Strong jet activity observed on comet C/2025 A6 (Lemmon) with the Two-Meter Twin Telescope

ATel #17450; M. Serra-Ricart (Light Bridges, IAC, ULL), J. Licandro (IAC, ULL), M. R. Alarcon (IAC, ULL)
on 21 Oct 2025; 22:02 UT
Credential Certification: Miquel Serra-Ricart (mserra@iac.es)

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Comet C/2025 A6 (Lemmon) was extensively monitored over 22 nights between 2025 September 15 and October 12 using the imaging capabilities of both the Two-Meter Twin Telescope (TTT) and the Transient Survey Telescope (TST). The TST, a 1-meter telescope located at the Observatorio del Teide (OT, Tenerife, Spain), is equipped with FERVOR-L, a 14304 × 10748 Sony IMX411 BSI sCMOS sensor providing a pixel scale of 0.60 arcsec pix-1 and an impressive field of view (FoV) of 2.4 × 1.8 degrees. For the study of jet structures, the TTT3 telescope was employed. TTT3 is a 2-meter f/6 Ritchey–Chrétien telescope, currently in its commissioning phase. Images were obtained with COLORS, a 2k × 2k camera mounted at the Nasmyth 2 focus, equipped with a back-illuminated BEX2-DD CCD sensor, resulting in a field of view of 7.85 × 7.85 arcsec and a plate scale of 0.23 arcsec pix-1. Comet Lemmon exhibits an exceptionally active nucleus, characterized by a large coma and multiple jet structures. We report the detection of several bright jets in visible-light (Lum filter) images obtained during the night of 2025 September 29–30. Between 04:57 and 06:01 UT, a total of 299 individual 5-second Lum-band exposures were acquired and co-added after compensating for the comet’s apparent motion and centering on its optocenter. A Laplace-filtered image of Lemmon’s central coma, processed following the method described by Serra-Ricart & Licandro (2015, ApJ, 814, 49), reveals two large spiral jets (likely dust jets, labeled A and B) extending toward the NE and SW, respectively, in the sky plane (sunward direction). Tail streamers are also visible, oriented approximately in the antisolar direction, along with additional fainter jets. The filtered image includes the projected velocity vector of the comet (blue arrow), the antisolar direction (yellow arrow), as well as the image orientation and distance scale. The cometary optocenter is marked with red lines. TTT nd TST are operated by Light Bridges in Tenerife, Canary Islands (Spain). The observation time rights (DTO) used for this research were consumed in the PEI ’PLANETIX25’. This research used storage and computing capacity in ASTRO POC’s EDGE computing center at Tenerife under the form of Indefeasible Computer Rights (ICR). Color image of C/2025 A6 (Lemmon) https://drive.google.com/file/d/1piAKHcOSfcvA1rukyVImaMzx7JGFAPIQ/view?usp=drive_link Jet image of C/2025 A6 (Lemmon) https://drive.google.com/file/d/1mF7z_iB8J0ZB6vIx2evIiVee30FJNP_e/view?usp=sharing Combined image https://drive.google.com/file/d/1S1-OO8uOLawX7OUEJ_ZUZhgJWRUA4-CG/view?usp=drive_link

Combined image