Follow-up Imaging & Spectroscopy of Nova Sagittae 2026 (V488 Sge)

ATel #18033; M. Mugrauer (AIU Jena), L. Maul (AIU Jena), and P. Rajkumari (University of Wroclaw)
on 7 Sep 2026; 12:42 UT
Credential Certification: Markus Mugrauer (markus@astro.uni-jena.de)

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We carried out follow-up imaging and spectroscopic observations of Nova Sagittae 2026 (ATel #18009) on 1 and 2 September 2026 at the University Observatory Jena. We measured the apparent brightness of the nova using the Cassegrain-Teleskop-Kamera-II (CTK-II), while simultaneously carrying out spectroscopic observations of the nova with the Échelle spectrograph FLECHAS, which was used in its 2x2 binning mode, providing a resolving power of R~7400. On both observation dates, in addition to calibration data, three spectra of the nova were obtained with FLECHAS, each with a detector integration time of 900 seconds. Several prominent emission features are present in the nova's spectra. The strongest emission lines found in the spectral range covered by FLECHAS are those of the Balmer series of hydrogen (Hα, Hβ, and Hγ), followed by the emission line of neutral oxygen (OI 7774). In addition several emission lines of singly ionized iron are detected, the strongest of which are Fe II (4924), Fe II (5018), and Fe II (5169). All of the detected emission lines are significantly Doppler-broadened. On 1 September 2026 at 22:13 UT, the Balmer lines had a full width at half maximum FWHM = 3000 ± 100 km/s, and on 2 September 2026 at 20:34 UT, they had FWHM = 2800 ± 100 km/s. This indicates the high expansion velocity (v ~ 1400 km/s) of the gas ejected during the nova explosion. During our spectroscopic observations, the apparent brightness of the nova, as measured with the CTK-II, was B = 10.07 ± 0.06 mag, V = 9.62 ± 0.05 mag, R = 8.26 ± 0.02 mag, and I = 7.76 ± 0.01 mag on 1 September 2026 and B = 10.34 ± 0.06 mag, V = 9.88 ± 0.05 mag, R = 8.53 ± 0.02 mag, and I = 7.93 ± 0.01 mag on 2 September 2026. Between the two observation epochs in early September 2026, on average the Nova's brightness decreased by 0.24 ± 0.04 mag in the used photometric bands.

Imaging and Spectroscopic Data