Extremely rare Superoutburst of RZ Leo

(CCD image taken at Kyoto University by R. Ishioka, M. Uemura, H. Iwamatsu, T. Kato, and K. Matsumoto)

(Finding chart of RZ Leo)

Superhumps!

(Phase-averaged superhump light curve on Dec. 22, taken at Kyoto University)

(Fully grown superhumps on Dec. 23, taken Kyoto University and S. Kiyota)

(Further evolution of superhumps on Dec. 26, taken Kyoto University and S. Kiyota)

(Further evolution of superhumps on Jan. 3, taken Kyoto University and S. Kiyota)

Outburst detection

(vsnet-alert 5437)

RZ Leo is in outburst at mag. 12.1 using the RASNZ chart.

001220.662    12.1

Regards,
Rod Stubbings

(vsnet-alert 5445)

RZ Leo outburst confirmed by Kinnunen

   [vsnet-obs 31246]
tells that the rare outburst of RZ Leo has been
confirmed by Kinnunen, at mv=12.2 on Dec. 21.21 UT.  The object had
not significantly faded!

Regards,
Taichi Kato

(vsnet-campaign-dn 327)

  YYYYMMDD(UT)   mag  observer
  20001207.165  <140  (P. A. Dubovsky)
  20001209.728  <120  (R. Stubbings)
  20001209.856  <136  (H. Maehara)
  20001212.839  <134  (H. Maehara)
  20001220.662   121  (R. Stubbings)
  20001220.699   121  (R. Stubbings)
  20001220.719   122  (R. Stubbings)
  20001221.210   122  (T. Kinnunen)
  20001221.222   126  (E. Muyllaert)

Superhump detection

(vsnet-alert 5446)

Dear colleagues,

I just concluded a CCD photometry session on RZ Leo, lasting for 4.1 hours, using the 0.35-m f/6.3 telescope at CBA Belgium Observatory [2000, December 20/21]. All FITS images were acquired with an ST-7 CCD camera without filters, and were instanteneously processed and reduced (PSF photometry). The resulting real-time light curve clearly shows the presence of a 0.20 mag modulation, to be attributed to superhumps. A first rough estimate of the superhump period yields a value of 0.079 d.

The above observations thus establish RZ Leo as yet another new member of the UGSU type of cataclysmic variables!

Further high-speed photometry is highly recommended during the present outburst of this interesting object !!

Best regards,

Tonny Vanmunster
CBA Belgium Observatory

(vsnet-alert 5448)

Re: [vsnet-campaign 594] RZ Leo outburst

>     We started tonight CCD time-series observation of RZ Leo on 18:00 (UT).
> We are planning over three hours run. 
> The object has been still bright.

The analysis of the data clearly shows 0.15-mag superhumps. Preliminary analysis gives a period around 0.076-0.077 d, which looks slightly shorter than that reported by Vanmunster. More details will be reported later by Ishioka-san et al.

Regards,
R. Ishioka, M. Uemura, H. Iwamatsu, T. Kato, K. Matsumoto
at Kyoto University
On behalf of the VSNET Collaboration team

Early superhump

(vsnet-campaign 599)
(see also, vsnet-campaign 598, vsnet-campaign 600, vsnet-campaign-dn 341, vsnet-campaign 602)

RZ Leo superhumps: early superhumps?

Dear Colleagues,

We must remind that the best superhump period (P=0.0762 d) is extraordinally close to the photometric period (0.0756 +/- 0.0012 d, Mennieckent et al., 1999, Astron. Astrophys. 352, 239). The values may even regarded to "agree" within their errors.

The observed hump profile is also peculiar in contrast to "usual" superhumps in SU UMa stars. The humps show a complex structure, similar to "early superhumps" observed in other WZ Sge-type stars (AL Com, EG Cnc, HV Vir).

These findings may indicate that we are observing the very early stage of a WZ Sge-type dwarf nova, which commonly show complex "superhumps" whose period is close to the orbital period (see the VSNET AL Com page and paper for reference).

This feature may quickly decay, as in other WZ Sge-type stars, or develop into more distinct superhumps within several days. Intensive observations at this extremely rarely met stage are of utmost importance.

Let's join this Christmas and New Millenium world-wide campaign!

Regards,
R. Ishioka, M. Uemura, H. Iwamatsu, T. Kato, K. Matsumoto
at Kyoto University
On behalf of the VSNET Collaboration team

And then, "true" superhump evolved

(vsnet-campaign 603)
(see also, vsnet-campaign 604 vsnet-campaign 606 vsnet-campaign 609)

Dear Colleagues,

The Dec. 23 data at Kyoto (Kyoto team) and Tsukuba (S. Kiyota) have revealed that fully grown "true" superhumps with an amplitude of ~0.3 mag have finally evolved. The best period determined from the data is 0.0808 d, which is 6.0% longer than the period of the "early superhumps" by the Kyoto team (P=0.0762, vsnet-alert 5451, 5452), or 7.0% longer than Vanmunster's period (P=0.0755, vsnet-alert 5454). This finding perfectly qualifies the variation as being genuine superhumps, which had just begun to develop. The relatively rapid fading trend in the early epoch has apparently slowed down as the appearance of genuine superhumps.

We have also received earlier data from Gianluca Masi, and we hope we will be able to refine the above values by incorporating all the data.

Data to the VSNET Collaboration team RZ Leo project should be sent to Ishioka-san (ishioka@kusastro.kyoto-u.ac.jp the campaign coordinator) with a cc: to me, or more directly to the vsnet-campaign-data list (vsnet-campaign-data@kusastro.kyoto-u.ac.jp, see [vsnet-campaign-data 1] for the description of the purpose and usage of the list).

Looking forward to your successful observations!

Regards,
The VSNET Collaboration team

Historical record of RZ Leo outburst

(vsnet-alert 5447)

   Amended list of previous outbursts:

   1918.03.13   10.5p   Wolf (discovery)
   1935.03.25   12:p    uncertain, see IBVS 2714
   1952.04.17   13?p    uncertain, see IBVS 2714
   1976.03.03   13:p    uncertain, see IBVS 2714
   1984.12.29   12.9v   Ducoty (IAUC 4026, 4027), long-lasting
   1987.11.27   12.3v   Lubbock (IAUC 4504)
   1988.04.20   13.8v   Miroyama (single sighting)
   1989.03.10   13.6-13.2v Namuri detected on the rise (IAUC 4757)
                        12.8v at peak (from IAUC)
                        Koshiro reports the outburst lasted for more than
                        five days
   1990.10.27   12.8v   Dyck (confirmed?)

What are dwarf novae and WZ Sge stars?

Dwarf novae are close binary systems which experience repetitive outbursts. Intervals of these outbursts are known to be typically several weeks or several months, however there are some systems which have very long intervals over ten years. They are called as "WZ Sge-type" or TOADs, and the nature of these system has poorly been studied. WZ Sge-type stars form a sub-group of SU UMa-type dwarf novae which show two distinct outbursts, i.e. normal and superoutburst. During the superoutburst, we can see periodic modulations called "superhumps" which can give us a number of clues for the system and the mechanism.

Observation guide for superhumps

Superoutbursts generally last for about two weeks. Follow-up observations are very important to study this system. We would encourage all observers to closely follow the present outburst, using CCD or other photometry device, time-resolved spectroscopy to detect the irradiated secondary, and multiwavelength observations. The object is naturally chosen as the top-priority target for the VSNET Collaboration team.

For CCD observations, we recommend to use 10-30 sec integration times, use unfiltered CCD (unless you have a large telescope), and continue grabbing as many frames as possible (until dawn). Take appropriate dark and flat field frames for accurate photometry. Ensure several nearby stars (of 11-13 mag) are always within the same field. Avoid saturation of both target and comparison stars. Do not use ABG. Simple aperture photometry is enough for extracting variation. In order to obtain good time-series photometry, please keep your PC's clock adjusted at least to 1 sec (or hopefully less than this). Please ensure excat exposure times are recorded in your images (please confirm whether the recorded times represent the start, mid or end exposure; if this is not certain, one may better independently record start exposure times manually). When you report the results, reduce these times to mid-exposure times. If your CCD is equipped with on-chip binning, choose the binning so that 1 pixel corresponds to ~2 arcsec (even larger pixel size is allowed depending on the actual seeing size). Since the field is not crowded, high spatial resolution is not necessary.