From jop at astro.columbia.edu  Wed Nov 11 10:07:53 2020
From: jop at astro.columbia.edu (Joe Patterson)
Date: Wed, 11 Nov 2020 10:07:53 -0500
Subject: (cba:news) eclipsing novalike variable in the period gap
In-Reply-To: <CA+ANhyeprufWFR2zvFk=3+dCztMNSE29qgYU+dxvbKUJu+x8uA@mail.gmail.com>
References: <CA+ANhyeprufWFR2zvFk=3+dCztMNSE29qgYU+dxvbKUJu+x8uA@mail.gmail.com>
Message-ID: <7bf9fd5e-95b3-5741-b4c3-24d97acef5c0@astro.columbia.edu>

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.

joe




-------- 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:

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

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From jop at astro.columbia.edu  Sat Nov 14 03:47:49 2020
From: jop at astro.columbia.edu (Joe Patterson)
Date: Sat, 14 Nov 2020 03:47:49 -0500
Subject: (cba:news) V392 Persei
Message-ID: <1f71f369-b3e7-77ca-e789-cc7e309604cd@astro.columbia.edu>

Sorry, this is more of a "chat' item... but I wanted to reach as many 
V392 Per observers as I can.

1. We still have a very great need for European coverage, especially 
early-night European coverage (and preferably all night, to join with 
North America).

2. As usual for unfiltered data (and really for all data), it's 
necessary to apply additive constants to put different observers on the 
same scale.  Those constants are determined by measurements which are 
SIMULTANEOUS.  There are two circumstances which make this particularly 
difficult.
(a) Changing comparison stars.  When the data are simultaneous and of 
good quality, a good measurement is made.  But when you change 
comparison stars (singular or plural), that additive offset could 
change.  I've noticed some variations as high as 0.15 mag.  That's fine 
- for the one night of observation.  But simultaneity is not achieved on 
most nights, so use of that additive constant could be erroneous.  And 
in searching for long periods (a few days or more), this can be a big 
systematic and unmeasurable error.

       This has always been true, but is usually not serious since I 
often subtract the mean magnitude anyway, which optimizes the search for 
short periods.  But V392 Per may have a several-day period, where it can 
be a problem.

(b) V392 Per has a close neighbor, and I imagine people have different 
strategies for dealing with it (include, exclude, report with or without 
subtraction, etc.).  Not a big deal as long as you always do the same 
thing.  (No particular recommendation, since it always depends on the 
precise details of telescope and quality of night.)

So... let me know if these issues could pose a problem with your data.
I measure the offsets in magnitude very frequently, so know that it's 
not a common problem.  But it can be - and for this star very reluctant 
to yield its secrets, I wanted to be extra vigilant.

joe p
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From jop at astro.columbia.edu  Sat Nov 21 18:53:39 2020
From: jop at astro.columbia.edu (Joe Patterson)
Date: Sat, 21 Nov 2020 18:53:39 -0500
Subject: (cba:news) V392 Per, finis!... and new Nov-Dec stars
Message-ID: <d4a2f0e8-f594-0ce0-d541-11f30fd38c02@astro.columbia.edu>

Hi CBAers,

Let's bring down the curtain on V392 Per.  Tremendous coverage, which I 
have greedily pounced on and worked out the periods.  The main signal is 
about 3.2 days, and there's a not-quite-coherent feature near 1.2 hours. 
  But neither signal is really in our happy zone, and the usual rule of 
thumb is: significant improvement requires doubling what you already 
have.  Too much.  So I'll write up what we have now, and let's move on.

Intermediate polars.  Some of you have adopted favorite and seasonally 
appropriate IPs.  Excellent strategy.  But here's a few of special 
importance which definitely need service: BG CMi, HT Cam, HZ Pup, V418 
Gem, V647 Aur, V667 Pup.  A 3-hr observation generally gives a good 
pulse timing.  And 10 distributed over an observing season enables a 
continuous cycle count.

Koji Mukai's listing of intermediate polars (the "NASA" listing) gives 
all the info you might need for these stars.  The common goal for all 
is: measure their long-term period change.  That's the "sociology" part. 
  However, many stars have their own quirks - sidebands, orbital 
signals, etc. - which distinguish them.  That's the "psychology" aspect. 
  Pretty much all IPs are a great hunting ground for CBA-style observation.

V597 Pup is of special interest - apparently an IP, an eclipser, and a 
nova.  Probably too faint... but take a look; if you can do it, it could 
be a mighty interesting target.

Finally, we have very long-term campaigns going for ES Cet and T Pyx. 
Both still in our nighttime sky.  It would great to get some data for 
the 2020-1 season.

joe




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From jop at astro.columbia.edu  Sun Nov 22 17:32:36 2020
From: jop at astro.columbia.edu (Joe Patterson)
Date: Sun, 22 Nov 2020 17:32:36 -0500
Subject: (cba:news) AH Mensae contaminating star
Message-ID: <32ff35ad-b2fa-e78d-b617-657913abcaa1@astro.columbia.edu>


Hi CBAers,

A few months ago Gordon notified me that this star - of high interest 
this year - has an unwanted companion of roughly equal brightness just 2 
arcsec away.  I forgot about this, but stumbled on the note as I was 
studying this year's data (from Gordon, Josch, and Berto).  At -81 
degrees dec, this doesn't concern many of you - but if you observe this 
star, be sure to use enough aperture to cleanly include both stars.  At 
13th magnitude, you can be generous.

And there's good reason to observe it.  It's one of the best and 
brightest "permanent superhump" systems in the sky.  I wrote one 
detailed paper on it in 1995, and we have a lot of archival data since. 
  I'm deeply burrowed in it now, and recommend this guy very strongly. 
It would be great to actually get 24-hour coverage.  The short summer 
nights (and those sadly wide oceans) probably prevent this - but we can 
get close.  Peter Nelson and Greg Bolt, are you reading?

joe
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From jop at astro.columbia.edu  Mon Nov 23 06:05:40 2020
From: jop at astro.columbia.edu (Joe Patterson)
Date: Mon, 23 Nov 2020 06:05:40 -0500
Subject: (cba:news) More on AH Men = Tafelberg
Message-ID: <0844d66d-296c-dad8-548f-f291b809852c@astro.columbia.edu>

Hi (mostly southern) CBAers,

Working through the 2020 data on AH Men, I note one feature that really 
helps in the period searches.  The star has somewhere between 3 and 5 
identifiable periodic signals, but there's hardly any of the 
night-to-night nonperiodic variability ("noise" to us) which hampers the 
study of virtually all CVs.   The mean nightly brightness hardly changes 
at all.  This means that you can breezily append nights together for a 
many-night period search, without some intermediate mathematical 
adjustment (e.g. subtract the mean) which can possibly hide a true 
signal or reveal a bogus signal.  Nice!

And, in particular, it means that you can merge data sets from the three 
major land masses in Earth's nether regions: South Africa, South 
America, Australia.  And we have ace observers in all three!

But since we do differential photometry, it's important that we not 
change comparison stars during a year's campaign.

Except for the last, these are not recommended practices in general. 
Cataclysmics will eat you alive if you assume that magnitude 15.73 on a 
Monday means the same thing as 15.73 on a Tuesday.  Night-to-night 
erratic variability is usually much stronger than the small periodic 
(and therefore interpretable) signals we like to study.

David Buckley reminded me that we once called this star "Tafelberg", and 
i used that alluring name in talks I gave about it, and in my 1995 
paper.  I'm not sure quite why, but i certainly like the practice of 
stellar nicknames.  I know Algol, the Demon Star... and 61 Cygni, the 
Flying Star.  Can you write and tell us of others you know?

joe
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