1eRASS J072044.9-402838: updated superhump period

With the observations from Josch Hambsch, the period of ordinary superhumps in 1eRASS J072044.9-402838 after 26 Oct is updated as 0.058048(7) d, although 1-d aliases are still possible. Some modulations exist before this date, which are likely growing superhumps.

Best regards, Yusuke

2025年11月4日(火) 10:29 Yusuke Tampo tampo@kusastro.kyoto-u.ac.jp:

1eRASS J072044.9-402838 = PNV J07204545-4028357 = ASASSN-25ee: new SU UMa-type dwarf nova, likely WZ Sge-type

1eRASS J072044.9-402838 was originally identified as a CV candidate in Rodriguez et al. (2025), G = 19.2 mag at ~267 pc, hence its absolute magnitude of ~12 mag. https://vsx.aavso.org/index.php?view=detail.top&oid=10868116 https://ui.adsabs.harvard.edu/abs/2025PASP..137a4201R/abstract

ASASSN and John Seach discovered its 2025 outburst, peaking at ~11.0 mag around 20th October. https://www.astronomy.ohio-state.edu/asassn/transients.html http://www.cbat.eps.harvard.edu/unconf/followups/J07204545-4028357.html

We, the SAAO team, obtained the time-resolved photometries and a snapshot spectrum of 1eRASS J072044.9-402838 on 3rd Nov. The light curve shows likely superhumps with a rough period of ~0.059 d. The spectrum shows Balmer absorption lines from the accretion disk and a superposed narrow emission component in Hα.

Hence, 1eRASS J072044.9-402838 is now confirmed as (at least) a SU UMa-type dwarf nova, and probably a WZ Sge-type dwarf nova, considering its large outburst amplitude, long outburst duration, and short superhump period.

Further time-resolved observations are encouraged to establish its superhump period and changes.

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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