ARAS Group spectroscopic monitoring of the latest outburst of RS Oph
ATel #14868; S. N. Shore (Univ. of Pisa),H. Allen, M. Bajer, H. Barker, K. Bazan, P. Berardi, T. Bohlsen, C. Boussin, D. Boyd, E. Bryssinck, C. Buil, S. Charbonnel, S. Curry, J. B. Desrosiers, D. Doctor, P. A. Dubovsky, P. Dubreuil, C. Eldridge, L. Franco, O. Garde, J. Guarro, P. Le Dû, R. Leadbeater, V. Lecocq, J. Martin, F. Teyssier, O. Thizy, P. Velez (ARAS Group)
on 23 Aug 2021; 11:31 UT
Distributed as an Instant Email Notice Novae
Credential Certification: S. N. Shore (shore@df.unipi.it)
We report the results of continuing medium resolution (R > 9000) spectroscopic monitoring of RS Oph (see ATel#14866, #14834 and previous telegrams cited therein). Members of the ARAS group have been obtaining spectra with resolutions ranging from 500 to 30000. Higher resolution spectroscopic monitoring (R~9500-30000) began on Aug. 9.8. To date around 270 spectra have been archived, including those from quiescent monitoring from 2011-2021; the observation closest to outburst having been obtained on 2021 Jun. 7.9 (R ~ 940, 3950-7550A) that shows no major changes from the previous two years of monitoring apart from orbital modulation of the Balmer line profiles. Here we focus on the most recent developments.
A rich spectrum of permitted Fe-peak second spectrum lines were present from day 3 (taking 2021 Aug. 8.9 for the first epoch, the first photometric and gamma-ray observations to show the outburst, ATel#14834). Narrow Fe II 5169, for instance, was not present after Aug. 19.6 but the broad emission associated with post-shocked gas, [Vrad(max,blue) = -1500 km/s, (=Vrad,(max),red) = +2500 km/s) is both narrower and less symmetric than Hbeta and the higher Balmer lines (on Aug. 20, [-2000,2000]) while the cores of the Balmer line profiles still show wind absorption from the red giant, although it weakened steadily after Aug. 12. The narrow, wind emission is still present on the Fe II lines but the absorption component vanished from all metal lines around Aug. 13.5. One spectrum, with a resolution of 30000, obtained on Aug. 11 shows that although very weak, a vast number of Fe II, Ti II, and related transitions were present at levels varying from 0.1 to 2 relative to the continuum. A comparison with the 2010 Mar. 31 (Day 21) spectrum of V407 Cyg taken at R ~ 67000 with the NOT (Shore et al. 2011, A&A, 527, A98) shows that virtually all of the second spectrum permitted lines (Ti II, Cr II, Fe II, etc) have counterparts in the initial flashed spectrum (see Atel #14860) that are undetectable after approx. Aug. 17. Instead, a wind component, likely powered by the precursor, is growing on the permitted transitions, especially the Balmer and He I lines.
The He I profiles are now all composite, like the Balmer transitions, and with similar maximum radial velocities, about 1500 km/s (Aug. 21.8). The O I 7774 and 8446 lines have weakened and narrowed, the 8446 A profile also showing a similar structure to the He I and Balmer lines between [-200,200] km/s; the 7774 A triplet shows a similar narrower emission peak. and development. The narrow component is systematically strengthening relative to the broad, displaced component.
[N II] 5755 line has persisted as a narrow (FWZI ~ 130 km/s). It first appeared on Aug. 10 and showed increasing relative intensity through Aug. 21.9 with no evidence of a broad wing. A similarly narrow [Ar III] 7135A line first appeared on Aug. 17. and has been increasing. The [O III] 4363, 4959, 5007A lines, which first appeared on Aug. 17.8 (FWZI ~ 120 km/s) have been steadily increasing, the ratio of the N1/N2 lines is about 1/3, close to the nebular value and suggesting it is from the peripheral parts of the wind. The narrow forbidden lines are situated in the local minimum between the two peaks of He I and similarly for O I 8446, the same was observed during the V407 Cyg eruption due to photoionization.
The details of instruments and telescope apertures are provided on the ARAS website (below). Our observations are continuing as weather permits, all spectra are available in FITS files, with previews, through https://aras-database.github.io/database/rsoph.html .
ARAS Spectroscopic Database
