac.jp}
\IBVSinst{19 Greenland Drive, Drouin 3818, Victoria, Australia, e-mail: stubbo@sympac.com.au}
\SIMBADobj{RX J2315.5$-$3049}
\IBVSkey{photometry}
\begintext
The ROSAT X-ray source RX J2315.5$-$3049 was identified with a 17.3-mag
cataclysmic variable (Schwope et al., 2000). Schwope et al. (2000)
classfied the object as a dwarf nova.
One of the authors (RS) visually detected first-ever outburst on 2000 July 8
(m$_v$=13.4, Stubbings 2000a) and next outburst on 2000 October 26 (m$_v$=14.0,
Stubbings 2000b). We performed CCD observations on later outburst.
In this paper, we report our CCD observations and some peculiarities of this
object.
The CCD observations were done using $R_c$-filtered PixelVision
camera (SITe SI004AB chip, CryoTiger-cooled) attached to a 60-cm reflector
at Ouda Station (Ohtani et al. 1992) and an $R_c$-filtered ST-7E camera
attached to Meade 25-cm Schmidt-Cassegrain telescope at Kyoto University.
Exposure time was 30\,sec.
The images were dark-subtracted, flat-fielded and analyzed with IRAF APPHOT
package (IRAF is distributed by National Optical Astronomy Observatories in
U.S.A.), and with Java$^{\rm TM}$-based aperture photometry package developed
by one of the authors (TK), respectively.
The differential magnitudes of the variable were measured against the
comparison star GSC 7507.14 (USNO $r$-magnitude 12.1), whose constancy was
confirmed by the check star GSC 7507.708 (USNO $r$-magnitude 12.2).
We performed observations on five nights, but only upper limits were obtained
on two nights. Table 1 is a summary of observations.
The visual observations were done by one of the authors (RS) with a 32-cm
reflector. Magnitudes and upper limits were estimated using $V$-magnitude
comparison stars.
Figure 1 (see Table 2) gives the long-term light curve of RX J2315.5$-$3049
covering 6 months.
The abscissa is time in Julian Date and the ordinate is $m_v$ or
$R_c$-magnitude (the v-mark represent upper limits). Some observations
by A. Pearce and B. Monard were supplied from their reports to VSNET.
Two outbursts are clearly seen.
These observations revealed that RX J2315.5$-$3049 is a dwarf nova with
a recurrent period of about 110\,d, and a range of 13.4-17.3 $m_v$.
The minimum magnitude is taken from the V-magnitude by Schwope et al.(2000).
Figure 2 (see Table 3) gives the light curve of RX J2315.5$-$3049 on Oct. 27.
The abscissa is time in Julian Date and the ordinate is the differential
magnitude of Ouda data (filled circles), Kyoto data (open circles),
or comparison(lines).
Two humps with an amplitude of $\simeq$0.3\,mag and a period of 0.078\,d were
detected. The humps showed a smooth, rapid rise and a slower decline, which
are very characteristic to superhumps in SU UMa-type dwarf novae. We
therefore identify this hump feature as superhumps and consider this outburst
as a superoutburst of an SU UMa-type dwarf nova (for a review of SU UMa-type
dwarf novae and superhumps, see Warner 1995).
\begin{table}
\caption{summary of observations}
\begin{center}
\begin{tabular}{ccccccc}
\hline
start - end & N$^a$ & Exp & Filter & $\sigma^b$ & $\Delta$ mag$^c$ & Site$^d$ \\
(JD$-$2450000) & &(sec) & & (mag) & (mag) & \\
\hline
1844.061 - 1844.063 & 4 & 30.0 & $R_c$ & - & 2.2 & O \\
1844.970 - 1845.093 & 299 & 30.0 & $R_c$ & 0.05 & 1.88 & O \\
1845.035 - 1845.139 & 201 & 30.0 & $R_c$ & 0.3 & 1.87 & K \\
1850.013 - 1850.048 & 17 & 30.0 & $R_c$ & 0.02 & 4.6 & O \\
1856.019 - 1850.022 & 10 & 30.0 & $R_c$ & - & $>$1.5 & K \\
1860.017 - 1860.020 & 10 & 30.0 & $R_c$ & - & $>$2.3 & K \\
\hline
\multicolumn{7}{l}{$^a$ number of frames} \\
\multicolumn{7}{l}{$^b$ standard deviation of differential magnitudes of
the comparison star : comparison$-$check} \\
\multicolumn{7}{l}{$^c$ nightly averaged differential magnitude relative
to GSC7507.14} \\
\multicolumn{7}{l}{$^d$ O: at Ouda, K: at Kyoto} \\
\end{tabular}
\end{center}
\end{table}
However, there are some atypical features. As in Fig. 1, this outburst
faded rapidly (within 9\,d) as if it were an normal outburst, rather
than a long-lasting superoutburst (cf. Warner 1995).
Furthermore, Augeteijin et al. (2000) reported that they have found an
orbital period of 0.058 d based on their photometry and spectroscopy.
Augeteijin et al. (2000) also noted that they detected $\sim$0.3 mag
eclipse-like feature in their quiescent light curve similar to that of
WZ Sge. Our period is $\sim$30\% longer than the reported period. If the
observed features in our outburst photometry are genuine superhumps,
this fractional superhump excess is exceptionally large among all SU UMa-type
dwarf novae (the fractional largest superhump excess in SU UMa-type dwarf
novae was 7.7\% observed in TU Men, cf. Stolz et al. 1984, Nogami et al. 1998).
If this large superhump excess is confirmed, this may require a new mechanism
for exciting superhumps.
The other possible explanation may be that the period detected by
Augeteijin et al. (2000) represents the spin period of an intermediate
polar (IP), and that the period we detected represents the orbital or
superhump period. In this interpretation, the ratio of orbital period
versus spin period, 1.34 for RX J2315.5-3049, is close to 1.46 for EX Hya
(Hellier et al. 1987), the well-known IP below the period gap.
The relatively strong X-ray emission may also be explained
by its suggested IP nature. If the latter possibility is confirmed,
the object makes the second established member of the EX Hya-like IPs.
To understand the nature of RX J2315.5-3049, confirmation of the orbital
period with spectropic or photometric observation is needed.
\IBVSfig{10cm}{ibvs-f1.eps}{Long-term light curve of RX J2315.5$-$3049}
\IBVSfig{10cm}{ibvs-f2.eps}{Short-term light curve on 2000 October 27}
\vskip 1cm
\references
Auguteijin, T., {\it vsnet-campaign}, 544
(http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/Mail/vsnet-campaign/msg00544.html)
Hellier, C., Mason, K. O., and Rosen, S. R., 1987, {\it MNRAS}, {\bf 228}, 463
Nogami, D., Kato, T., Masuda, S., 1998, {\it PASP},{\bf 50}, 411
Ohtani, H., Uesugi, A., Tomita, Y., Yoshida,M.,
Kosugi, G., Noumaru, J., Araya, S., Ohta, K.
1992, {\it Memoirs of the Faculty of Science, Kyoto University,
Series A of Physics, Astrophysics, Geophysics and Chemistry},
{\bf 38}, 167
Schwope, A. D., Hasinger, G., Lehmann, I., Schwarz, R., Brunner, H.,
Neizvestny, S., Ugryumov, A., Balega, Yu.,
Tr{\"{a}}mper, J., Voges, W., {\it AN}, {\bf 321}, 1
Stolz, B., and Schoembs, R., 1984, {\it A\&A}, {\bf 132}, 187
Stubbings, R., 2000a, {\it vsnet-outburst}, 245
(http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/Mail/vsnet-outburst/msg00245.html)
Stubbings, R., 2000b, {\it vsnet-outburst}, 810
(http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/Mail/vsnet-outburst/msg00810.html)
Warner, B., 1995, {\it Cataclysmic Variable Stars (Cambridge University Press,
Cambrige)}
\endreferences
\IBVSedata{Table2.txt}
\IBVSedata{Table3.txt}
\end{document}
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