V1405 Cas (= PNV J23244760+6111140) now displaying Fe II emission

ATel #14577; S. N. Shore (Univ. of Pisa), C. Buil, P. Dubovsky, P. Berardi, M. Bajer, C. Boussin, J. Guarrò, F. Teyssier, E. Bertrand, J. M. Viannet, D. Boyd, F. Boubault, H. Allen, M. Le Lain, P. le Dû, P. Cazzato, J. Coffin, K. Shank, E. Bressinck, O. Garde, K. Gurney, R. Leadbeater (ARAS Group)
on 26 Apr 2021; 12:56 UT
Distributed as an Instant Email Notice Novae
Credential Certification: S. N. Shore (shore@df.unipi.it)

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We report that the slow nova Cas 2021 (V1405 Cas = PNV J23244760+6111140), discovered in outburst on 2021 Mar 18.4 (CBET #4945, ATel #14471, #14472, #14476, #14478, #14482, #14530) has begun to display Fe II absorption features. The nova has been continually monitored by ARAS observers with a variety of telescopes (ranging from 20 to 28 cm and with spectrographs ranging in resolution from about 518 to 9500 covering the optical interval from about 3400 - 7600 A since 2021 Mar. 19.7UT with an accumulated archive to date of over 90 spectra (all spectra and observational details are available from the ARAS archive website). The last spectrum to show no evidence for any Fe II absorption was obtained on 2021 Apr. 03.7UT; a very narrow emission at Fe II 5169 (FWZI ~ 100 km/s, vrad ~ 0 km/s) was present but the upper limit to any absorption at vrad> -2000 km/s was EW < 0.010 A) while on 2021 Apr. 6.7UT a strong, detached absorption was present (0.5 A) with a minimum at -1200 km/s (FWZI ~ 500 km/s), confirmed on Apr. 7.7UT). The absorption was both stronger (2.3 A) and broader (FWZI ~ 2000 km/s) on Apr 19.2UT; most strong optical of Fe II permitted showed similar profiles. In contrast, during the last observation, Si II 6347 showed very weak absorption and both Si II components continued to show the same narrow emission at vrad ~ 0 km/s as the Fe II lines. The P Cyg-like profiles on He I 4471, 5876, 6678, and 7065A showed the absorption component maximum radial absorption velocities of -1600 km/s contiguous with a broad emission component that extended to +1600 km/s (there was also enhanced emission at vrad ~ 0 km/s on these lines). Although absent on Apr. 14.8UT, Ca II K appeared in absorption on Apr.19.7 (vrad = -900 km/s, EW = 1.5A, no emission) and, aside from the Balmer, He I, Fe II, and Si II lines, the only other feature is a complex emission centered at around 6244 A (Fe II and Al II). The hydrogen series showed a systematic development. Although an absorption component on Halpha extending to -2500 km/s had been detected in the earlier spectra on Mar. 22UT, that had disappeared by Apr. 3 to be replaced by emission extending to the same velocity and a strong absorption core at about the same velocity as the He I and metal ion transitions, -1600 km/s; the blueward emission had vanished by Apr.22; the maximum emission velocity remains about -2000 km/s. The Balmer series in the last spectra, Apr. 19, showed a progression in the radial velocity of the absorption minimum from -1200 km/s at Halpha to -1000 km/s at Hdelta but with the same maximum velocities of -1600 km/s (absorption) and +2000 km/s (emission). Observations are continuing and will be available through the URL linked below.