RS Oph emerges from solar conjunction showing great changes
ATel #15169; U. Munari (INAF Padova), P. Valisa and S. Dallaporta (ANS Collaboration)
on 19 Jan 2022; 22:32 UT
Credential Certification: U. Munari (ulisse.munari@oapd.inaf.it)
Subjects: Optical, Cataclysmic Variable, Nova
After two months of non-observability, RS Oph has recently emerged from
the Solar conjunction. We have resumed collecting photometric and
spectroscopic data for the ongoing outburst (eg ATel #14834, #14840, #14844,
#14855, #14864, #14886) and found RS Oph to have greatly evolved compared to
mid-November when it plunged into the conjunction. RS Oph is still tracking
closely the photometric evolution of the previous outburst, as shown in
this
comparison of the lightcurve for the 2021 (ANS Collaboration data)
and 2006 outbursts (from Munari et al. 2007BaltA..16...46M). The most
recent BVRI observations that we have collected with ANS Collaboration ID
0310 telescope are listed in the table below (days counted from maximum
brightness on Aug 09.58 UT), where they are compared with our last
measurement before the conjunction and the median values over the 2008-2020
period between the outbursts.
| day | UT | B | B-V | V-R | V-I |
|---|
| +95.02 | Nov 12.704 | 12.046 | +0.661 | +1.418 | +1.887 |
| gap due to solar conjunction |
| +156.54 | Jan 13.221 | 13.235 | +1.555 | +1.110 | +2.154 |
| +157.54 | Jan 14.220 | 13.251 | +1.498 | +1.153 | +2.123 |
| +158.53 | Jan 15.218 | 13.240 | +1.489 | +1.184 | +2.156 |
| +159.53 | Jan 16.214 | 13.319 | +1.541 | +1.045 | +2.069 |
| median values in quiescence 2008-2020: |
| | 11.95 | +1.112 | +0.932 | +1.807 |
Immediately before the conjunction, RS Oph was still bluer than in
quiescence (note that the V-R color was dominated by an extremely strong
Halpha), but has turned fainter and redder upon emersion: the nova ejecta
that were still providing a substantial contribution to the overall brightness in
mid November, have now diluted into the surrounding space. There seems to
be less gas now than in quiescence for the still hot WD to ionize, as the
cavity emptied by the nova ejecta may have not yet been replenished by the
wind of the RG, and the accretion disk may still be reforming.
Echelle spectra of RS Oph have been obtained on 2022 Jan 16.22, 18.23 and
19.21 UT with the Varese 0.84m telescope which is maintaining a tight
monitoring since the onset of the outburst (Munari and Valisa 2021, arXiv
2109.01101). The spectrum for Jan 18 is compared
here with one from Nov 19, our last observation before the
conjunction. The ionization degree has reduced: the strong [FeXI] 7890 has
disappeared, [FeX] 6375 has declined to 1/12, while [FeVII] is remaining
constant. Other emission lines have reduced in intensity to about 1/3, with
the exception of the broad (FWHM=1300 km/s) [OIII] and [NII] lines from the
nova ejecta, that keep expanding at constant velocity after breaking free of
the RG wind. The triple structure of permitted and narrow emission lines is
still well visible in the Balmer lines, less so for the others as the bluer
of the three components is becoming lost in the background continuum from
the RG.
