Near Infrared spectroscopy of V1405 Cas (= Nova Cas 2021)

ATel #14665; C. E. Woodward (U. Minnesota) D. P.K. Banerjee (Physical Research Laboratory, India), A. Evans (Keele U.)
on 27 May 2021; 22:13 UT
Credential Certification: C.E. Woodward (chickw024@gmail.com)

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ATel #14622 reported that V1405 Cas entered a recombination phase associated with the optical rebrightening (ATel #14614) of this source near 2021 May 10.8. Here we report 0.7 to 4.2 micron spectra obtained on 2021 May 25.64 UT on the 3.2m IRTF telescope using SpeX in cross-dispersed mode with an 0.8 arcsec slit (R = 750) in photometric conditions and moderate seeing (1.1 arcsec at K-band). These observations follow almost immediately after the Fermi-LAT gamma-ray detection of the nova (ATel #14658). The NIR spectra show predominantly hydrogen recombination lines from the Paschen, Brackett (Br16-4 through Br5-4), Pfund (Pf22-5 through Pf18-5) and Humphreys (Hu22-6 through Hu14-6) series. Lines of He, N and O are also prominently seen while Carbon lines are very weak or absent. Also seen are the "1 micron Fe II lines," i.e., four individual Fe II features at 0.9997, 1.0501, 1.0863 and 1.1126 micron (see Rudy et al. 2000, ApJ 539, 166). The H and He lines are broad, with median FWHM velocities of the order 1250 km/s. Weak P-Cygni absorption features are present in the H lines (minima of -1300 km/s and widths of order 250 km/s). On the other hand all the HeI lines show pronounced P-Cygni features. No evidence for dust formation or first overtone Carbon monoxide emission is seen. No infrared coronal line emission is detected at this epoch. The integrated line fluxes (using a single gaussian profile fit) are of the order: Brackett-alpha 2.17E-10 erg/s/cm^2 and HeI (2.058 micron) 0.22e-10 erg/s/cm^2. Further infrared observations are encouraged, in part to support a forthcoming NASA Stratospheric Observatory for Infrared Astronomy (SOFIA) campaign.

These observations were conducted under the NASA IRTF program 2021A011. CEW acknowledges partial support provided by NASA through award SOF09-0029 issued by USRA to the U. Minnesota under NASA contract NNA17BF53C, and the Deutsches SOFIA Institut (DSI) under DLR contract 50 OK 0901 to the University of Stuttgart.