[vsnet-chat 4438] Re: re R Hya

[crawl@zoom.co.uk]

At 09:21 12/05/01 +1200, Stan Walker wrote:

>Hallo John,
>
>I presume that I have the same VSOLJ dataset from VSNet that you used.

Hi Stan

The VSOLJ data I've got for this star is by far the lesser amount.  I've
mostly got BAAVSS and AAVSO data for this star, acquired ages back [on a
floppy via airmail for aavso if I remember rightly!].  It'd be a good
assumption that both of these datasets have a lot of RASNZVSS stuff in
them, probably the same stuff!  I did the exercise independently on BAAVSS
data to start, then independently on AAVSO data when it turned up, as a check.

>This reflects on your other comment - that the period has stopped
>decreasing. I've searched the data for periods but the results are
>equivocal. There is a spread of periods from 410 to 384 days which could
>support both cases. At present I'm trying to get hold of a dataset from one
>of our people who has looked at R Hydrae for a long time and whose data is
>usually top class. You get better results from using a single prolific
>observer's measures. Maybe Sebastian could get hold of something like this
>in South America?

Split your datasets into two bunches either side of 1940 and DFT them
separately.

The profiles and widths of the main peaks will show you which periodicities
at which epochs are "tighter", although unfortunately there isn't too much
data pre-1940 in the electronic archives [goes back to 1920ish I think],
and this in itself can cause broadening of peaks.  Works best if you have
the times of maxima going back for quite some time, then you do an O-C pre
1940 and a separate one post-1940... ...the 1st will give you a goodish
parabola of largish residual range, the 2nd won't.


General question... ...what is the difference between "Helium shell flash"
as hypothesized for period changing Miras a la the original Wood and Zarro
model, and "Helium shell flash" for objects like FG Sge or Sakura's
Object!?!?!?!  This has always confused me, as the two types of star are
quite different and the two types of displayed phenomena are quite
different too, yet they are accused of undergoing the same sort of event.
Or is it that FG Sge is commencing Helium _core_ burning????

Cheers

John

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