KT Eri (Nova Eri 2009) on a steep rise toward record brightness and a new state

ATel #17125; U. Munari (INAF Padova), S. Dallaporta (ANS Collaboration), S. Shugarov (AISAS, Slovakia), and P. Golysheva (SAI MSU)
on 2 Apr 2025; 13:19 UT
Credential Certification: U. Munari (ulisse.munari@oapd.inaf.it)

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Nova Eri 2009 (KT Eri), is an He/N nova discovered by K. Itagaki on 2009 November 25.5 UT (CBET #2050), well past its optical maximum. Pre-discovery lightcurve was reconstructed by Hounsell et al. (2011, ApJ 724, 480) from satellite SMEI observations, highlighting a rapid rise in magnitude following the first detection on 2009 November 13.12 UT and a sharp maximum reached on 2009 November 14.67 UT, after which the nova immediately entered a rapid decline characterized by t(2) = 6.6 days. The nova, rather anomalous for its limited amplitude range, has been intensively observed over the whole electromagnetic range, and generally considered consistent with the properties of recurrent novae, even if no historic outburst has been found during searches in photographic plate archives (Jurdana-Sepic et al. 2012, A&A 537, A34).

We are intensively monitoring KT Eri since its return to quiescence in 2010. The 2010-2025 BVRI lightcurve recorded with ANS Collaboration telescope IR 0310 can be viewed here, while the U and R lightcurve collected with various telescopes located in Slovakia and Crimea is presented in this picture. The median brightness over 2010-2025 is U=14.38, B=15.24, V=14.99, R=14.77, and I=14.51, with KT Eri constantly varying in a chaotic more than periodic manner around these values, with an amplitude of several tenths of a magnitude and constant colors. The spectral appearance, regularly monitored with the Asiago 1.22m + B&C telescope, has consistently remained that of a hot source, with an intense Balmer continuum in emission, and strong HeI, HeII, and Balmer emission lines, with HeII 4686 being by far the strongest line at optical wavelengths (Munari et al. 2014, A&A 564, A76; Shugarov et al. 2024, arXiv 2411.19348).

The photometric appearance of KT Eri has recently significantly changed: the large and chaotic variability has disappeared and the object is since Oct 2024 on a smooth and constant rise at all wavelengths, breaking through record brightness since the 2009 outburst. Our last observation for 2025 March 23.785 UT reads B=14.221, V=13.985, R=13.856, and I=13.644. The change in behavior and the unprecedented bright state suggest that KT Eri may be undergoing transition to a new and different phase worth investigating.

Observations at other wavelengths are strongly encouraged, as well as continued monitoring when the object will re-emerge from the Solar conjunction it is currently entering.