J/ApJ/907/70 Spectroscopic observation of Nova Cas 2020 with FKO (Fujii+, 2021) ================================================================================ Transient Formation of C2 and CN in the Near-maximum Phase of Nova Cas 2020(=V1391 Cas) Fujii M., Arai A., Kawakita H. =2021ApJ...907...70F ================================================================================ ADC_Keywords: Novae; Spectra, optical; Spectra, infrared Keywords: Classical novae ; Slow novae ; DQ Herculis stars Abstract: Nova Cas 2020 was a second example of a classical nova forming both C_2_ and CN molecules during its near-maximum phase. The formation C_2_ and CN is indicative of the carbon-rich (C/O>1) gas envelope of the nova. Our low-resolution spectroscopic observations in the optical from UT 2020 July 31 to August 19 revealed the appearance and the disappearance of the molecular absorption bands of C_2_ and CN in Nova Cas 2020. These molecules were present during ~3days only. Based on analysis of the C_2_ Swan band profiles, C_2_ (and probably CN also) formed at ~5000K in the nova envelope (see ~8000K for typical novae at their visual brightness maxima). Spectral evolution and the formation conditions of the molecules are similar to those of V2676 Oph, which is the first example of a C_2_/CN-forming nova. We predict that a late-phase grain formation episode similar to that seen in V2676 Oph will occur in Nova Cas 2020. Description: We conducted the low-resolution spectroscopic observations using the 0.4m telescope (f/10) with a low-resolution spectrograph FBSPEC-III (R=640 at a wavelength of H{alpha}, corresponding to a slit width of 5") at Fujii-Kurosaki Observatory (FKO). Objects: ------------------------------------------------------- RA (2000) DE Designation(s) ------------------------------------------------------- 00 11 42.97 +66 11 19.0 Nova Cas 2020 = V* V1391 Cas ------------------------------------------------------- File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file 20200731.dat 16 1620 Data observed on 2020 Jul 31 20200810.dat 16 1619 Data observed on 2020 Aug 10 20200812.dat 16 1619 Data observed on 2020 Aug 12 20200813.dat 16 1619 Data observed on 2020 Aug 13 20200814.dat 16 1619 Data observed on 2020 Aug 14 20200815.dat 16 1619 Data observed on 2020 Aug 15 20200816.dat 16 1619 Data observed on 2020 Aug 16 20200817.dat 16 1619 Data observed on 2020 Aug 17 20200818.dat 16 1619 Data observed on 2020 Aug 18 20200819.dat 16 1619 Data observed on 2020 Aug 19 -------------------------------------------------------------------------------- See also: J/ApJS/214/26 : Line lists for CN isotopes transitions (Sneden+, 2014) Byte-by-byte Description of file: 20200[78][13][0123456789].dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 4 I4 0.1nm Wave [4500/9000] Wavelength (Angstrom) 6- 16 E11.6 --- Flux [1e-15/1e-11] Normalized flux -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Prepared by Coralie Fix [CDS], 14-Jun-2022