Nova Tau 2026 (V1452 Tau) is likely undergoing dust formation

ATel #18120; U. Munari (INAF Padova), S. Dallaporta, P. Valisa, A. Maitan, and A. Vagnozzi (ANS Collaboration)
on 27 Oct 2026; 13:43 UT
Credential Certification: U. Munari (ulisse.munari@oapd.inaf.it)

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The transient TCP J05210763+2338194 was discovered by the NMW-TexasTech survey on 2026-08-06.4109 UT at an unfiltered magnitude of 11.2 (ATel #17947), and designated Nova Tau 2026 (= V1452 Tau) in CBET #5723 following the spectroscopic classification reported in ATel #17950. Further spectroscopic observations were presented in ATels #17960, #17970, and #17972. A Swift UVOT grism spectrum for day +39 was described in ATel #18073, where an emission feature around 3131 Ang was tentatively identified as the 7Be II doublet.

Since discovery, we have maintained tight monitoring of Nova Tau 2026, with preliminary reports presented in ATels #17950 and #17970. Daily BVRI photometry transformed to the Landolt (2009) system has been obtained primarily with ANS Collaboration telescope ID 0310, with additional data provided by telescopes ID 2202 and ID 1302. Absolutely flux-calibrated spectroscopy (both low-resolution and high-resolution Echelle) is routinely acquired with the Varese 0.84m telescope.

Initially, the nova displayed a prolonged plateau phase at maximum brightness (with a superimposed low-amplitude modulation), which lasted for the first ~70 days after discovery. The mean decline rates (mag/day) and the amplitude (mag) of the superimposed variability during the plateau phase were 0.029, 0.036, 0.026, 0.028 mag/day and 0.53, 0.52, 0.37, 0.34 mag for the B, V, R, and I bands, respectively. The Fe II spectrum evolved slowly during the plateau, varying in phase (especially in the P-Cyg absorption components) with the photometric modulation.

Nova Tau 2026 persisted on the plateau till around 2026 Oct 20.0 UT, after which it embraced a steep decline in brightness. Our last photometric measurements read:

UT date	B	V	R	I
2026 Oct 19.956	12.339	11.802	10.511	9.940
2026 Oct 22.963	13.461	12.848	11.872	11.231
2026 Oct 25.919	15.355	14.767	13.352	12.645
2026 Oct 26.981	16.408	15.700	14.022	13.363

The sudden drop of ~4 mag in less than a week is similar to that observed in recent plateau novae V606 Vul and V1391 Cas, suggesting that Nova Tau 2026 is currently forming dust.

Low-resolution spectra of Nova Tau 2026 were obtained on Oct 26.98 UT with both the Varese 0.84m and Stroncone 0.50m telescopes, each equipped with a Multi-Mode mk.III spectrograph. These spectra remain largely similar to those obtained immediately prior to the drop in brightness, confirming that the cause is dust condensation in the ejecta. The main observed changes are a steeper flux drop in the continuum than in the emission lines, along with a redistribution of the lines' relative intensities, with [O I] 5577, 6300, 6364 Å becoming the strongest features in the optical spectrum after the Balmer lines and O I 7772, 8446 Ang. In addition, line widths changed selectively depending on whether the flux deficit primarily affected the core or the wings. These spectral changes can be understood in terms of non-spherically symmetric ejecta, where dust formed above the photosphere and well within the outer radius of the expanding envelope.