The narrowing lines of RS Oph, its recombining flashed-wind, and the persistent outer neutral regions from Echelle spectral monitoring
ATel #14860; U. Munari (INAF Padova) and P. Valisa (ANS Collaboration)
on 13 Aug 2021; 17:30 UT
Credential Certification: U. Munari (ulisse.munari@oapd.inaf.it)
We report about the spectroscopic evolution of RS Oph that we are monitoring
at multi epochs each night with the Varese 0.84 + Echelle and Asiago 1.22m +
B&C telescopes. The new 2021 eruption of this recurrent nova has triggered a
widespread interest and observations over the whole electromagnetic spectrum
(ATels #14834, #14838, #14840, #14844, #14845, #14846, #14848, #14849,
#14850, #14852, #14855, #14857, #14858).
The very narrow emission component superimposed to the broad emission
lines, probably originating in the slow wind of the red giant (RG) ionized
by the initial UV-flash, is quickly declining in absolute flux, with an
e-folding time of about 60 hours for Balmer and FeII lines. This
recombination time corresponds to an electronic density of 1.1e+07 cm-3.
The corresponding values for the 2010 outburst of V407 Cyg were about 100
hours and a density 6.6e+06 cm-3.
Contrary to the narrow components, the narrow absorptions (also
superimposed to the broad emission) remains rather stable. Their
heliocentric radial velocity is constant at -64 km/s. Compared with the
barycentric velocity of RS Oph (-40 km/s, Fekel et al. 2000, AJ 119, 1375),
these narrow absorption seems to originate in the outer and still neutral
regions of the RG wind, characterized by a terminal wind velocity of about 24
km/s (at least toward the observer).
The broad emission lines originating from the nova ejecta are
monotonically reducing their FWHM, supporting a continued deceleration of
the ejecta while they plough through the RG wind and the circumstellar medium.
The average FWHM of Hgamma and Hdelta is 3400, 3000, 2450, 2050 km/s
for Aug 9.75, 10.75, 11.75, and 12.75 UT respectively.
The P-Cyg absorptions have nearly vanished from most of the lines.
The latest Echelle spectra could be revealing the signature of a bipolar
flow. A trapezoidal pedestal is apparently emerging in Halpha, as the broad
component continues to shrink and the veiling from the flashed-wind is
disappearing: on Aug 12.75 UT the pedestal is characterized by a velocity
span of 4400 km/s at the top and 7500 km/s at the base. It seems visible in
Hbeta too, but the blending with nearby FeII and HeI lines makes harder to
distinguish it.
