ATLAS-Teide Detects Centaur (60558) 174P/Echeclus in Ongoing Outburst

ATel #17817; J. Licandro (IAC, ULL), V. Kuksenko (UCB), Miquel Serra-Ricart, Miguel R. Alarcon (Light Bridges, IAC, ULL), P. Nichita (IAC, ULL), J. Tonry, L. Denneau, (IfA, University of Hawaii)
on 27 May 2026; 13:28 UT
Credential Certification: Javier Licandro (jlicandr@iac.es)

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We report that Centaur 174P/Echeclus has been detected in outburst in four 30s images obtained on 2026 May 11.9 UTC with the 2nd module of the ATLAS-Teide instrument (Licandro et al. 2025, EPSC-DPS2025-538, 10.5194/epsc-dps2025-538) installed at Teide Observatory (Tenerife, Spain). Echeclus was detected unexpectedly bright at magnitude 18.28 +/- 0.07. When observed it was at r = 14.042 and Delta = 14.326 au, where r and Delta are the heliocentric and geocentric distances respectively and a phase angle of 3.917 deg. If it were inactive, a brightness of V ~ 21 mag is expected given its absolute magnitude Hv = 9.97 +/- 0.03 (Pereira et al., 2023, MNRAS, 527(2), 3624). That means that Echeclus was > 13-times brighter than expected, meaning that it is in an active phase. No coma is detected above the noise level of the ATLAS images. An image produced by stacking the 4 ATLAS ones and centered on Echeclus is included. Such activity is not surprising for this object. This Centaur has displayed recurrent cometary outbursts of varying intensity, the most notable being a ~7 mag brightening in late 2005 at 13 au (Choi et al. 2006, CBET, 355,1). Subsequent outbursts were recorded in 2011 (~3 mag outburst, Jaeger et al., 2011, IAU Circ., 9213, 2), 2016 (~3 mag brightening, Miles, 2016, CBET, 4313), 2017 (~4 mag event post-perihelion, James, 2018, J. Br. Astron. Assoc., 128, 51). In all cases the object showed an extended coma. ATLAS-Teide is an array of 16 RASA11 telescopes (see Licandro, J. et al. 2023, 10.48550/arXiv.2302.07954 for details) equipped with QHY600PRO cameras, based on sCMOS sensors Sony IMX455 (Alarcon, M. R., et al. 2023, PASP, 135, 055001). Images are obtained using a Luminance (UV/IR cut) filter. ATLAS-Teide is the 5th unit of the ATLAS survey (Tonry, J.L., et al. 2018, PASP 130, 988, 064505 , see http://www.fallingstar.com for more information). All frames were bias-subtracted and flat-fielded following standard procedures. Point-source photometry was performed with a GPU-accelerated pipeline using PSF-matched detection and S/N-driven aperture photometry with PSF-based aperture corrections. Field stars were matched to Pan-STARRS DR1 to derive per-image photometric zero-points.

ATLAS-Teide image of Echeclus obtained on 2026 May 11.9 UTC.