ABSTRACT:More than 230 hours of unfiltered photometry has been collected by several different observers who are part of the Center for Backyard Astrophysics (CAB) network. The data spans the October 1999 outburst of IP Pegasi and presents a new period determination for the system that is in good agreement with previously published periods. The data does not support the detection of Superhumps (SH's) during the outburst phase for this system.
1. INTRODUCTION
IP Pegasi (a(2000):23 23 08.7; d(2000): +18 24 59) was found to be a Cataclysmic Variable system in 1981 (Lipovetskij & Stepanyan 1981) and has subsequently been studied by a number of researchers. Although IP Pegasi displays relatively weak outbursts (2 mag brightening on average) its period of 0.1582 d makes it the only known dawrf nova with an orbital period exceeding the period gap in the orbital period distribution for cataclysmic variables (Harlaftis et al. 1994). IP Pegasi has been the object of a number of Doppler Tomographic studies (Armitage & Murray 1998) and Eclipse Mapping investigations (Bobinger et al. 1997) which have lead to the suggestion that, during outburst, the accretion disk is dominated by a bright spiral shock established via tidal interaction between the donor star and the disk. In this report we present a new period for the system as well as a discussion of the attempt to detect superhump activity during the October 1999 outburst phase.
2. OBSERVATIONS
Members of the Center for Backyard Astrophysics (http://keats.astro.bio2.edu/cba/) observed IP Pegasi over a 3 month span and provided nearly 235 hours of unfiltered CCD photometry. Table 1 list the participants in the study and Figure 1 depicts the light curve for IP Pegasi from the combined data sets. Even though observers used a variety of cameras and instruments at widely separated sites, the data sets combine very well as illustrated in Figure 2. Typical residual scatter between simultaneous data sets is on the order of 1 to 2 % after systematic trends have been removed.
| Observer and Site | Aperture (m) | Detector | N (hrs) |
| Cook, CBA_California | 0.44 | TI 245 | 27.1 |
| Harvey, CBA_West | 0.36 | KAF-1600 | 20.8 |
| Fried, CBA_Braeside | 0.41 | SITE 512 | 33.6 |
| Martin, CBA_Alberta (TKUCO) | 0.32 | TI 245 | 95.9 |
| Anderson, CBA_Alberta (Anderson) | 0.44 | TI 245 | 6.1 |
| Skillman, CBA_East | 0.66 | KAF-1600 | 19.8 |
| Van Munster, CBA Belgium | 0.35 | KAF-400 | 28.5 |
Figure 1. The CBA light curve for IP Pegasi during the fall 1999 campaign.
Figure 2. Light curve for IP Pegasi on October 14, 1999 showing the combination of 3 data sets from The King's University College Observatory and the Anderson Observatory (BA Alberta) and CBA West. Both CBA Alberta data sets were combined "as is" and a small systematic offset of 0.025 mag was applied to the CBA West data. The fit between the sets is excellent and residual scatter is less than 2%.
3. PHOTOMETRY
The photometry obtained for IP Pegasi was analyzed in two separate parts; those data acquired during quiescence and those obtained during outburst. Standard Fourier and Phase Dispersion Minimization (PDM) techniques were applied. As well, as a check on the consistency of the data sets, PDM and Fourier analysis was done on the individual data sets supplied by each observer in addition to the combined data from all observers.
3.1 IP Pegasi in Quiescence
Figure 3. shows a typical light curve for IP Pegasi during its quiet state. The light curve is dominated by a bright orbital hump of approximately 0.8 mag occurring at phase 0.85 (phased 0 at mid eclipse) and a deep eclipse. Table 2 summarizes the results of period analysis carried out on this data and Figure 4 presents Fourier power spectra for individual and combined data sets. The power spectra presented show peak power shifted into the second harmonic - an artifact produced by the presence of the bright orbital hump and deep eclipse and a fundamental period of 0.1582033 days. Figure 5 shows the power spectrum after the removal of the the fundamental indicates that no significant residual signal remains.
Figure 3. Light curve for IP Pegasi in quiet state on JD 2451497 (R. Fried, CBA Braeside). The prominent orbital hump is maximum at f=0.85 and presumably indicates the location of the bright spot on the accretion disk. The light curve is phased with respect to epoch JD 2451497.67205 and period 0.1582033 d . Phase 0 is set at mid-eclipse.
Table 2. Period analysis of IP Pegasi during quiescence.
| Observer | Period (d) |
| CBA Braeside (R. Fried) | 0.1582138 |
| CBA East (D. Skillman) | 0.1582050 |
| CBA Alberta (Martin & Anderson) | 0.1582175 |
| CBA California (Cook) | 0.1582183 |
| Combined data sets | 0.1582033 |
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Figure 4. Power spectra for data sets obtained by collaborating CBA observers (a-d) and the power spectrum from the combined, quiet state data for IP Pegasi collected during the Fall 1999 campaign.
Figure 5. Residual power spectrum (after removal of signal at fo = 6.32098 c/d) for IP Pegasi in quiesecence. No significant signal remains.