Further Infrared Spectroscopy of RS Oph on day +34 reveals Coronal Line Emission

ATel #14910; C. E. Woodward (U. Minnesota), D. P.K. Banerjee (PRL, India), A. Evans (Keele U., UK), S. Starrfield (Arizona State U.), R. M. Wagner (Ohio State U.), R. D. Gehrz (U. Minnesota)
on 12 Sep 2021; 19:37 UT
Credential Certification: C.E. Woodward (chickw024@gmail.com)

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Low resolution (R = 1200) near-infrared (0.70 to 2.54 micron) spectroscopy of RS Oph (ATEL#14909, #14908, #14906, #14901, #14883, #14881 among others) obtained with SpeX (Rayner et al. 2003, PASP 115, 362) in short crossed-dispersed (SXD) mode on 2021 Sept 11.221 UT (approximately day +34 after eruption) on the NASA IRTF 3.2-m under good sky conditions (seeing 0.6 arcsec in the K-band) show that infrared coronal line emission (see Benjamin and Dinerstein 1990, AJ 100, 1588; Greenhouse et al. 1998, ApJ 352, 307) is now evident. In addition, the FWHM of the hydrogen emission lines are narrowing, and the red-wing asymmetries and saddle-shaped line profile peaks are disappearing (see ATEL#14866). The broad, blended emission complexes seen on day+12 (ATEL# 14866) now are resolving into individual line components, and multiple He II emission lines are now strong. Infrared coronal lines present, and representative observed fluxes (erg/s/cm2) include [S VIII] 0.9914 micron (2.8e-11), [S IX] 1.253 micron (3.4e-11), [Si X] 1.4305 micron (2.5e-11), [Si VI] 1.9650 micron, and [Si VII] 2.4833 micron (1.4e-11), with all wavelengths in vacuum. Also present is the line emission feature at 2.090 micron whose identification remains elusive. These latter detections substantiate reports of the detection of [Ne V] 0.3427 micron and coronal [FeX] 0.6375 micron lines by Munari et al. (ATEL#14895) just prior to the onset of the super-soft source (SSS) x-ray phase near 2021 September 04, as communicated by Page et al. (ATEL#14894) based on Neil Geherls SWIFT XRT observations. Currently, at the epoch of these latest SpeX observations discussed herein, the FWHM of the H emission lines (derived from the Br-series 19 to 9 lines in the H-band) exhibit an average velocity of 610 km/s. The observed fluxes (gaussian fit, erg/s/cm2) of Pa-β and Br-γ are 3.6e-10 and 6.5e-11, respectively while that of He I 10830 is 2.1e-9. Interestingly, the 12C16O band heads from 2.29 micron onwards, arising from the red giant secondary, are being detected very much earlier than in the 2006 outburst (they were not seen even on day 55; Evans et al. 2007, MNRAS 374, L1). We are examining whether the approximately 0.5 difference in the orbital phase of the red giant between the 2006 and 2021 eruptions (estimated using the ephemerides of Brandi et al. 2009, A&A 497, 815), could be responsible for the early appearance of the CO features in the current outburst. Clearly further infrared spectroscopic observations are encouraged.

The investigators are grateful to the NASA IRTF for providing the quick-access DDT opportunity (2021B996), and we thank the observatory staff for their assistance.