[vsnet-chat 4434] re R Hya

[crawl@zoom.co.uk]

Hiya Sebastian

If you look at the vsnet image archive you'll find a plot of the long term
phase and amplitude behaviour for R Hya going back about 90 years which
vaguely suggests some quasiperiodic long term variation in amplitude, but I
wouldn't swear to it.

[http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/Mail/vsnet-image/msg00038.html]

The x axis is JD -2400000, the left hand y axis is phase in degrees and the
right hand y axis is semi-amplitude in magnitudes.

The red symbols are semiamplitude over time keyed to the right y axis based
on John Howarth's ampscan procedure, whilst the blue symbols are the same
but generated by Grant Foster's inculcation of wavelet analysis.  Although
the latter looks "neater", this is primarily because the wavelet analysis
technique is of a far higher computational load than the ampscan technique,
and therefore the data was sampled at a far lower resolution.  The ampscan
data is probably more detailed.

The black crosses, by the way, are phase over time.

As you can see, the monotonic period decrease of R Hya ceased around 1940,
with period variation within this star being more or less stochastic about
a mean since then.  Of large import is that mean semiamplitude also dropped
markedly about this time.

Some detailed discussion on the behaviour of R Hya periodicity and light
curve can be found in part of the following article [despite the article
being primarily about W Dra], although not much on the amplitude really

http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=2000JAVSO..28..
.18G&db_key=AST&page_ind=4&plate_select=NO&data_type=GIF&type=SCREEN_GIF

(this url will have been word wrapped on transmittal, unwrap it afore usage)

I never did publish the analysis on this star, but it is interesting to
note that professional papers will still seriously quote it as being
decreasing in period, and a prime example of such behaviour, even though it
ain't true and hasn't been for sixty years.

This star has displayed some interesting behaviour over time, and if the
inherent morphology of the lightcurve has undergone a fundamental change,
as suggested by your post, something interesting is occuring.

A good one for visual observers to keep following, extending the already
extant long baseline visual database into the depths of the current century.

[Data used in the analysis is from BAAVSS, AFOEV, VSOLJ and AAVSO, both
independently assessed and as merged etc, &c.  BAAVSS data includes
RASNZVSS data due to a reciprocation agreement on certain common near
equatorial stars.  No doubt AAVSO data also contains RASNZVSS data as a
subset due to a similar agreement. Everybody are the respective owners of
what belongs to them.]

Cheers

John

[PS  Anybody got that data request engine at the aavso website to
work!?!?!?!?  I haven't got the damn thing to cough up any data in well
over a year of trying, despite several requests, and unanswered querying
emails re non-receipt!  Maybe they don't love me no more!?].

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