RevMexAA (Serie de Conferencias), 20, 259-259 (2004)

DWARF NOVA-LIKE OUTBURST OF SHORT-PERIOD INTERMEDIATE POLAR HT CAMELOPARDALIS

R. Ishioka^ and VSNET Collaboration Team

Our time-series photometric observations of 2002 11 a short outburst of HT Cam in 2001 strongly 12 - HT Cam outburst suggest that disk instabilities occurred during 13 - the outburst. 14 - HT Cam is a cataclysmic variable identified as 15 the optical counterpart of the hard X-ray source RX 16 J0757.0+6306, discovered during the ROSAT All- 17 Sky Survey. Tovmassian et al. (1998) suggested that 18 270 271 272 273 274 275 276 277 278 279 280 this object is an intermediate polar with a short­ HJD - 2452000 est orbital period of 80.92min and a spin period of 8.52min. However, the existence of dwarf nova-like Fig. 1. The light curve of the outburst in 2001. The outbursts and the short orbital period allowed an al­ crosses with error bars show average magnitude in 1 -hr ternative interpretation that it may be an SU UMa- bins of the time-series CCD observations. The filled cir­ type dwarf nova or WZ Sge-type stars (Tovmassian cles and small crosses show positive detections by visual et al. 1998). or snapshot CCD observations and the upper-limits of After its discovery, 6 outbursts were reported visual observations reported to VSNET. during 4 years. Considering the density of the ob­ 12 (0o> 14 servations and the shortness of the outbursts, and E 16 18 seeming regularity, the reccurence time of outbursts 2273.6 2273.8 2274 2274.2 2274.4 is about 150 d. This is quite typical among the dwarf HJD-2450000 novae. a b -0.1 J i $ The 6th outburst was detected by H. Itoh on 29 0.0 q December 2001, and we started the first time-series S’ 0.1 E observation 0.5 d after the outburst detection and c ' d i-0.1 succeeded in observing during the declining phase , i S i* , q 0.0 " 1 i “ ' ■ 1 J " 1'. . i T ' ; ’ of the short outburst. Figure 1 shows the outburst 0.1

light curve. The rising phase was missed, but the -1 0 1 2 -1 0 1 2 last quiescent observation reported to VSNET was phase performed within 1.5 d before the detection. Thus, the rising rate is faster than 3 mag d“ b Fig. 2. Averaged spin profiles during the declining phase. In the light curve of the declining phase of the The declining rate changed at HJD 2452274.0. outburst , we detected long-term modulations with to ~ 0.1 mag (b). It then gradually increased again a period of 86min and strong pulses with a period of during the rapidly declining phase (c,d). 8.6 min. Strong 8.6 min coherent pulses are white The discrepancy between the declining rates of dwarf spin pulses and we identified the 86 min period the total flux and the pulse flux strongly suggests as the orbital period. By detecting the spin period, that disk instabilities occurred during the outburst. we confirmed the IP classification of HT Cam. The Additionally, the regularity of the outbursts suggests rather short spin period indicates that the magnetic that the outbursts on HT Cam are caused by disk field of HT Cam is not very strong. instabilities starting at the outer disk edge. Figure 2 shows the average spin profiles of the data on December 30, after subtracting the longer REFERENCES time-scale modulations. At first the amplitude of Ishioka, R., Kato, T., Uemura, M., Billings, G. the spin pulse was ~ 0.2 mag (a), but it decrecised Mofikawa, K., et al. 2002, PASJ, 54, 581 ^Department of Astronomy, Graduate School of Science, Tovmassian, G. H., Greiner, J., Kroll, P., Szkody, P., Ma­ Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan (ishioka® son, P. A., et al. 1998, A&A, 335, 227 kusastro. kyoto- u. ac. j p).

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