Near Infrared Coronal Line Emission in nova V1674 Herculis

ATel #14741; C. E. Woodward (U. Minnesota), D. P.K. Banerjee (PRL, India), A. Evans (Keele U., UK), R. M. Wagner (Ohio State U.), S. Starrfield (Arizona State U.)
on 28 Jun 2021; 00:11 UT
Credential Certification: C.E. Woodward (chickw024@gmail.com)

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Observations of the very fast nova V1674 Her (ATel #14740, # 14737, #14736) obtained on 2021 June 24.423 UT on the 3.2-m NASA IRTF telescope using SpeX (Rayner et al. 2003, PASP 115, 362) in cross-dispersed mode (SXD and LXD) with an 0.5 arcsec slit (R = 1200) under photometric conditions and good seeing (0.7 arcsec in the K-band) show a marked evolution in the 0.7 to 4.2 micron spectrum. While the nova continues to show strong HeI lines along with the other infrared features described in ATel #14728 (observations on 2021 June 18.544 UT), a major new development is that near infrared coronal lines (see Greenhouse et al. 1990, ApJ 352, 307) have begun to appear. Unambiguously detected in the 2021 June 24.423 UT spectra are the [Si VI] 1.9650, [Si VII] 2.4833, and [Al VI] 3.66 micron lines. Other possible coronal features tentatively identified include a feature that could be [S IX] 1.2523 micron (or an alternative identification is HeI 1.2530 micron) and a feature at 2.34 micron that could be [Ca XIII] 2.3211 micron. At approximately 11.5 days past maximum light, these SpeX observations are probably the earliest reported detection of infrared coronal emission in a nova. Both V1500 Cyg and V838 Her, two of the fastest novae with t2 times of 2 and 1 day(s) respectively, were first detected to show coronal emission at 29 and 17 days respectively past maximum light (Chandrasekhar, Ashok and Ragland 1993, J. Astrophys. Astr. 14, 7; Benjamin and Dinerstein 1990, AJ 100, 1588). The continuum in the thermal, 3.0 to 4.2 micron region, is weak and does not show any signs of significant dust emission. The most prominent lines in this region are Pfund 8-5 3.7406 micron and Br-alpha 4.0523 micron, with integrated single Guassian-fit line fluxes of approximately 1.37e-12 ergs/s/cm2, FWHM velocity of 5660 km/s and 6.34e-12 ergs/s/cm2, FWHM velocity of 4690 km/s, respectively. Further synoptic optical and infrared observations are warranted and encouraged.

These observations were conducted in part under IRTF program 2021A012, and the authors thank the NASA IRTF staff for their assistance.