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Near-infrared observations of SN 2016adj: detection of first overtone carbon monoxide emission

ATel #8976; D. P.K. Banerjee (PRL, India); M. S.Connelley + A. T.Tokunaga (IfA, Univ. of. Hawaii), R. D.Gehrz (Univ. of Minnesota), T. R. Geballe (Gemini Observtory), A. Evans (Keele University), J. Spyromilio (ESO, Garching), V. Joshi + N. M. Ashok + Mudit Srivastava (PRL, India)
on 21 Apr 2016; 20:13 UT
Credential Certification: Dipankar P.K. Banerjee (orion@prl.res.in)

Subjects: Infra-Red, Supernovae

Near-Infrared studies of supernova SN 2016adj in Centaurus A have been ongoing from Mt Abu (ATel #8686) since its discovery on 2016 February 8.563UT (ATel #8651). Recent spectra taken on 2016 April 7, 9 and 10 from Mt Abu using the 1.2m telescope consistently showed a pronounced rise to the red starting from around 2.29 $\mu$m and coinciding with the position of the first overtone (2-0) bandhead of carbon monoxide. To confirm whether this was due to CO emission, a high quality spectrum was obtained using SpeX, in the cross-dispersed mode, on the NASA 3m IRTF telescope on 2016 April 14 covering the 0.78 to 2.5 $\mu$m region. This spectrum confirms that there is strikingly strong CO emission seen from this SN extending upto to 2.5 micron. Individual bandheads are not resolved implying an expansion velocity above 2500 km/s and the shape of the emission is consistent with an LTE temperature above 3000K. The present CO detection, first made on 7 April 2016, takes place 58.21d after discovery and possibly makes this the earliest CO detection in a SN. To the best of our knowledge, the earliest detection to date of first overtone CO emission in any SN was in SN 2007gr at +70d after B(max) (Hunter et al. 2009). Further observations are planned and formal results of our spectroscopy will be presented soon.