[vsnet-chat 1877] Re: Perplexing questions?

[Eric.Broens@advalvas.be (Eric Broens)]

Dear Justin and vsnet-colleagues,


>   Visual observations in themselves can be worth analyzing, using various
>mathematical techniques.  A survey of period changes in pulsating stars
>led to the discovery of the helium shell-flash effect, chaos has been
>searched in the long-term light curve of dwarf novae, and again many
>others.

An example of this is the study we made of chi Cygni.
5 years ago I gave a presentation during a meeting of the Variable Star
Section of the Vereniging Voor Sterrenkunde (a Belgian astronomical amateur
association).
I presented there an analyses of 25 years of observations made by the
Belgian observers. The O-C diagram looked interesting but the conclusion
was: a longer baselength of observations is needed.

I was very lucky that Dr. Chris Sterken of the University of Brussels (VUB)
was invited as a guest speaker. He encouraged me to find more observations
and even proposed to coerate to analyse the observations.

Via VSnet we asked for observations of chi Cygni. Makoto Watanabe of the
VSOLJ and Dave McAdam of the BAA VSS promptly sended us observations of chi
Cygni dating back to the beginning of this century! THANKS Makoto and Dave!
The O-C diagram now really looked very promissing and Dr. Sterken started to
look in old publications for even earlier observations. While he was
travelling to conferences and observatories he entered more than 4000
observations dating back till ... the discovery of Chi Cygni in 1686.

The O-C diagram now looked very spectacular.
Together with Dr. Koen of the South African Astronomical Observatory we
analysed the O-C diagram and found strong evidence for an linearly
increasing period by about 0.013 days per year (this is about 4 days since
the discovery date).
Amazing is that even very well know stars reveal such features.
So it is also worth it to keep on observing well known stars.

The study resulted in 3 papers, two of it deal with the discussion of the
observations and in the 3rd the analysis of the observations is discussed:

1) Long-term visual magnitude estimates of the Mira variable chi Cygni. I.
1686-1900
   Sterken C., Broens E.
   Journal of Astronomical Data, 1998, Volume 4, Number 7

2) Long-term visual magnitude estimates of the Mira variable chi Cygni. II.
1900-1998
   Broens E., Sterken C., McAdam D., Watanabe M.
   Journal of Astronomical Data, 1998, Volume 4, Number 8

3) On the period history of chi Cygni
   Sterken C., Broens E., Koen C.
   Astronomy and Astrophysics, v.342, p.167-172 (1999)
   (available from ADS)


I am very greatful to Dr. Sterken for making all this possible!

Best Regards,
Eric

The Journal of Astronomical Data (JAD), Volume 4, Number 8 (1998)
------------------------------------
VVS Werkgroep Veranderlijke Sterren

Eric Broens
Wateringstraat 143
B-2400 Mol
BELGIUM

E-Mail: Eric.Broens@advalvas.be
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