(cba:news) eclipsing novalike variable in the period gap

Joe Patterson jop at astro.columbia.edu
Wed Nov 11 10:07:53 EST 2020

Hi CBAers,

As usual, Denisenko has dug up a super-interesting star!  It's a tad 
faint (18.0), but within the ken of the larger scopes in our network. 
The short period, the possible second period, the deep and broad 
eclipse, the suggestion of "old nova" status - these features all bring 
the star right into our wheelhouse!  And Lacerta still has plenty of 
life remaining in the autumn sky.

Definitely a target for a clear (or "luminance", assuming I know the 
meaning of that word) filter.  Colors not important.  Integration time, 
that's sort of debatable.  We seek good time resolution and good S/N - 
and of course they compete directly.  Very roughly, I'd say 90 s 
integrations are adequately fast. But we still don't know much about its 
periods, so that's just a number which popped into my head.  Most stars 
(there are only a few) with similar waveforms are OK with significantly 
longer integration times.


-------- Forwarded Message --------
Subject: [vsnet-alert 24923] ZTF J220423.33+501621.1 - eclipsing 
novalike variable in the period gap
Date: Tue, 10 Nov 2020 23:45:00 +0300
From: Denis Denisenko d.v.denisenko at gmail.com via vsnet-alert 
<vsnet-alert at ooruri.kusastro.kyoto-u.ac.jp>
Reply-To: Denis Denisenko <d.v.denisenko at gmail.com>
To: vsnet-alert at ooruri.kusastro.kyoto-u.ac.jp

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:


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

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