[vsnet-outburst 22944] ATLAS18zfu = AT 2018imn: possible new SU UMa type dwarf nova

Sat Nov 17 10:10:10 JST 2018

Dear colleagues,

I have just concluded the analysis of my 2018, Nov 16/17 unfiltered CCD photometry session of ATLAS18zfu. Observations were made at CBA Belgium Observatory,  using a 0.40-m f/10.0 telescope and STT-3200ME CCD camera, under very clear skies. 

The resulting light curve reveals the presence of a likely periodic, low amplitude signal, which might be attributed to developing superhumps. This is a very preliminary interpretation, and further observations are urgently needed to more precisely determine the full characteristics of this system. The measured amplitude of the signal is 0.06 mag. A period analysis using the ANOVA, Lomb-Scargle and PDM methods (Peranso), yields a combined superhump period of 0.085 +/- 0.003d.  The object was at mag 15.46 (CV) on Nov 16th.  

I calculated the False Alarm Probability (FAP) for the above period. This is a metric to express the  <mk:@MSITStore:F:\Program%20Files%20(x86)\Peranso\Peranso.chm::/period_significance2.htm> significance of a period. A False Alarm arises in period analysis techniques when incorrectly a period is found where none exists in reality. The lower the FAP for a given period P, the more likely P is a significant period. FAP values are expressed as a number between 0 and 1. As a rule of thumb : FAPs below 0.01 (1%) mostly indicate very secure periods, and those between 0.01 and 0.20 are far less certain. Anything above 0.20 mostly relates to an artifact, instead of a true period. I used a Fisher Randomization Test with 100 permutations in Peranso to calculate 2 complimentary False Alarm Probabilities for the above mentioned period P = 0.085d:  (1) FAP1 is the probability that there is no period in the dataset with value P, (2) FAP2 is the probability that the data contains a period different from P. Peranso returns a value of 0.001 for FAP1 and FAP2, hence indicating that the above period is rather secure. 

Observations will be sent to AAVSO, CBA and VSNET for further analysis. 

Best regards
Tonny

Tonny Vanmunster
CBA Belgium Observatory
CBA Extremadura Observatory
 <http://www.cbabelgium.com> www.cbabelgium.com

 <http://www.peranso.com> www.peranso.com

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