## Discovery

Dear Colleagues,

Bill Worraker, Didcot UK, reports a bright (Supermax?) outburst of AK Cnc, which is part of the UK Nova Supernova patrol recurrent objects programme. The following positive observations were all made by Bill using a 26cm reflector...

Mar 07.892 UT   mv= <14.5  Poyner
09.001           12.8
09.021           12.8
09.038           12.7
09.060           12.8
09.082           12.8


The outburst was reported late, so confirmation has not yet been achieved.

The last reported outburst occured on April 08 1994, when it was seen - again by Bill - at mv=14.3.

Best regards,
Gary Poyner

## Steve Howell's comment

This star is a suspected Tremendous outburst amplitude dwarf novae (TOAD) and has NO known orbital period. Superhumps should appear and time series photometric observations will thus provide an orbital period (cf. IBVS 4043).

I encourage observers to attempt such observations. Spectroscopic observations would be useful as well. ref: ApJ 1995 439 337.

 Steve B. Howell
Planetary Science Institute, Astrophysics Group
620 N. 6th Ave.
Tucson, AZ 85705  USA
Phone (602) 622-6300
Fax (602) 622-8060
e-mail: howell@frankenstein.psi.edu


## Observations of superhumps by R. Mennickent

(vsnet-alter 78)

Dear Collegues:

I have observed 2 superhumps maxima in March 12, UT= 03:47 and 05:14, during the current supereruption of AK CnC. The first superhump is broad and the second one is narrow. Both have amplitude approx. 0.2 mag. in the V band. The broader superhump is characterized by a slow increase and a rapid decline of luminosity. I pretend to continue monitoring this star with thr 1.0 m telescope at Las Campanas Observatory, Chile, with different bandpasses during the next 4 nights, if weather continues good.

We plann to observe AK Cnc spectroscopically during March 20-24 from Beijing and Las Campanas (Mr. Xue-Bing WU has kindly offered to collaborate in a joint, coordinated campaign).

Ronald Mennickent
rmennick@buho.dpi.udec.cl

## The 1992 Superoutburst (IBVS paper)

AK Cnc was discovered by Morgenroth (1933), who classified it as a possible short-period variable star. After a long period of confusion, the object was identified as a dwarf nova (for a review, see Wenzel 1993). The peculiarity of this object was noted by Szkody and Howell (1992), who identified strong Balmer and helium emission lines and a red continuum in their spectrum, and estimated the quiescent $M_{\rm V}$ value between 10.4 and 11.9. The faintness of quiescent $M_{\rm V}$ and a large outburst amplitude (greater than 6 mag) make AK Cnc a good candidate for a TOAD (Tremendous Outburst Amplitude Dwarf Nova; Howell 1993). A search for a photometric period has been, however, remained unsuccessful (Howell et al. 1990).

On 1992 Jan. 13, the object was caught in its one of rare outbursts at mv=13.6 (Koshiro, private communication). We obtained a V-band CCD photometry of this star on three night between Jan. 17 and Jan. 22. The observations were carried out using a 60 cm reflector and a Thomson TH7882 chip (576x384 pixels) at Ouda Station, Department of Astronomy, Kyoto University (for a description of the instruments see Ohtani et al. 1992). The exposure time was between 30 and 60 s to avoid saturation from the strong moonlight. The frames were first corrected for standard de-biasing and flat fielding, and were then processed by a microcomputer-based automatic-aperture photometry package developed by the author. The differential magnitudes of the variables were determined using a local standard star (C$_1$: 08$^{\rm h}$ 55$^{\rm m}$ 15$^{\rm s}$.42 +11$^\circ$ 14' 53".8 (J2000.0), {\it V}=13.3), whose constancy was confirmed using a check star (C$_2$: 08$^{\rm h}$ 55$^{\rm m}$ 26$^{\rm s}$.05 +11$^\circ$ 20' 04".5 (J2000.0), {\it V}=15.1). Total number of useful frames was 1007.

The resultant overall light curve is shown in Fig. 1. The zero-point corresponds to {\it V}=13.3. A general trend of slow linear decline is evident. Superimposed with this decline, superhumps with an amplitude of 0.18 mag were detected on all nights. The star was thus for the first time identified as being an SU UMa-type dwarf nova.

A representative light curve is shown in Fig. 2; a large scatter in the light curve is caused by a high sky background due to the proximity of the object to the nearly full moon. A period analysis using the phase dispersion minimization (PDM) method (Stellingwerf 1978) implemented in the IRAF package after removing the steady decline yielded the best estimate of the superhump period of 0.06735 +/- 0.00005 day. A light curve folded by this period is shown in Fig. 3. Each point represents an average of 0.05 phase bin and its standard error. This clearly demonstrates all the characteristics of fully grown superhumps: a rather steep rise to maximum, slower decline, and a secondary broader maximum around superhump phase 0.4 -- 0.5. The superhump makes AK Cnc a member of short orbital-period SU UMa-type dwarf novae. This picture is in good agreement with the spectroscopic features described by Szkody and Howell (1992).

The outburst characteristics of this dwarf nova is still uncertain. Wenzel (1993) gives five outburst records from Sonneberg plates. The second one in his table (1993 March 8 -- 15) is clearly a superoutburst. Further monitoring for outbursts of this dwarf nova is encouraged in order to determine its true outburst frequency and number ratio of super- and normal outbursts, both of which would also be good indicators for discriminating TOADs from other dwarf novae.

Taichi Kato

The author is grateful to Masami Koshiro (VSOLJ) for notifying us of the outburst. Part of this work is supported by a Research Fellowship of the Japan Society for the Promotion of Science for Young Scientists.

References

Howell, S. B. 1993, in {\it Cataclysmic Variables and Related Physics}, ed O. Regev, G. Shaviv, Annals of the Israel Physical Society, Vol. 10, p.67.

Howell, S. B., Szkody, P., Kreidl, T. J., Mason, K. O., and Puchnarewicz, E. M. 1990, {\it Publ. Astron. Soc. Pacific}, {\bf 102}, 758.

Morgenroth, O. 1933, {\it Astron. Nachricht.}, {\bf 249}, 383.

Ohtani H., Uesugi A., Tomita Y., Yoshida M., Kosugi G., Noumaru J., Araya S., Ohta K. et al. 1992, {\it Memoirs of the Faculty of Science, Kyoto University, Series A of Physics, Astrophysics, Geophysics and Chemistry}, {\bf 38}, 167.

Szkody, P. and Howell, S. B. 1992, {\it Astrophys. J. Suppl.}, {\bf 537}, 547.

Wenzel, W. 1993, {\it IBVS}, No. 3921.