(cba:news) Hercules novae... and AM CVn (Jonathan Kemp) [2025-04-27T19:00:30Z]

---------- Forwarded message ----------
Date: Sun, 27 Apr 2025 14:18:58
From: Joe Patterson <jop@xxxxxxxxxxxxxxxxxx>
To: cba-news@xxxxxxxxxxx
Subject: Hercules novae... and AM CVn

Hi CBAers,

Three Hercules novae deserve special mention now.

V1674 Her is back to pulsating strongly, at V~17.6.  Geof Stone and Richard Sabo
have been getting great data, even with some morning moonlight to fight.  Now
that the Moon has moved out of the way, it's a great time to observe it, if you
can handle the faintness.  Remember, it's just the phase of the 500 s PULSE we
mainly care about, so the S/N of each integration is not that important.

DQ Her.  Same general deal, except that the pulse is 71 s - so a short
integration time is mandatory.  Not necessarily <<71 s (because after the
analysis, each point counts at the CENTER of the integration), but short (maybe
<30 s).  Special note: drops to V~17.7 in mid-eclipse, at which point a close-in
neighbor is equally bright... so take suitable caution there (which might mean
"use generous aperture").

V533 Her.  Not seen to pulse since 1981.  But hardly ever looked for since then,
too.  It's the Search for the Lost Dutchman Mine.

AM CVn.  Still a fine target, and will be throughout May as well.  At 14.2 and
with no threatening neighbors, an easy target.  Here's the deal: the 1051 s
signal (superhump) and 1011 s (negative superhump) are relatively
straightforward... but the really interesting signal is the 1028.7 s orbital
signal - and to detect it, you almost always have to subtract the two stronger
signals.  This is a good target for a smaller scope which can cover the star
over a string of consecutive nights [of course, bigger aperture helps, but you
do have the subtract the superhumps to get at the underlying (weaker) orbital
signal].

V1223 Sgr.  Great southern target.  Main mystery is the reason for the pulse
period increase - but the truth is that we just haven't observed it enough!

joe

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