The Fast Nova Sge 2026 (V0488 Sge) from photospheric to nebular regime in four days

ATel #18021; Paolo Ochner (DFA UNIPD), Costantino Sigismondi (ICRANet Pescara and APRA Roma), Andrea Reguitti (INAF OAPD), Alessandro Siviero (DFA UNIPD), Valerio Nobile (Liceo Scientifico Vida, Cremona), Andrea Farina (INAF OAPD)
on 30 Aug 2026; 15:22 UT
Credential Certification: Andrea Reguitti (andreareguitti@gmail.com)

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The Nova appeared in Sagitta on August 25.12 UT has been already presented in ATel#18008, ATel#18009, ATel#18012, and ATel#18014. We observed the Nova at the 122 cm Galileo telescope of Asiago during the third Summer Asiago School for Young Astronomers with Galileo Observations (ASYAGO) of 24-29 August 2026. We obtained four spectra of the Nova with the Boller & Chivens spectrograph with 300 lines/mm and 2.3 Angstrom/pixel covering 3300-7800 Angstrom, on the 25.86, 25.91, 26.87 and 29.82 UT August. In particular the spectra of 25.86-25.91 August have been obtained during the maximum luminosity of the Nova. We confirm the presence of P-Cygni profiles both in H-alpha and H-beta lines on 25 August, and its disappearance on 26 and 29 August, and the presence of the Fe II multiplet in all the spectra. We claim the evidence of the Balmer Jump in all our 25 August spectra, in the blue part of the spectrum, not visible in the spectra published in the aforementioned Telegrams. Using the guiding camera of the telescope we realized aperture photometry of the Nova at its luminosity peak obtaining in the visual band 6.99 (Aug 25.861 UT) 6.91 (Aug 25.887 UT) 6.96 (Aug 25.909 UT). On 29.93 UT August its luminosity dropped to mag. 9.2 visual leading us to consider the V0488 Sge as a fast nova (which would be 3 magnitudes drop in 10 days after the maximum) with 2.3 magnitudes drop in 4 days. Moreover the spectral evolution is rapid since in 4 days the spectrum changed from a photospheric blue continuum on August 25 to an orange continuum on August 26 to a nebular phase on August 29. Accompanying material: The spectra of 25, 26, 29 August 2026 of the Nova Sge 2026 with H lines identifications.

The spectra of 25, 26, 29 August 2026 of the Nova Sge 2026 with H lines identifications