Superoutburst of KS UMa in 2003 February


(vsnet-outburst 5229)

Star             UT            Mag
UMAKS     Feb 18.840     12.7    Seq. AAVSO


Eddy Muyllaert
Oostende, Belgium

(vsnet-outburst 5230)

Outburst of KS UMa

Feb 18.931  12.9

Gary Poyner

(vsnet-campaign-dn 3447)

KS UMa likely superoutburst

As reported by Eddy Muyllaert and Gary Poyner, the SU UMa-type dwarf nova KS UMa is undergoing a likely superoutburst. The superhump period is 0.06955 d. Because of the excellent visibility in this season, and because of the lack of the entire coverage of a superoutburst in the past, we would encourage further time-series observations during the current outburst. With this outburst, we hope we will be able to get a complete picture of superhump evolution, late stage phenomenon, and on the existence of a rebrightening. If you have already set up for BC UMa, the same observing technique applies. Watch for a rebrightening of BC UMa and observe superhumps in KS UMa!

Early Observations

(vsnet-campaign-dn 3449)

Dear colleagues,

Last night (2003, Feb 18/19), I conducted an unfiltered CCD observing campaign on KS UMa at CBA Belgium Observatory, during 3.4 hours, under very good atmospheric conditions. A quick inspection of the resulting light curve shows no obvious (large-amplitude) modulations. The conclusion therefore is that we are either observing a normal outburst of KS UMa, or that superhumps still have to develop (early outburst stage).

I will make my observations and the results of a more detailed analysis available later today, and will put the light curve on my web site.

Since the weather forecast is positive, I expect to start another observing session on KS UMa tonight. In fact, this will be my 8th clear night on a row - an unprecedented Belgian experience, especially in the month of February !

Kind regards,
Tonny Vanmunster
CBA Belgium Observatory

(vsnet-campaign-dn 3454)

KS UMa observation from Tonny Vanmunster and Nakajima-san

Dear Colleagues,

We have received KS UMa observations from Tonny Vanmunster (as Tonny already reported) and from Nakajima-san. The object was also successfully observed by the Kyoto team (two nights, including the initial day of the outburst) and by Torii-san (RIKEN).

The resultant light curve by Tonny is what he already described. Nakajima-san's light curve lasy night, however, seems to show a weak (~0.05 mag) signal, which may be attributed to early-stage superhumps. The present outburst thus likely presents an excellent opprotunity to follow the development of superhumps in KS UMa. We may expect that the modulations may have become stronger in the Nyrola observations.

Taichi Kato
VSNET Collaboration team


(vsnet-campaign-dn 3459)

Dear colleagues,

As I reported in vsnet-campaign-dn 3455, last night (2003, February 19/20) I was able to monitor KS UMa for 4.6 hours under good conditions, at CBA Belgium Observatory.

The resulting light curve (see is telling a completely different story compared to yesterday, with strong superhumps being present, and therefore classifying the present outburst as a genuine superoutburst.

Using the PDM technique, I derived a superhump period of 0.0719 +/- 0.0010 d. This Psh value is slightly higher than the value of 0.0697 d that I reported in 1998 (CVC 161, vsnet-alert 1448; CVC 162, vsnet-alert 1450), at the moment I detected the UGSU-type nature of KS UMa. D. Nogami (vsnet-alert 1452) then also reported a Psh value of 0.069 d.

Follow-up observations are encouraged to precisely determine the Psh value and evolution over time.

By the way : it's again a very clear night over Belgium, and KS UMa will be on my 'menu' later tonight. I have lost track counting the number of successive clear nights I'm having now, but this is just fantastic. Must be like doing astronomy from Arizona or New Mexico :-).

Kind regards,
Tonny Vanmunster
CBA Belgium Observatory
email :
website :

(Averaged superhump profile of KS UMa)

(vsnet-campaign-dn 3460)

KS UMa: full development of superhumps: unusual superhump period!

Dear Colleagues,

We have received new data from Tonny Vanmunster and the Nyrola team (Arto Oksanen). We have also received the most recent, fantastic data from Nakajima-san, which covered full 6 superhump cycles. The usual observation and analysis of Kyoto team and Torii-san (RIKEN) are also steadily in progress.

From these data, the develpment of the superhumps took place on Feb. 19, as already reported. Several hours later, the Nyrola team recorded the growing signal. The amplitude of the superhumps reached 0.25 mag, as Tonny reported. On Feb. 20 later, the amplitude has fully grown to 0.30 mag.

From the Feb. 20 observations, the resultant superhump period is 0.07068(7) d, which is substantially longer than the perviously reported periods (see also Tonny's summary in vsnet-campaign-dn 3459). It may be possible that KS UMa is experiencing a stage of rapid evolution of superhump periods, as we have seen in UV Gem early this year. Up to now, such dramatic period changes of the superhumps (except WZ Sge-type early superhumps and trasition in T Leo, Kato (1997) PASJ 49, 583) during the early superoutburst stage have been confined to long-period systems, or systems close to the lower edge of the period gap. If a similar period change (rapid period decrease) is confirmed in KS UMa, this object would become the first object which shows similar evolution of superhump periods as in long-period systems. Further detailed, long coverage is naturally of utmost importance!

Taichi Kato
VSNET Collaboration team

(vsnet-campaign-dn 3467)

KS UMa: superhumps update

Dear Colleagues,

We have received new data from Tonny Vanmunster (two nights, as already reported by Tonny) and the Nyrola team. New data by the Kyoto team and Torii-san (RIKEN) have been also added.

The resultant mean superhump period is 0.07026(2) d. This period (most likely progressively updated) is now the best determined superhump period of KS UMa.

We have now detected a significant period change. The rate of change dot(P)/P is around -3*10(^4). Since the baseline is still short, we must wait for another days to confirm this trend. If confirmed, this negative period derivative is one of the most pronounced among moderate-period SU UMa-type dwarf novae. This might partly resolve the inconsistency of the superhumps periods determined on different occasions. Except for UV Gem and recently discovered objects such as V877 Ara and KK Tel, there is a tendency that the dot(P)/P makes a minimum around P=0.075 d (Kato et al. (2002) PASJ 54, 1017). KS UMa would be another, but possibly more striking, object following this trend. Further observations to completely follow the superhump evolution are encouraged.

Taichi Kato
VSNET Collaboration team

Background Information

KS UMa = SBS 1017+533

CVs from SBS survey

In a recent article of Astrophysics 40, 101 (1997, original in Astrofizika 40, 153, 1997), S. K. Balayan presents spectral classification of SBS (Second Byurakan Sky Survey). 10 CVs were idetified. Seven of them are already well-known CVs or related systems.

   BH Lyn = SBS 0818+512
   SW UMa = SBS 0833+536
   BZ UMa = SBS 0849+580
   ER UMa = SBS 0943+521, position different, probably due to misidentification
   PG 1002+506 = SBS 1002+505
   DW UMa = SBS 1030+590
   BE UMa = SBS 1155+492

   Three remaining new CVs are

                       (2000.0)        mpg
  SBS 0755+600   075926.60 +595349.98  17.5
  SBS 1017+533   102030    +530207     17.0
  SBS 1150+599   115324.88 +593955.15  17.5
Identifications of other objects suggest the accuracy of the coordinates is not significantly better than 1 arcsec.

Among them, SBS 0755+600 is pretty close to a USNO star at 075926.44 +595351.3, r=15.5, b=16.0, which may be identical with the SBS object caught in outburst. Located close to SBS 1017+533 a ROSAT X-ray source, which may be identified with a USNO star at 102026.65 +530432.6, r=15.6, b=16.5, but the connection with the SBS object is not certain.

Monitoring for these objects may be meaningful.

Taichi Kato

(vsnet-alert 1441)

Peter Garnavich has kindly informed the outburst of recently discovered cataclysmic variable, SBS 1017+533. Observations are highly encouraged.

It has been rather cloudy at the MMT so I have been getting spectra of the new CVs from the SBS catalog.

SBS 0755+600 is a beautiful CV with broad Balmer lines and some
             HeI. No HeII 4686 is seen.

SBS 1017+533 The coordinates were not good enough to find a single
             star so I went to USNO at 10:20:26.65 +53:04:32.6 (2000)
             and I was suprised to find a 13th magnitude star there.
             It is in outburst (Jan 27.5 UT). The spectrum shows
             a CV in outburst with broad Balmer absorption except
             for Halpha which is in weak emission.

SBS 1150+599 has strong Balmer lines plus HeII 4686, but they are
             unresolved and the Balmer decrement is not that seen
             in CVs. It also has a hot blue continuum. My guess is
             that this is a young planetary nebula
             or maybe a symbiotic system.

Peter Garnavich

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