TY - JOUR
T1 - Infrared spectroscopy of the 2022 eruption of the recurrent nova U Sco
AU - Evans, A.
AU - Banerjee, D. P.K.
AU - Woodward, C. E.
AU - Geballe, T. R.
AU - Gehrz, R. D.
AU - Page, K. L.
AU - Starrfield, S.
N1 - Publisher Copyright:
© 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.
PY - 2023/7/1
Y1 - 2023/7/1
N2 - We present near-infrared spectroscopy of the 2022 eruption of the recurrent nova U Sco, over the period from 5.4 to 45.6 d after outburst. This is the most intensive infrared study of this nova. Our observations started early after the outburst and extended almost to the end of the 'Super Soft' X-ray phase. A major find is the presence of coronal lines from day 9.41, one of the earliest appearances of these in any nova, classical, or recurrent. The temperature of the coronal gas is 7 × 105 K. There is also evidence for the presence of much cooler (≲2.5 × 104 K) gas. Remarkable changes are seen in the He I 1.083 μ m line, the strength of which declines, then recovers, in anticorrelation with the X-ray behaviour. We conclude that shock ionization is the dominant excitation mechanism for the coronal line emission. There is evidence in the infrared spectra for the presence of black body emission at ∼20 000 K, which we tentatively identify with the irradiated secondary, and for free-free/free-bound emission. For the previously determined binary inclination of 82.7◦, the implied ejection velocities are as high as 22 000 km s−1. These velocities appear unprecedented in nova outflows, and are comparable to those seen in supernovae, thereby marking U Sco as a truly remarkable object.
AB - We present near-infrared spectroscopy of the 2022 eruption of the recurrent nova U Sco, over the period from 5.4 to 45.6 d after outburst. This is the most intensive infrared study of this nova. Our observations started early after the outburst and extended almost to the end of the 'Super Soft' X-ray phase. A major find is the presence of coronal lines from day 9.41, one of the earliest appearances of these in any nova, classical, or recurrent. The temperature of the coronal gas is 7 × 105 K. There is also evidence for the presence of much cooler (≲2.5 × 104 K) gas. Remarkable changes are seen in the He I 1.083 μ m line, the strength of which declines, then recovers, in anticorrelation with the X-ray behaviour. We conclude that shock ionization is the dominant excitation mechanism for the coronal line emission. There is evidence in the infrared spectra for the presence of black body emission at ∼20 000 K, which we tentatively identify with the irradiated secondary, and for free-free/free-bound emission. For the previously determined binary inclination of 82.7◦, the implied ejection velocities are as high as 22 000 km s−1. These velocities appear unprecedented in nova outflows, and are comparable to those seen in supernovae, thereby marking U Sco as a truly remarkable object.
KW - cataclysmic variables
KW - infrared: stars
KW - novae
KW - stars: individual: U Sco
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U2 - 10.1093/mnras/stad1209
DO - 10.1093/mnras/stad1209
M3 - Article
AN - SCOPUS:85161491548
SN - 0035-8711
VL - 522
SP - 4841
EP - 4851
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 4
ER -