Re: ASASSN-25dc; updated superhump period

Lesedi telescope, Josch Hambsh, and Berto Monard have reported further observations. Combining the AAVSO data of Peter Starr and William Goltz, I obtained the updated superhump period of 0.059442(7) d after the dip. The mean superhump amplitude is ~0.06 mag. Such a small superhump amplitude suggests that this system can be a period bouncer system.

Moreover, the ATLAS light curve shows a slow outburst rise between MJD 60860-60865, atypical of dwarf nova superoutbursts.

https://fallingstar-data.com/forcedphot/queue/3062125/

I encourage the continuous monitoring of ASASSN-25dc with time-resolved observations (currently ~13.5 mag). As the light curve after the peak brightness somewhat resembles EG Cnc, ASASSN-25dc may undergo some rebrightenings after the rapid decline.

Best regards,

Yusuke

2025年7月18日(金) 10:22 Yusuke Tampo <tampo@kusastro.kyoto-u.ac.jp>:

ASASSN-25dc; a new candidate of a WZ Sge-type dwarf nova with the double superoutburst

ASASSN-25dc was discovered by ASAS-SN on 2025-07-13.09 UTC at g=13.07. This outburst is also observed by ATLAS, o~15.2 mag on  2025-07-07.8 UTC and o~13.5 mag on 2025-07-10.9 UTC. The likely counterpart is Gaia DR3 6129070308813533568 with G~21.0 mag, hence the outburst amplitude is ~7.0 mag. 

This system underwent a short dip on 16-17th July, around 14.5 mag, and is now recovering from the dip.

Lesedi telescope at Sutherland, Josch Hambsh, and Berto Monard have reported the time-resolved observations of ASASSN-25dc. PDM analysis using the overall data yields a single-peaked modulation with a period of 0.05991(4) d and an amplitude of 0.03 mag. Combining the 1-mag dip feature on the light curve and short superhump period, ASASSN-25dc can be a similar system to double-superoutburst WZ Sge-type dwarf novae, especially the period-bouncer candidates ASASSN-15jd and ASASSN-16hg (see Kimura et al. 2016,2018).

https://arxiv.org/abs/1604.06344

https://arxiv.org/abs/1803.03179

The ongoing second outburst should show the evolution of ordinary superhumps. The hint of ordinary superhumps is seen in the observations on 17th July.  Further time-resolved observations are encouraged.

Best regards,

Yusuke

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South African Astronomical Observatory, Postdoc fellow

Yusuke TAMPO / 反保 雄介

EMAIL: tampo@kusastro.kyoto-u.ac.jp

ALT. EMAIL: yusuke@saao.ac.za

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South African Astronomical Observatory, Postdoc fellow

Yusuke TAMPO / 反保 雄介

EMAIL: tampo@kusastro.kyoto-u.ac.jp

ALT. EMAIL: yusuke@saao.ac.za

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