SALT high resolution spectroscopy of RS Oph: evidence for acceleration of the nova ejecta

ATel #14852; Joanna Mikolajewska (NCAC PAS), Elias Aydi (MSU), David Buckley (SAAO), Cezary Galan (NCAC PAS), Marina Orio (UoW/INAF)
on 12 Aug 2021; 01:47 UT
Credential Certification: Cezary Galan (cgalan@camk.edu.pl)

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We report on high-resolution optical spectroscopy of the symbiotic recurrent nova RS Oph (see ATels #14834, #14838, #14840, #14844, #14845, #14846, #14848) taken with the Southern African Large Telescope (SALT).

The observations were acquired on 2021-08-10.87 UTC, about 2 days after the outburst, with the nova at V ~ 5.2 mag. We used the High-Resolution Spectrograph (HRS; Crause et al. 2014, Proc. SPIE, 91476). The 30 s, 300 s, and 600 s spectra were taken in the HR mode of HRS with resolving power R~65000 - 740000 and wavelength coverage of 3800-8800 Å. The data were reduced with the SALT HRS MIDAS pipeline ( Kniazev et al. 2016, MNRAS 459, 3068).
The spectrum is dominated by broad P Cygni profiles of Balmer H I, Fe II, O I, and Mg II, along with weaker, broad lines of He I and [O I]. The presence of strong Fe II lines is particularly interesting. The Fe II (42) lines are the main contributors to the emission features at 4924 and 5018, respectively, and the Fe II (42) at 5169 is as strong. On the top of nova H I, He I, and Fe II lines, the narrow emission with central reversal, typical for symbiotic stars is also present. The expansion velocity of the ejecta estimated from the Hα and Hβ P Cyg profiles is ~-4200 km/s and ~-4700 km/s from the absorption center and the blue absorption edge, respectively, which compared with the velocities of ~ -3700 and -2700 km/s reported by Munari (ATel #14840) indicates that the ejecta are accelerating.

The NaI D and CaII H & K lines reveal complex profiles. In particular, in addition to strong interstellar lines, there are remarkable components at ~-48, ~-63, and ~-77 km/s, respectively, blueshifted with respect to the systemic velocity (γ=-38.7 km/s), practically identical with those reported by Patat et al. (2011, A&A 530, A63) and associated with circumstellar material.

SALT observations will be continued.

Based on observations collected under the SALT transient followup program 2018-2-LSP-001. Polish participation in SALT is funded by grant MNiSW DIR/WK/2016/07. JM and CG also acknowledge support from NCN 2017/27/B/ST9/01940.

Tentative emission line identifications:
H I (Balmer): 3970, 4102, 4340, 4861 and 6563 Å
He I: 4471, 4924, 5016, 5876, 6678, and 7065 Å
O I: 7477, 7773, and 8446 Å
[O I]: 6364 Å
Mg II: 8232 Å

Fe II lines:
Multiplet (27): 4233, 4385, and 4417 Å
Multiplet (28): 4179 and possibly 4297 Å
Multiplet (37): 4491, 4515, 4556, and 4629 Å
Multiplet (38): 4508, 4523, 4549, and 4584 Å
Multiplet (42): 4924, 5018 and 5169 Å
Multiplet (49): 5198, 5235, 5276, and 5317 Å
Multiplet (74): 6248, 6417, and 6456 Å