Carbon Monoxide Emission in Nova Cassiopeiae 2020 (TCP J00114297+6611190)

ATel #13967; Ray W. Russell (Observations Unlimited), Michael L. Sitko (Space Science Institute), Richard J. Rudy (Kookoosint Scientific), M. Fujii (Fujii-Kurosaki Observatory), A. Arai (Koyama Astronomical Observatory), H. Kawakita (Koyama Astronomical Observatory)
on 25 Aug 2020; 03:50 UT
Credential Certification: Richard Rudy (richard.j.rudy@aero.org)

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We report the results of infrared spectroscopic measurements of Nova Cassiopeiae 2020 (=TCP J00114297+6611190) obtained on the night of 2020 August 17.54 from the NASA Infrared Telescope Facility from Mauna Kea, Hawaii. The observations spanned the wavelength range 0.7-5.4 microns and were acquired with the SpeX facility instrument. Observations were acquired in both cross-dispersed mode, to obtain high resolution spectroscopy, and prism mode, to more precisely measure the brightness. The A0 V star HR 6829 was used as a calibrator. It closely matched the nova in airmass (typically less than 0.1). The outburst of Nova Cas 2020 was first detected 2020 July 27.231 (ATel #13904) and was classified as a classical nova by Sokolovsky et al. (ATel #13903). Fujii et al. (ATel #13941) reported the detection of molecular absorption bands of C₂ and CN on 2020 August 12.71 (UT), which prompted us to search for carbon monoxide in the infrared. We found strong emission from both the CO fundamental and first overtone. Near simultaneous (2020 August 17.53) low-resolution (R~500) optical spectroscopic observations with the Fujii-Kurosaki Observatory in Okayama Japan indicated that the optical C₂ and CN absorption features had disappeared by this time. These features were present on August 13 and observations from the intervening nights are being reviewed to narrow down the time of disappearance. Inspection of the CO first overtone indicates that a significant overabundance of ¹³C (relative to solar) is present with a ratio to ¹²C of about 0.6. The atomic emission lines are dominated by C I. While other low excitation features are also present (H I, N I, O I, Na I, Ca II, Fe II), the C I multiplet at 1.0691 microns is the strongest feature in our spectral range. Numerous other C I transitions are also present. At the time of these measurements, there was no indication of the presence of dust in the nova ejecta but dust formation will almost certainly take place sometime in the next several weeks. Normalizing the high resolution spectroscopy to the prism mode data, we obtained the following magnitudes for the nova: [J] = 8.23 , [H] = 7.56, and [K_short] = 7.10. An approximate I-band measurement of 9.9 was obtained in the same manner. We would like to thank John Rayner and Bobby Bus of the Infrared Telescope Facility for making the time available to acquire this target of opportunity on very short notice, and Greg Osterman for assisting us in obtaining the observations.