[FeX] and [FeXI] coronal lines now present in Nova Her 2021

ATel #14824; Ulisse Munari (INAF Padova)
on 1 Aug 2021; 15:38 UT
Credential Certification: U. Munari (ulisse.munari@oapd.inaf.it)

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Nova Her 2021 (= 1674 Her = TCP J18573095+1653396) has been discovered on 2021 June 12.537 UT by Seiji Ueda and spectroscopically classified as a nova by Munari et al. (ATel #14704). It has reached a very bright maximum (B=6.903, V=6.184, R=5.749, I=5.232 on June 12.862 UT according to ANS Collaboration monitoring) and this favored follow-up observations and detection at all wavelengths (ATel #14805, 14798, 14776, 14758, 14747, 14740, 14737, 14736, 14731, 14728, #14723, 14720, 14718, 14713, 14710, 14705, 14658, 14530).

Woodward et al. (ATel #14741) reported about initial appearance of infrared coronal emission lines in a spectrum of the nova they obtained with SpeX on June 24.4 UT, probably the detection at the earliest epoch (11.5 days) of any nova. Two weeks later, when Woodward et al. (ATel #14765) re-observed the nova again with SpeX on July 7.3 UT, the coronal lines became the dominant infrared spectral feature, second in intensity only to HeI 1.083 micron. Wagner et al. (ATel #14746) classified V1674 Her as a Neon Nova on a spectrum they obtained on June 30.4 UT, in which [NeV] 3427 was very bright and second in intensity only to Halpha. The presence of [FeX] 6375 was considered uncertain given the absence of [FeVII] 6087.

Coronal lines are now present also in optical spectra. The table below compares the integrated flux of representative emission lines (in erg/cm2/sec) on two spectra of Nova Her 2021 we have obtained with the Asiago 1.22m telescope. On July 10.91 Halpha was still stronger than [NeV] 3427, but this reversed by July 29.94. [FeXI] 7892 has clearly emerged in emission on the second epoch. Both the underlying continuum and all forbidden emission lines declined by the same 2.5 factor between the two spectra (cf. their EW in the table). Permitted lines have declined faster: 3.1 times for Balmer, and 4.0 times for HeI and HeII. The quickly retracing HeII 4686 is probably the main reason behind the decline in EW of the [NeIV]+HeII+NIII blend centered at 4690 Ang. All lines at both epochs remain very broad (FWHM=5500 km/s), with [NeV] and [NeIII] showing a mildly double-peaked profile and all other lines a rounded top.