Strong [FeVII] emission persists in optical spectra of nova V1405 Cas

ATel #16089; C. E. Woodward (U. Minnesota), R. M. Wagner (LBTO/Ohio State U.), I. IIyin (AIP Potsdam), S. Starrfield (Arizona State U.)
on 19 Jun 2023; 18:35 UT
Credential Certification: C.E. Woodward (chickw024@gmail.com)

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V1405 Cas (ATel#14471) is a very slow nova identified by Munari and Valisa (ATel#15796) as a neon nova from optical spectra that included detection of [Fe VII] 608.629 nm on day +618, after the onset of the infrared coronal line phase which was reported on day +514.8 (ATel#15540). Recently, Rudy et al. (ATel#15934) report that the nova is still in a coronal line phase observing a strengthening of the [Fe VII] line relative to lines of H I. Here we report recent optical spectra obtained on 2023 June 16.986 UT on the Large Binocular Telescope (LBT) using PEPSI (Strassmeier et al. 2015 AN 336, 324) with a 1.5 arcsecond diameter beam (R=130 000, velocity resolution of the order 2.3 km/s per resolution element) under photometric conditions and moderate seeing (0.9 arcsecond). The optical spectra on day +833.22 show the clear presence of broad and structured emission line profiles from He II 468.571 nm, [Fe VI] 517.499 nm, [Fe VII] 608.629 nm, H I 656.280 nm, and He I 823.46 nm. No emission from H I 434.046 nm, [Ne IV] 472.415 nm, [Ar X] 553.60 nm, or [Fe X] 637.40 nm was detected above the continuum S/N (of > 100). No data were obtained using a cross disperser covering wavelengths near H I 486.363 nm (480.0 to 544.1 nm). The H I 656.280 nm line has a FWZI of approximately 2,700 km/s, with multiple structures across the line profile with strong components offset at -975 km/s, -820 km/s, -655 km/s, -437 km/s, -135 km/s, +100 km/s, +220 km/s, +310 km/s, and +800 km/s. The FWZI [Fe VII] 608.299 nm is approximately 2,450 km/s and its emission profile exhibits similar components as H I 656.280 nm. No P-Cygni profiles are evident. The observed integrated relative intensity ratios are (He II 468.571 / H I 656.280) = 0.548; ([Fe VI] 571.499 / H I 656.280) = 0.581; and ([Fe VII] 608.629 / H I 656.280) = 0.670. The strong [Fe VII] 608.629 nm line indicates that the density remains high in the emitting regions. Further optical and infrared observations are encouraged. The LBT is an international collaboration among institutions in the United States, Italy and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University, The Ohio State University, The University of Notre Dame, University of Minnesota and University of Virginia.