Rapid disappearance of Carbon Monoxide emission in Nova 2020Sgr #2
ATel #13888; D. P. K. Banerjee (PRL, India), C. E. Woodward (University of Minnesota), A. Evans (Keele University), S. J. Bus (IfA, Hawaii), S. Starrfield (Arizona State University), R. M. Wagner (The Ohio State University)
on 23 Jul 2020; 04:10 UT
Credential Certification: Dipankar P.K. Banerjee (dpkb12345@gmail.com)
Subjects: Infra-Red, Nova
In ATel #13852, we had reported the detection of prominent Carbon Monoxide first overtone emission, observed on 30 June 2020 in the galactic nova NSgr2020#2 (equivalently ASASSN-20ga/ PGIR20dsv/ ZTF20abdpwst/ AT 2020lrv; ATel #13790). A new spectrum in the 0.7-2.5 micron region has been obtained on 2020 July 16 (under unfavourable sky conditions) with the infrared spectrograph SpeX (Rayner et al. 2003, PASP 115, 362) using a 0.5 arcsec x 15 arcsec slit in the SXD (short-cross dispersed) mode (R = 1200) on the NASA IRTF 3.2-m telescope.
The remarkable development noticed is that the CO emission has now disappeared, within a short span of approximately 15 days from the last observation. Whenever detected in a nova, first-overtone CO emission is seen to occur early after a nova's outburst and then get rapidly destroyed within a timescale of a week or a little more (e.g V2615 Oph, Nova Oph 2017, V496 Sct, V705 Cas; see Joshi, Banerjee & Srivastava, 2017, ApJ, 851, L30 for a compilation of CO detections in novae). The fleeting existence of CO in nova winds is perhaps one of the most challenging problems to explain. Since CO emission is generally seen to precede dust formation, monitoring of the optical light curve is encouraged. The AAVSO LC (in the unfiltered w/V zero pt. data) has been behaving in an interesting but unusual manner with the nova reaching a primary maximum of ~11.8 mag on 15 June 2020, then declining to ~ 13.8 mag around 25 June before showing a slow re-brightening that still continues today when it has reached about 12.6 mag.