V1674 Her is a Neon Nova

ATel #14746; R. M. Wagner (Ohio State U.), C. E. Woodward (U. Minnesota), S. Starrfield (Arizona State U.), D. P. K. Banerjee (PRL, India), and A. Evans (Keele U., UK)
on 2 Jul 2021; 08:52 UT
Credential Certification: R. Mark Wagner (rmw@as.arizona.edu)

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We report spectroscopic observations of the classical nova V1674 Her (2021) obtained on 2021 June 30.418 UT with the Hiltner 2.4 m telescope (+OSMOS) of the MDM observatory on Kitt Peak, Arizona. Our spectrum covers the region 330 to 920 nm at a spectral resolution of 0.35 nm. The spectrum has changed significantly since our first spectroscopic observations obtained at several telescopes between 2021 June 13-16 UT (see ATEL #14723) in which it was clearly in the early Fe II (fireball) stage (ATel #14723). At the present time and 17 days into the outburst, our most recent spectra indicate that we are clearly in the nebular phase of the outburst. Earlier SpeX spectra with the IRTF also showed V1674 Her in the nebular stage in the near-infrared spectral region with the detection of several coronal lines (ATel #14741). We report here that broad [Ne V] 342.6 nm is now present in our flux-calibrated spectra and is the second strongest emission line in the optical region after Hα. We find that the [Ne III] pair at 386.9, 396.8 nm are present as well. [Ne IV] at 471.4, 472.4 nm may also be present but with the really broad lines it is heavily blended with He II 468.6 nm. In addition, there is a broad but weak line at 637.5 nm that could be attributable to [Fe X] but there is a lack of strong [Fe VII] 608.5 nm in the spectrum. [O III] 495.9, 500.7 nm emission lines are not obvious in our spectra as yet. The presence of these strong neon emission lines likely attributable to overabundances of neon demonstrate that V1674 Her is a member of the class of neon novae that include QU Vul (1984), V838 Her (1991), and V1974 Cyg (1992) among others. It is evolving more rapidly than V838 Her (1991) as described by Vanlandingham et al. (1996, MNRAS, 282, 563). With a t₂ of 1 day and a t₃ of 2.2 days, V1674 Her (2021) is the fastest nova on record. Continued spectroscopic observations to study the evolution of this exceptional nova are strongly encouraged.