Dear colleagues, ATLAS26dqo (aka TCP J16163603+4452289) was discovered by the ATLAS survey (J. Tonry et al.) on 2026 Mar 31.5 at mag 18.8. The object subsequently reached a peak of mag 14.0. The quiescent counterpart is a 22.8 g mag star, implying an outburst amplitude of ~9 mag. I have completed the analysis of my unfiltered CCD time-series observations of ATLAS26dqo, obtained on 2026 Apr 14/15 (CBA Belgium Observatory), and Apr 15/16 (CBA Extremadura Observatory, Spain). The data were acquired under mostly clear skies with 0.40-m telescopes. Key findings: * Superhump evolution: the Apr 14/15 light curve shows the emergence of Stage A superhumps with an amplitude of 0.07 mag. By Apr 15/16, the system transitioned into fully developed Stage B common superhumps with an amplitude of 0.14 mag. Note that I observed this object on multiple nights before Apr 15/16, but no obvious modulations were seen. * Period analysis: using multiple methods (ANOVA, Lomb-Scargle, Generalized-Lomb-Scargle and PDM via Peranso 3.1), I derive a combined superhump period of 0.0608 +/- 0.0004d for the night of Apr 15/16. * Magnitude: the object was measured at mag CV = 15.5 on Apr 15th. Conclusion: The extreme outburst amplitude (almost 9 mag) and the remarkably long delay (~15 days) between initial discovery and the onset of common superhumps strongly confirm that ATLAS26dqo is a new WZ Sge-type dwarf nova. Image calibration and photometry were carried out using Phoranso, which enabled simultaneous photometry of additional variable stars in the same field of view. Continued monitoring is strongly encouraged to study the superhump profile and evolution. I will submit my observations to AAVSO, CBA and VSNET for further analysis. With kind regards, Tonny --- Tonny Vanmunster CBA Belgium Observatory CBA Extremadura Observatory http://www.cbabelgium.co <http://www.cbabelgium.com/> m PERANSO : The Light Curve and Period Analysis Software http://www.peranso.co <http://www.peranso.com/> m PHORANSO: Photometric Reduction and Analysis Software http://www.phoranso.com <http://www.phoranso.com/>
Dear Tonny, Could you provide me a finder chart? I think I found the object in right position, but I am not sure, because when I performed photometry - it is at CV: 16-17 mag (large uncertainities) on April 17th (last night). I just wanted to make sure this is the right object. Thank you in advance, Weronika Skrobacz On Fri, 17 Apr 2026 at 01:48, tonny.vanmunster--- via vsnet-alert < vsnet-alert@ooruri.kusastro.kyoto-u.ac.jp> wrote:
Dear colleagues,
ATLAS26dqo (aka TCP J16163603+4452289) was discovered by the ATLAS survey (J. Tonry et al.) on 2026 Mar 31.5 at mag 18.8. The object subsequently reached a peak of mag 14.0. The quiescent counterpart is a 22.8 g mag star, implying an outburst amplitude of ~9 mag.
I have completed the analysis of my unfiltered CCD time-series observations of ATLAS26dqo, obtained on 2026 Apr 14/15 (CBA Belgium Observatory), and Apr 15/16 (CBA Extremadura Observatory, Spain). The data were acquired under mostly clear skies with 0.40-m telescopes.
Key findings:
* Superhump evolution: the Apr 14/15 light curve shows the emergence of Stage A superhumps with an amplitude of 0.07 mag. By Apr 15/16, the system transitioned into fully developed Stage B common superhumps with an amplitude of 0.14 mag. Note that I observed this object on multiple nights before Apr 15/16, but no obvious modulations were seen.
* Period analysis: using multiple methods (ANOVA, Lomb-Scargle, Generalized-Lomb-Scargle and PDM via Peranso 3.1), I derive a combined superhump period of 0.0608 +/- 0.0004d for the night of Apr 15/16.
* Magnitude: the object was measured at mag CV = 15.5 on Apr 15th.
Conclusion:
The extreme outburst amplitude (almost 9 mag) and the remarkably long delay (~15 days) between initial discovery and the onset of common superhumps strongly confirm that ATLAS26dqo is a new WZ Sge-type dwarf nova.
Image calibration and photometry were carried out using Phoranso, which enabled simultaneous photometry of additional variable stars in the same field of view.
Continued monitoring is strongly encouraged to study the superhump profile and evolution.
I will submit my observations to AAVSO, CBA and VSNET for further analysis.
With kind regards,
Tonny
---
Tonny Vanmunster
CBA Belgium Observatory
CBA Extremadura Observatory
http://www.cbabelgium.co <http://www.cbabelgium.com/> m
PERANSO : The Light Curve and Period Analysis Software
http://www.peranso.co <http://www.peranso.com/> m
PHORANSO: Photometric Reduction and Analysis Software
Dear Weronika I’ve attached a finder chart for ATLAS26dqo. In it, the variable is circled in magenta. I used the red-circled stars as Reference Stars in my photometry software Phoranso, and the cyan-circled star as the Check star. Best regards Tonny From: Skraczek <skraczekastro@gmail.com> Sent: Saturday, April 18, 2026 9:42 AM To: tonny.vanmunster@gmail.com Cc: cbastro-chat@googlegroups.com; Kenta TAGUCHI <kentagch@kusastro.kyoto-u.ac.jp>; ALERT, VSNET <vsnet-alert@ooruri.kusastro.kyoto-u.ac.jp>; Taichi Kato <tkato@kusastro.kyoto-u.ac.jp>; vsnet-campaign-dn@ooruri.kusastro.kyoto-u.ac.jp; vsnet-newvar@yahoogroups.com; 反保雄介 <tampo@kusastro.kyoto-u.ac.jp> Subject: Re: [vsnet-alert 28162] ATLAS26dqo: new WZ Sge-type dwarf nova Dear Tonny, Could you provide me a finder chart? I think I found the object in right position, but I am not sure, because when I performed photometry - it is at CV: 16-17 mag (large uncertainities) on April 17th (last night). I just wanted to make sure this is the right object. Thank you in advance, Weronika Skrobacz On Fri, 17 Apr 2026 at 01:48, tonny.vanmunster--- via vsnet-alert <vsnet-alert@ooruri.kusastro.kyoto-u.ac.jp <mailto:vsnet-alert@ooruri.kusastro.kyoto-u.ac.jp> > wrote: Dear colleagues, ATLAS26dqo (aka TCP J16163603+4452289) was discovered by the ATLAS survey (J. Tonry et al.) on 2026 Mar 31.5 at mag 18.8. The object subsequently reached a peak of mag 14.0. The quiescent counterpart is a 22.8 g mag star, implying an outburst amplitude of ~9 mag. I have completed the analysis of my unfiltered CCD time-series observations of ATLAS26dqo, obtained on 2026 Apr 14/15 (CBA Belgium Observatory), and Apr 15/16 (CBA Extremadura Observatory, Spain). The data were acquired under mostly clear skies with 0.40-m telescopes. Key findings: * Superhump evolution: the Apr 14/15 light curve shows the emergence of Stage A superhumps with an amplitude of 0.07 mag. By Apr 15/16, the system transitioned into fully developed Stage B common superhumps with an amplitude of 0.14 mag. Note that I observed this object on multiple nights before Apr 15/16, but no obvious modulations were seen. * Period analysis: using multiple methods (ANOVA, Lomb-Scargle, Generalized-Lomb-Scargle and PDM via Peranso 3.1), I derive a combined superhump period of 0.0608 +/- 0.0004d for the night of Apr 15/16. * Magnitude: the object was measured at mag CV = 15.5 on Apr 15th. Conclusion: The extreme outburst amplitude (almost 9 mag) and the remarkably long delay (~15 days) between initial discovery and the onset of common superhumps strongly confirm that ATLAS26dqo is a new WZ Sge-type dwarf nova. Image calibration and photometry were carried out using Phoranso, which enabled simultaneous photometry of additional variable stars in the same field of view. Continued monitoring is strongly encouraged to study the superhump profile and evolution. I will submit my observations to AAVSO, CBA and VSNET for further analysis. With kind regards, Tonny --- Tonny Vanmunster CBA Belgium Observatory CBA Extremadura Observatory http://www.cbabelgium.co <http://www.cbabelgium.com/> m PERANSO : The Light Curve and Period Analysis Software http://www.peranso.co <http://www.peranso.com/> m PHORANSO: Photometric Reduction and Analysis Software http://www.phoranso.com <http://www.phoranso.com/>
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Skraczek -
tonny.vanmunster＠gmail.com