From jop at astro.columbia.edu  Mon Nov 13 06:10:18 2017
From: jop at astro.columbia.edu (Joe Patterson)
Date: Mon, 13 Nov 2017 06:10:18 -0500
Subject: (cba:news) V713 Cep outburst; also VZ Scl, IM Eri (no go)
In-Reply-To: <E1eE3NC-0005kZ-BX@ori.kusastro.kyoto-u.ac.jp>
References: <E1eE3NC-0005kZ-BX@ori.kusastro.kyoto-u.ac.jp>
Message-ID: <766a8811-d5e5-e853-4a65-2fdcf8e8e9a4@astro.columbia.edu>

V713 Cep richly deserves observation.  If in superoutburst, it's a GREAT 
target.  If in normal outburst, it's an excellent target.  And even if 
in quiescence, it's not too shabby either.

With our recent successes* re WZ Sge and ES Cet, I've come to realize 
that we are in a great position to make some impactful studies of 
orbital-period changes.  For years I didn't think so, because with our 
small scopes, our signal-to-noise is poor near the bottoms of typical 
deep eclipses (typically mag 17-20), or typical shallow eclipses (just 
0.2 mag deep).  Now I realize: WRONG on both counts.  Even with 
40-second integrations, it's easy for us to get an accuracy ~5 seconds - 
because integrative sampling is equivalent to instantaneous sampling, 
and because we commonly get very large amounts of data (say 40 eclipses 
per season).

Plus we're there year after year.  Some of the present campaigns are in 
part motivated by orbital-period issues (BT Mon**, X Cha, OY Car, U Gem).

Two stars to discontinue coverage: VZ Scl (excellent season, but we're 
done) and IM Eri (analysis of last year's data suggests this star is 
really complicated!).

joe

*Success here meaning completion of a paper reporting a many-year 
campaign and its consequences.  We have some smaller successes along the 
way, of course.

**BT Mon is special, because its Porb = 0.3338 days.  Thus its eclipses 
drift by only 2 minutes per day.  So space out your observations of this 
guy.  We want the full orbital light curve, not just the (very deep!) 
eclipse.  But it's NOT a star for the usual CBA style ("hit it every 
night, in as dense a cluster as weather permits").

joe

Beautiful planetary conjunction in tonight's morning sky!


-------- Forwarded Message --------
Subject: [vsnet-outburst 21482] V713 Cep outburst
Date: Mon, 13 Nov 2017 10:17:14 +0900
From: Taichi Kato <tkato at kusastro.kyoto-u.ac.jp>
To: suuma at yahoogroups.com, variable_star_forum at yahoogroups.com, 
vsnet-alert at ooruri.kusastro.kyoto-u.ac.jp, vsnet-alert at yahoogroups.com, 
vsnet-campaign-dn at ooruri.kusastro.kyoto-u.ac.jp, 
vsnet-outburst at ooruri.kusastro.kyoto-u.ac.jp, vsnet-outburst at yahoogroups.com

V713 Cep outburst

    Eclipsing dwarf nova below the period gap.  No superoutburst
has been observed.

   YYYYMMDD(UT)   mag  observer
   20171030.521  <163c  (Mitsutaka Hiraga)
   20171108.516  <163c  (Mitsutaka Hiraga)
   20171112.794  158C  (Jeremy Shears)


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From jop at astro.columbia.edu  Tue Nov 14 08:49:50 2017
From: jop at astro.columbia.edu (Joe Patterson)
Date: Tue, 14 Nov 2017 08:49:50 -0500
Subject: (cba:news) bt mon eclipses, and classical novae in general
Message-ID: <8fd879de-43e0-6b81-f804-9d03805d572d@astro.columbia.edu>

Enrique, David Cejudo, and Donn Starkey have obtained time series on BT 
Mon.  The eclipses are now occurring at the end of the "night" (meaning 
observable interval in darkness) in Europe, and at the beginning of the 
night in the USA.  Since the period slightly exceeds 0.33333333 d, the 
eclipses will creep later and later, and hence become good targets for 
observers at USA longitudes.  Not so good for Europe, generally.

HOWEVER... while eclipses are the prime motivator, we're interested in 
the whole orbital light curve. Based on this first look, it seems to 
have more bumps and features than past studies have shown.  So consider 
it a good target at other times.

And, on a grander scale...

The  orbital light curves of old novae are very poorly understood. 
Actually, probably not understood at all.  The published studies are 
star-by-star, one to a customer, and usually based on 1-2 high-speed 
light curves.  But erratic flickering is always present, so orbital 
features other than a deep eclipse are never clear from these studies. 
It's easy for us, since we cover many orbital cycles - maybe 50 or more 
(so flickering is smoothed over).

Also, these light curves ought to CHANGE as the cooling of the WD 
proceeds.  So one ought to study the light curves every few years.  It's 
not as simple as just "outburst" and "quiescence".

The *general* trend seems to be: not much variability within 3-4 mag of 
peak, then a small-but-growing amplitude signal emerges.  That's what T 
Pyx showed (see out recent paper), and some others (V1494 Aql, which 
we're studying thoroughly for these effects).  Select some seasonally- 
and magnitude-appropriate old novae, and see what you get.

My favorites this season are V Per and QZ Aur - both eclipsers, but both 
quite faint.  But plenty of other good ones out there (DN Gem and DM Gem 
are candidates; T Aur isn't - but only because we've just finished that 
study, thanks to Shawn, Tonny, and Jim Boardman).  Beautiful result!

joe
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From jop at astro.columbia.edu  Thu Nov 16 13:13:21 2017
From: jop at astro.columbia.edu (Joe Patterson)
Date: Thu, 16 Nov 2017 13:13:21 -0500
Subject: (cba:news) northern old novae
Message-ID: <0b3d1689-cde4-346a-6681-c97be6890248@astro.columbia.edu>

More on the "old nova" project...

Enrique has obtained a week of coverage on V Per.  At 18.5, it's a very 
challenging target.  Still, some USA observers could handle it, and that 
would provide the longitude span that enables us to do sensitive period 
search.  For the next 1-3 weeks, it's a very good target for the 
ambitious.  I can see now that the orbital period is stable, which was 
my #1 question, but the other questions - superhumps, orbital waves, and 
past periods - are still up in the air.

DN Gem and DM Gem are 16th magnitude old novae that are inadequately 
studied.  Red meat for us! - especially DN since its orbital period is 
"known" to be pretty short (3 hours).

And in the south, HZ Pup and T Pyx are good choices, having finally 
poked out from behind the Sun.

joe
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From jop at astro.columbia.edu  Sat Nov 18 09:13:17 2017
From: jop at astro.columbia.edu (Joe Patterson)
Date: Sat, 18 Nov 2017 09:13:17 -0500
Subject: (cba:news) FO Aquarii, keep the faith
Message-ID: <f3b4f36d-29c8-6ee9-4cd3-aa88d012619a@astro.columbia.edu>

Hi CBAers,

Some of you still have FO Aqr in your observing programs - for 
occasional coverage - despite the unfavorable sky location.  For our 
time-series photometry, an equatorial star 6 hours out of season is 
usually a no-fly zone!  But this year is different.  The usual dominant 
signals are still present, but the mean light has been fading throughout 
the season.  Now at 14.9, and seemingly still diving.  Over the years it 
has averaged about 13.7, so it's not exactly a call-911 deal.  Since it 
was comparably low early in the previous season (2016), I'd call it a 
"somewhat low but somewhat unstable" state.  Accurate, but not real catchy.

In a CV, is this *significant*?  Hard to say, since most of the previous 
35 years (mostly ours) used differential photometry, so the constancy of 
mean light over this interval is only good to around +-0.4 mag.  I would 
have noticed anything more than that.  So it's somewhat significant... 
but the more interesting question is, is it useful?

The answer is YES.  In theory, the magnetic WD spins "up" (period 
decreasing) when in a high-accretion state, and spins down in a 
low-accretion state.  Of course, HOW LOW is an important and probably 
unanswerable question.  But we do the best we can!  In this case, we can 
track spin-up/down by studying the 21-minute signal, which is strong as 
ever.  The fainter the star, and the longer the duration of faintness, 
the more convincing is this test.

Northern observers are now favored, because of the long nights.  Another 
month of coverage would be great.  Our usual advice of "not more than 
2.0 airmasses" doesn't quite apply here, since we're tracking a 21 
minute signal.  On a clear night, you can probably stretch it out to 3.0 
airmasses.  Beyond that, you're almost certainly in the regime of "bad 
data driving out the good".

No one biting yet on DN Gem.  This is likely to be a real winner!

joe
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