Near‐Infrared Spectrophotometry and the CO Emission in V2274 Cygni (Nova Cygni 2001 No. 1)

Abstract

Infrared spectroscopy of V2274 Cygni (=Nova Cygni 2001 No. 1) is presented for two widely separated epochs, 17 and 370 days after discovery. In addition to the Paschen and Brackett series of H i, the early-time spectrum shows strong emission lines of C i and N i, fluorescently excited lines of O i, and emission from the first overtone of carbon monoxide. Because the initial data were probably acquired no more than 18 days after outburst, CO molecule formation occurred remarkably quickly in the dense, cool, carbon and oxygen rich ejecta. Rapid formation was also seen in NQ Vul, V842 Cen, and V705 Cas, three other novae in which first-overtone CO emission has been detected. Formation of the CO molecule may occur chemically in a process that requires H 2 as a precursor or directly through radiative association. The overtone emission of V2274 Cyg indicates a temperature of $2500 K. The vibrational levels show no obvious departures from thermal equilibrium, which may indicate high optical depths in the fundamental. A large 13 C/ 12 C ratio (0:83 AE 0:3) is also indicated by the observations, consistent with the fast CNO burning expected in novae explosions. By the time of the second epoch observations, the emission lines of the neutral C, N, and O had disappeared. He i 10830 was the dominant emission feature in the spectrum. In addition to the hydrogen lines, recombination features of He ii were also strong. The common nebular lines of [S iii] were seen but only two coronal line, [S viii] 9911 and [Si vi] 19645, were detected. The CO emission had disappeared, but a strong thermal dust component was present. The interstellar reddening for the system was found to be E(BÀV Þ ¼ 1:3. This extinction, together with the absolute magnitude derived from the rate of decline of the light curve, suggest a distance of $10.8 kpc. This places V2274 Cyg well out of the Galactic plane. The small number of novae with spectroscopic detections of carbon monoxide all have prominent C i lines, moderate speed classes and ejection velocities, exhibit marked dust formation events, and result from an explosion on a CO-type white dwarf. Based on these similarities, the spectrum of V2274 is proposed as a likely near-infrared spectral template for other novae that display carbon monoxide emission.

The hybrid, coronal lines nova V5588 Sgr (2011 N.2) and its six repeating secondary maxima

“…Most prominent among these CI lines are the 1.165, 1.175 µm region features in the J band and the strong cluster of lines beyond Br10 in the H band in the 1.74 to 1.80 µm region. Examples of these CI lines can be seen in the spectra of several FeII type novae viz., V1280 Sco and V2615 Oph (Das et al 2008;), V2274 Cyg (Rudy et al 2003), V1419 Aql (Lynch et al 1995) and V5579 Sgr (Raj, Ashok & Banerjee 2011). Earlier near-IR spectra, obtained around primary maximum, would have been highly valuable to check if the FeII type characterizing optical wavelengths at that time was similarly dominating the near-IR.…”

NOVA V2362 CYGNI (NOVA CYGNI 2006):SPITZER,SWIFT, AND GROUND-BASED SPECTRAL EVOLUTION

“…Similar spectra in the 0.5-2.5 μm region were obtained with the Visibleto-Near-Infrared Imaging Spectrograph (VNIRIS) on the Lick Observatory 120 telescope using a 2 arcsec slit and nodding by 20 arcsec along the slit to subtract out the background sky. Reduction techniques were standard and have been described in earlier papers, e.g., Rudy et al (2003). The Swift X-Ray Telescope observations were performed in photon counting mode.…”

L and M Band Infrared Studies of V4332 Sagittarii: Detection of the Water Ice Absorption Band at 3.05 μm and the CO Fundamental Band in Emission

“…There appear n p 1-0 to be only a few other detections of the CO fundamental in emission-mostly toward young stellar objects (YSOs) and Herbig AeBe stars (e.g., Blake & Boogert 2004;Pontoppidan et al 2002). In a few novae, emission in the CO first overtone bands has been seen (Rudy et al 2003, Table 3; Evans et al 1996), but the detection of the fundamental band appears rare (Lynch et al 1997). The expanded CO rovibrational spectrum in V4332 Sgr is shown in Figure 3.…”

“…This could possibly be the reason for the absence in V4332 Sgr of the first overtone CO bands at 2.3-2.45 mm, which need a higher temperature for excitation. These bands have been modeled to have a temperature in the range 2500-4500 K in novae (Rudy et al 2003;Evans et al 1996). Furthermore, the strong presence of AlO bands in V4332 Sgr in the same spectral region as the CO first overtone bands makes it difficult to draw definite conclusions on the absence/presence of the latter.…”