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\IBVShead{4765}{6 September 1999}

\IBVStitletl{CCD Observation of the 1998 October Superoutburst }{ of PU P\lowercase{er}: Confirmation as an SU UM\lowercase{a}-type Dwarf Nova}

\IBVSauth{T.~Kato, K.~Matsumoto}

\IBVSinsto{Dept.\ of Astronomy, Kyoto University, Kyoto 606-8502, Japan, \\ \indent e-mail: tkato@kusastro.kyoto-u.ac.jp, katsura@kusastro.kyoto-u.ac.jp}

\SIMBADobj{PU Per}
\IBVStyp{ UGSU }
\IBVSkey{Dwarf novae - photometry}

\begintext

PU Per is a dwarf nova discovered by Hoffmeister (1967). The historical record of outbursts, suggesting the SU UMa-type, is reviewed in Kato and Nogami (1995). Kato and Nogami (1995) made time-resolved photometry of the short outburst in 1995 October. On the rapidly decaying stage of the outburst, they detected possible hump-like features with a period of $\sim$0.06~d. The confirmation of the SU UMa-type nature has been thus awaited for.

On 1998 September 25, T. Kinnunen reported the detection of a bright ($m_{\rm v}=14.8$) outburst. Upon this alert, we observed PU Per on three nights of October 2--4. The observations were done using an unfiltered ST-7 camera attached to the Meade 25-cm Schmidt-Cassegrain telescope. The exposure time was 30~s. The images were dark-subtracted, flat-fielded, and
analyzed using the Java$^{\rm TM}$-based PSF photometry package developed
by one of the authors (TK). The flux of the variable was measured relative
to GSC 2337.27 (USNO $r$-magnitude 12.1), whose constancy was confirmed
by comparison with GSC 2337.614 (USNO $r$-magnitude 12.4). The fluxes
given in figures of this note are expressed relative to GSC 2337.27.

Figure 1 illustrates the overall light curve of the present observation.
The light curve shows a steady decline characteristic of superoutbursts.
After subtracting the linear declining trend, the light curve was analyzed using the Phase Dispersion Minimization (PDM) method (Stellingwerf 1978) and LANCELOT (period analysis using artificial neural networks, Gaspani 1995a,b). The resultant theta diagram (PDM) and G(f) function (LANCELOT) are shown in Figure 2. The minimum and maximum points respectively correspond to the best estimates of the period.

The selection of the best superhump period suffers from some difficulties owing to the low signal-to-noise ratio and the gaps caused by clouds. From the three one-day alias candidate periods (0.0686, 0.0733 and 0.0640~d), we have chosen the period $0.0733 \pm 0.0001$ (corresponding to the frequency of 13.64~d$^{-1}$) as the best-determined period, based on the independent superhump detection information (Kemp and Vanmunster, private communication). However, there still remains the possibility for other aliases from the present data set.

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\IBVSfig{9.75cm}{4765-f1.ps}{Overall light curve of PU Per}

\IBVSfig{9.75cm}{4765-f2.ps}{Period analysis of PU Per}

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\IBVSfig{10cm}{4765-f3.ps}{Superhump profile of PU Per}

Figure 3 shows the averaged superhump profile, folded by the period of 0.0733~d. The mean superhump amplitude is $\sim$0.2 magnitude. PU Per can now be safely classified as an SU UMa-type dwarf nova.

\bigskip

This work is partly supported by the Grant-in-Aid for Scientific Research
(10740095) of the Japanese Ministry of Education, Science, Culture, and
Sports (TK). Part of this work is supported by a Research Fellowship of the
Japan Society for the Promotion of Science for Young Scientists (KM).

\references

Gaspani, A., 1995a, {\it GEOS Fiche Technique}, No.\,78

Gaspani, A., 1995b, in {\it ``Proceedings of the 27th Conference on Variable Star Research''} (Brno 1995), p.\ 37

Hoffmeister C., 1967, {\it Astron.\ Nach.}, {\bf 290}, 43

Kato, T., Nogami, D., 1995, {\it IBVS}, No.\,4260

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

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