(cba:news) AM CVn, in particular (Jonathan Kemp) [2025-04-30T17:40:38Z]

---------- Forwarded message ----------
Date: Wed, 30 Apr 2025 13:35:12
From: Joe Patterson <jop@xxxxxxxxxxxxxxxxxx>
To: cba-news@xxxxxxxxxxx
Subject: AM CVn, in particular

Hi CBAers,

Recent coverage of AM CVn (Joe Ilowetz, Dave Messier, Geof Stone, David Cejudo,
and others) suggest that we might finally nail down the secrets of this famous
helium star.  First, read the previous papers to see why it's so famous
(17-minute binary!,,, the first "ultrashort" known - there are still only a
few).

At a recent Ontario (CA) conference, we "published" a paper claiming to know the
exact period structure.  I say "published" because I don't know for sure if it
came out in "cite-able" form... and I say "claiming" because I don't know if we
really proved it.  Here's what we said:

1. The main period is 1051.2 s, with much of its power at the first harmonic
(525.6).  This has been known for 50 years.

2. A second signal exists at 1011.4 s - known for ~20 years.

3.  The 1051 guy is definitely not stable in phase (therefore not = Porb).  The
1011 guy is also probably unstable, though I can't recall if anyone has proved
that.

In the conference paper, we took the CBA data during 1978-2019 and subtracted
the 1051 s signal from each year (easy), then subtracted the residual 1011 s
signal (questionable, because somewhat transient).  The result was a
well-defined 1028.73 s signal, which decreased in period. The natural
interpretation of this is the TRUE orbital period - no longer confused by the
damn superhumps!!

Two white dwarfs in very close orbit are a test of GR.  Not as good as the
binary-pulsar test, and a few others.  Maybe to put it better, GR + this result
can constrain the individual masses in AM CVn - IF we can confirm (or otherwise
measure) the proposed 1978-2019 period-decrease rate.

Finally, can anyone (Bob Stephens maybe?) point me to a publication where I
first presented this?

joe

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