I have re-computed the ephemeris for this eclipsing dwarf nova after applying the heliocentric correction to ATLAS data. The correct value of the initial epoch is HJD=2459513.8834. The period value has not changed (P=0.0819486 d).

Thanks to Sebastian Otero for pointing out that the epoch of mid-eclipse should be given in HJD (BJD) rather than in MJD.

Taking the opportunity, I would also like to report that the supercycle length for Rybka 2 is about 390 days.

Denis Denisenko

On Thu, Nov 4, 2021 at 10:55 PM Denis Denisenko d.v.denisenko@gmail.com wrote:

This dwarf nova in Lacerta was discovered by 9th-grade student Alexandra

Rybka in November 2020 while data mining from the URAT1 catalog (due to outburst at Epoch 2013.708). It was also in outburst on 1989-09-03 DSS red plate and on several PanSTARRS-1 images. AAVSO VSX entry: https://www.aavso.org/vsx/index.php?view=detail.top&oid=2214231

According to ATLAS data (Tonry et al., 2018) the latest superoutburst started on 2021 October 20th and peaked at 16.6o on Oct. 21st. Light curve from ATLAS forced photometry server in orange and cyan filters: http://scan.sai.msu.ru/~denis/Rybka2-ATLAS-LC.gif

During the outbursts this variable is showing the eclipses as deep as 2 magnitudes. See, for example, the light curve of October 2019 outburst from ZTF data (Masci et al., 2018): http://scan.sai.msu.ru/~denis/Rybka2-ZTF-Oct2019.gif

Using the combined ATLAS and ZTF data from four outbursts, I have found the best value of period to be P=0.0819486 d (118.006 minutes) and the epoch of mid-eclipse MJD=59513.379. After the linear detrending of outbursts (some for 0.15 mag/day, one for 0.12, the other for 0.10 mag/day) the following phased light curve was obtained: http://scan.sai.msu.ru/~denis/Rybka2-phased_LC.gif

Denis Denisenko