[vsnet-chat 3679] re T Cas

[crawl@zoom.co.uk]

Taking P0 as 444 days, and P1 as 222 days [and I can't be bothered to argue
as to whether this is "doubly periodic pulsation" or merely a fourier
harmonic artefact due to T Cas' lightcurve being strongly non-sinusoidal],
then the _amplitude_ at P0 and the _amplitude_ at P1 cycle in an
approximately 2800 day period.  Equally, phi21 of T Cas over time, which is
the difference between the evolution of P0's phase over time from that of
P1 over time [or vice versa] also undergoes a cyclicity of about this
level.  These need to be found via the _autocorrelation function_ of
amplitude over time and/or phase difference over time, as these are too
non-sinusoidal to be viewed with DFT.

Now, T Cas is a longish period Mira with a "hump" on the rising branch of
the lightcurve.  Sometimes this hump is pronounced and discrete causing a
"dip" to be apparent twixt the hump and maximum, sometimes it "merges" with
the maximum which is thereby reduced in value, and becomes more spread out.

What the first paragraph above is saying is that this phenomenon occurs on
a repeatable level of around every 2800 days.


At present, and coincidentally, the chewy workings out of this result is up
in the air as the paper presented several months ago to a professional
journal is being re-refereed.  The first referee insisted that the analysis
should utilise "wavelet analysis" which analyses frequency behaviour over
time, whereas the "ampscan" procedure used is fundamentally flawed due to
relying on analysing phase behaviour over time.

As phase and frequency are integral and differential of each other, any
"fault" ampscan methodology is purported to suffer is therefore equally
true of wavelet analysis.

I hope to stop swearing over this soon...

Anyway, it'd be interesting to see what values you come up with, if any,
from your correlation measures.  Don't let the above 2800 day period bias
you... ...it is just one opinion.  I can show one for just over 3000 days
for chi Cyg too, though not as cleanly.

Meanwhile, both the online AFOEV archive and the online VSOLJ archive have
large amounts of data for T Cas, going back a long way. 


Cheers

John

John Greaves
UK

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