[vsnet-alert 24923] ZTF J220423.33+501621.1 - eclipsing novalike variable in the period gap

[Denis Denisenko d.v.denisenko@gmail.com via vsnet-alert]

Search for hidden CVs among the short-period eclipsing variables in
ZTF catalog (Chen et al., 2020) has brought a very interesting result.
The object in Lacerta ZTF J220423.33+501621.1 listed as EA with
P=0.200253 d, see
https://www.aavso.org/vsx/index.php?view=detail.top&oid=2132873 has
turned out to be a novalike variable with a twice shorter period
0.1001276 d (2.403 hr). Its true nature was revealed using the data
from IPHAS DR2 catalog (Barentsen et al., 2014) with the following
magnitudes: r=17.99(2), i=17.59(3), Ha=17.32(2).

The eclipse depth is more than 1 magnitude. There cannot be two
eclipses per period both deeper than 0.75m, thus the value from ZTF
Catalog of periodic variables is incorrect. The following phased light
curve with P=0.1001276 d was obtained from ZTF DR3 data (Masci et al.,
2019) at irsa.ipac.caltech.edu:

http://scan.sai.msu.ru/~denis/J220423+501621-phased_LC.gif

Note the asymmetry of the "shoulders" before and after the eclipse,
especially obvious in the red filter. There is also a hint of
short-period variations with a possible secondary period P2=0.0169529
d. Time-resolved photometry with the large scopes is encouraged.

There are several examples of classical Novae in the period gap (V
Per, V597 Pup, QU Vul) with some of those showing very similar orbital
light curves. ZTF J220423.33+501621.1 may be the past Nova. Given the
galactic latitude of -4.2, the DASCH data for that part of sky are not
yet publicly available.

Revision to VSX submitted.

Denis Denisenko