"Reverse hybrid" behavior of Nova Per 2020 = TCP J04291888+4354233
ATel #14230; Sandipan Borthakur, Vipin Kumar, Vishal Joshi, Mudit Srivastava, Dipankar P K Banerjee (Physical Research Laboratory, Ahmedabad, India)
on 28 Nov 2020; 05:28 UT
Credential Certification: Vishal Joshi (vjoshi@prl.res.in)
We confirm the findings of Munari et al. (ATel #14229) about a rapid evolution in the spectra of Nova Per 2020 as it rises towards maximum. TCP J04291888+4354233 was discovered by Seiji Ueda on UT 2020 Nov 25.813. We obtained optical spectra of the nova on subsequent nights on UT 2020 Nov 26.88 and on UT 2020 Nov 27.68 using the Mt. Abu Faint Object Spectrograph and Camera - Pathfinder (MFOSC-P) instrument on the PRL 1.2m Telescope at Mt. Abu, India. The spectra were recorded in two modes: Low-resolution mode with R ~ 500-600 covering the 4400-9000A region and a R ~ 2000 mode covering 6100-7100A centered around H-alpha.
Consistent with Munari et al. (ATel #14229), we also find that that the first night's spectrum showed prominent presence of several HeI lines (5876, 6678, 7065 Ang) accompanied by strong P Cygni features, NII (multiplet 3), and CII 7235A. However, on the second night, these lines have disappeared or weakened very largely and are replaced by FeII lines (prominent being the lines of the 42, 48, and 49 multiplets) with pronounced P-Cyg absorption
features. The appearance in the latter spectrum is that of a conventional Fe II class of nova. The H-alpha profile, taken with R = 2000, shows a rather dramatic change with clearly separated red and blue peaks on the first night with the blue peak significantly stronger and peak separation of 850 km/s. On the second night the double-peaked structure is not seen anymore (in the spectrum at R = 2000). On both nights, H-alpha displays a prominent P Cygni profile and the emission component has FWHM of ~ 1500 to 1600 km/s on both nights.
Thus the object shows a transition from a nova with some He/N spectral characteristics to a nova of the Fe II class, which is in the opposite sense of the transition observed in hybrid or FeIIb novae proposed by Williams (1992, AJ, 104, 725) in his classification scheme. Hence we refer to this as a reverse hybrid behavior. Hybrid or FeIIb novae sequentially exhibit both classes of spectra making a fairly rapid transition in a matter of weeks from an initial FeII spectrum to a He/N spectrum before developing into the nebular stage (Williams 1992). The reverse hybrid behavior seen here is rather uncommon. In recent times it has been seen, for example, in the optical and NIR spectra of the recurrent nova T Pyx (A. Ederoclite, 2014, ASPC, 490, 163; Joshi, Banerjee et al. 2014, MNRAS, 443, 559) and in V5558 Sgr in the optical (Tanaka J., et al. 2011, PASJ, 63, 911). We strongly encourage further monitoring of this nova.
