[vsnet-chat 3607] re Periods of roughly one year

[crawl@zoom.co.uk]

Michael Dahm wrote:

> It seems to be that this red giant distributed in all directions of our
Milky Way prefer a period of  > nearly 365 days or one terrestical year. Of
course this must be a result of spurious periods.

Indeed, these "annual signals" usually readily show up in the weighted
"spectral windows", but are sometimes quite evident in just normal power
spectra when the source data is very sparse, and even more so when the
object under investigation is quite seasonal, when you get an annual gap in
the data.

> Checking periods of not well covered low amplitude semiregular variable
stars does not 
> confirm reported period values. This seems to be an interessting field
for amateurs doing 
> some kind of quality controll.

Ah, Michael, you are too modest!  You are actually discovering the true
periods of these objects for the first time!  The original analyses were
probably based on a scattering of photographic survey plates taken over
many years, with no guaranteed maxima amongst them.

It is more than 'quality control', you are actually providing periods for
known GCVS objects that have effectively not had them before.  Although an
entry may exist in the GCVS for periods for some variables, sometimes these
are in effect no more meaningful than if the period entry had been left blank.

.......

Also, a small correction, you wrote:

> also in Tycho-2 data.

it was actually Epoch Photometry Annex A data from the original Tycho release.

Cheers

John

JG, UK

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