Continuing optical spectroscopic monitoring of V488 Sge (Nova Sge 2026) by the ARAS group
ATel #18053; F. Teyssier, D. Cejudo, V. Desnoux, K. Shank, J. Michelet, E. Giradin, T. Bohlsen, R. Leadbeater, C. Buil, F. Sims, J. Marco, R. Pomillo, V. Lecocq, E. Bertrand, L. Franco, G. Bertrand, H. Allen, J. Hinefeld, S. Morata, W. Fisher (ARAS), S. N. Shore (Univ. of Pisa, INAF-OATS)
on 17 Sep 2026; 14:29 UT
Distributed as an Instant Email Notice Novae
Credential Certification: S. N. Shore (shore@df.unipi.it)
We report continuing low (R ~ 900) grism through medium resolution (R=9000) optical (from around 3800 - 9000A) echelle spectroscopic observations of Nova Sge 2026 (ATel #18009). Spectra have been systematically obtained since 2026 Aug. 25. The first observation showed P Cyg profiles with maximum velocities of -2000 km/s on the metal lines (e.g. Fe II (RMT42), Si II 6347,6371). No He I lines were present at that time. The first appearance of neutral helium was on Sep. 7.8 UT with a HWZI ~ 2000 km/s and no associated absorption. By that stage, the Balmer and He I 7065 emission lines displayed an ensemble of peaks at around -980, -420, +170, +600, +1100 km/s. By Sep. 11.1 UT the He I lines had doubled in flux and displaying the same knots present on the Balmer lines and Fe II (42), for which the P Cyg absorption was no longer present but the emission wings matched those of all other transitions. No Si II was present from this point on. The N III 4640 feature was prominent at this stage and by Sep. 13.8 UT a weak He II 4686 emission, showing the same peaks, was detected on the wing of the feature. Most significantly, the spectrum displayed [N II] 5755 with the same structure indicating that the ejecta had entered the optically thin stage; [O I] 6300,6364 were present but not 5577 (a strong density indicator), and strong emission with the same profile was observed for O I 7772, and 8446. The Ca II IRT was not present. The most recent spectrum, Sep.15.8, shows further development of the He I/II and Balmer lines, continued strengthening of [N II], and also N I 8212 and C II 7235. There is a weak, broad emission feature with the same knot structures at around 5313A that is consistent with N III 5314 but the identification is uncertain. All lines retain the same ensemble of knots and the same emission FWZI. No ionization stage above He II is yet confirmed but the X-rays should soon display the presence of a supersoft source, the opacity and ionization of the ejecta are approaching transparancy. The profiles are consistent with a nonspherical ejection with maximum velocity of around 3000 km/s and an inclination of around 65+/5 deg to the line of sight. Observations are continuing.
ARAS Database N Sge 2026
