Optical Spectroscopy Suggests the Fast Nova V1674 Her has Returned to Quiescence

ATel #15312; R. M. Wagner (Ohio State U.), C. E. Woodward (U. Minnesota), S. Starrfield (Arizona State U.), J. Rupert (MDM Observatory)
on 5 Apr 2022; 00:09 UT
Credential Certification: R. Mark Wagner (rmw@as.arizona.edu)

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The very fast nova V1674 Her (ATel #14704) has recently emerged from solar conjunction. We report optical spectroscopic observations (range: 397-686 nm; resolution 0.3 nm) obtained on 2022 March 27.45 UT with the 2.4 m Hiltner telescope (+OSMOS) of the MDM Observatory on Kitt Peak. The spectrum exhibits Balmer emission lines of Hα, Hβ and Hγ, He II 468.6 and 541.1 nm, He I 667.8 nm, and C III at 465.0 nm superposed on a blue continuum. Forbidden emission lines that were reported during the nova outburst (ATel #14746, #14723, 14720, #14710, #14704) are not present in our recent spectrum. He II 468.6 nm is the strongest line now present with a resolution-corrected FWHM of about 930 km/s and an observed integrated flux of about 5 × 10^-15 erg s^-1 cm^-2. For Hα and Hβ, we find corrected FWHM of 850 and 680 km/s respectively with the Hα line profile showing some structure and being asymmetric to the blue. These velocities are far less than the approximately 6000 km/s measured near the peak of the outburst and suggest that we are now looking at a separate component of the system from the ejected gases. The nova outburst is over and the recent spectrum is now similar to some nova-like cataclysmic variable stars which indicates that emission from the underlying binary system is now dominating the spectrum. Based on the 501 s oscillation detected before the outburst by Mroz et al. (ATEL #14720) and later by Patterson et al. (ATEL #14856) during the outburst, the current similarity of our spectrum showing strong He II emission and line widths to some cataclysmic variable stars strengthens the association of V1674 Her to the class of intermediate polars or DQ Her stars.