Detection of Diatomic Molecules in the Dust Forming Nova V2676 Oph

Abstract

Novae are generally considered to be hot astronomical objects and show effective temperatures up to 10,000 K or higher at their visual maximum. But, it is theoretically predicted that the outer envelope of the nova outflow can become cool enough to form molecules that would be dissociated at high temperatures. We detected strong absorption bands of C 2 and CN radicals in the optical spectrum of Nova V2676 Oph, a very slow nova with dust formation. This is the first report of the detection of C 2 and the second one of CN in novae during outburst. Although such simple molecules are predicted to form in the envelope of the outflow based on previous studies, there are few reports of their detection. In the case of V2676 Oph, the presence of the molecular envelope is considered to be very transient, lasting several days only.

Optical and Near-infrared Study of Nova V2676 Oph 2012

“…The median radial velocity is 6 km s −1 , with an uncertainties of order 50 km s −1 , from convolving measurement errors with uncertainties in line rest wavelengths. Our observations are consistent with the results of Nagashima et al (2014Nagashima et al ( , 2015 and Kawakita et al (2015Kawakita et al ( , 2016. A list of the prominnet lines identified and the reddeningcorrected emission line fluxes (in erg s −1 cm −2 ) for selected epochs is given in Tables 3, 4 and 5.…”

“…The value for A V derived earlier is comparable with other estimated values for reddening e.g. A V = 2.39 ± 0.12 (Nagashima et al 2015) and A V = 2.67 ± 0.16 (Kawakita et al 2016) for R = 3.1 in the case of V2676 Oph. Alternatively, we can find the value of extinction from reddening E(B -V) ∼ 0.93 towards the nova direction taken from Schlafly & Finkbeiner (2011) which was estimated using the colors of stars with spectra in the Sloan Digital Sky Survey.…”

A Review of the Evolution of Classical Nova V2676 Oph: Formation of Molecules and Dust Grains

“…In addition to the MMRD relation, the visual extinction determined by the "Balmer decrement" method (which requires the assumptions about recombination of hydrogen atoms and physical conditions) may be not sufficiently accurate. Nagashima et al in 2015 [37] had obtained A V = 2.35 ± 0.11, from their spectroscopic observations, using the same method. Another determination based on a different method, by Kawakita et al in 2016 [33], found A V = 2.65 ± 0.15 by comparing the optical spectrum just after the visual-brightness maximum (which is dominated by absorption) with the synthesized spectrum of a supergiant.…”