Detection of brightening and optical flickering of RS Ophiuchi

ATel #15339; Filipp Romanov (amateur astronomer, Russia)
on 19 Apr 2022; 23:49 UT
Credential Certification: Kirill Sokolovsky (kirx@scan.sai.msu.ru)

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Last year there was another eruption of the recurrent nova RS Oph. According to my visual brightness estimate with the unaided eye, it was 4.6 mag at 2021-08-09.63889, near the peak of its brightness.

I observed RS Oph remotely using 0.61-m f/6.5 corrected Dall-Kirkham robotic telescope (Lane, 2018, RTSRE, 1, 119) of Burke-Gaffney Observatory (Saint Mary's University in Halifax, Nova Scotia, Canada). Part of multicolour photometric data (dates are in UTC and correspond to the middle of the exposures) is presented below:

 
2022-02-01.41959 Ic = 9.70 +/- 0.01 
2022-03-05.38765 Ic = 9.54 +/- 0.01 
2022-03-14.31328 Ic = 9.63 +/- 0.01 
2022-03-30.25807 Ic = 9.56 +/- 0.01 
2022-03-31.30203 Ic = 9.57 +/- 0.03 
2022-04-03.29660 Ic = 9.59 +/- 0.02 
2022-04-06.28987 Ic = 9.61 +/- 0.01 
2022-04-07.28213 Ic = 9.51 +/- 0.01 
2022-04-12.26826 Ic = 9.38 +/- 0.01 
2022-04-13.31548 Ic = 9.30 +/- 0.01 
2022-04-16.32657 Ic = 9.31 +/- 0.03 
 
2022-02-01.41881 Rc = 10.88 +/- 0.02 
2022-03-05.38685 Rc = 10.65 +/- 0.01 
2022-03-14.31248 Rc = 10.68 +/- 0.01 
2022-03-30.25727 Rc = 10.61 +/- 0.02 
2022-03-31.30123 Rc = 10.66 +/- 0.04 
2022-04-03.29580 Rc = 10.72 +/- 0.01 
2022-04-06.28907 Rc = 10.74 +/- 0.01 
2022-04-07.28133 Rc = 10.58 +/- 0.01 
2022-04-12.26747 Rc = 10.39 +/- 0.01 
2022-04-13.31468 Rc = 10.28 +/- 0.01 
2022-04-16.32576 Rc = 10.29 +/- 0.02 
 
2022-02-01.41702 V = 12.09 +/- 0.04 
2022-03-05.38507 V = 11.87 +/- 0.03 
2022-03-14.31071 V = 12.03 +/- 0.02 
2022-03-30.25550 V = 11.78 +/- 0.02 
2022-03-31.29944 V = 11.80 +/- 0.05 
2022-04-03.29402 V = 11.81 +/- 0.03 
2022-04-06.28729 V = 11.79 +/- 0.02 
2022-04-07.27955 V = 11.58 +/- 0.01 
2022-04-12.26568 V = 11.40 +/- 0.02 
2022-04-13.31289 V = 11.28 +/- 0.01 
2022-04-16.32398 V = 11.25 +/- 0.04 
 
2022-02-01.41799 B = 13.31 +/- 0.02 
2022-03-05.38603 B = 13.37 +/- 0.01 
2022-03-14.31165 B = 13.32 +/- 0.02 
2022-03-30.25646 B = 13.14 +/- 0.05 
2022-03-31.30040 B = 13.14 +/- 0.10 
2022-04-03.29498 B = 13.12 +/- 0.01 
2022-04-06.28825 B = 13.09 +/- 0.01 
2022-04-07.28051 B = 12.79 +/- 0.01 
2022-04-12.26664 B = 12.75 +/- 0.01 
2022-04-13.31385 B = 12.58 +/- 0.01 
2022-04-16.32495 B = 12.54 +/- 0.01 

According to these data, rapid brightening started after 2022-04-06, with the largest amplitude in the B band. After the prediction in ATel #15296 that the flickering should appear in the next 30 days, I regularly requested one-hour time series observations with 60 seconds exposure time using photometric Johnson B filter.

I did not detect the flickering (present on 14 April 2022 as reported in ATel #15330) during observations from 2022-03-30.25646 to 2022-03-30.29991 UTC, the mean magnitude was 13.14 B +/- 0.05 and magnitude errors were similar to those of comparison stars. A day later, due to cloudiness, errors increased during the time series, which made it possible to measure only the mean magnitude: 13.14 B +/- 0.1.

On April 2022, from 03.24608 to 03.29498 UTC, I detected apparent magnitude variations with a peak-to-peak amplitude of 0.13 mag in B band, significantly larger than magnitude errors of comparison stars, and this is the first detection of optical flickering of RS Ophiuchi in these data. According to the observations from April 06.23469 to 06.28825 UTC, the magnitude variation is less than 0.1 mag and slightly differs from the magnitude errors of comparison stars.

From April 07.23120 to 07.28051 UTC, magnitude has changed from 12.96 to 12.79 B +/- 0.01, and this is the second reliable detection of flickering. As a result, I conclude that the flickering appeared between March 30 and April 3, 2022.

All photometry data were uploaded to the AAVSO International Database under my observer code RFDA.

The light curves of RS Oph for 2022 March 30, April 3 and April 7