[vsnet-chat 5689] re CK Ori and W Ori tonight

[jg@jgws.freeisp.co.uk]

Doug West noted:

> Sebastian wrote:
> 
> <And for Pat, I also confirm his observation of W Ori still at
>   5.8. It is
>   very quiet now.>
> 
> I downloaded all of the W Ori observations from VSNET and performed some
> simple analysis to try to better understand the visual observations of
> this giant carbon star.  The observations I looked at ran from January
> 1946 to December 2001.  A plot of the observations revealed multiperiodic
> behavior.  I used various moving averages to filter the observations. 
> Plotting the observations I measured part of the time between peaks with
> the following results: 140, 670, 682, 391, 407, 408, 363, 413, 973, 671,
> 469, 729, 399, and 617 days.  The GCVS gives a period of 212 days.  It
> could be argued that most of the times between maxima correspond roughly
> to a multiple of the 212 day GCVS period.  The average for the over 7000
> observations was 6.51 and the standard deviation was 0.37 magnitude. 
> Taking three standard deviations either side of the mean gives a visual
> range of 5.40 to 7.62.  W Ori is definitely near a maximum.
> 
> Regards,
> Doug West

Also to be noted is that W Ori was likely at maximum in its long cycle
roughly a year ago, too.  I estimate the long cycle as being about 2360
days using AFOEV data to hand, whilst Houk in AJ 68, 253 (1963)
[adsabs.harvard.edu for downloadable copy] reckoned 2450 days.  I
derived time of 'twin maximum' from the same AFOEV data, and the last
subsequent time of long cycle maximum would have been about 330 days
ago.

Also folk should assess seasonal objects whilst also in consideration of
missed maxima, both at long and short cycle.  We may be in one of the
times when the short cycle, long cycle and seasonal suitability of
observation have all aligned to make maximum more notable than usual.


There are many LPVs with longer cycles of ten to twelve to thirteen
times the nominal period.  Houk listed many in her paper, actually the
publication of her doctoral thesis, in 1963, whilst Cecilia
Payne-Gaposchkin had already noted the matter in the early 1950s'.

This is much ignored nowadays, though they are real, with some notable
exceptions (eg papers by Kiss et al). I stumbled across it myself some
time ago, only to find it was well, if not widely, known.

The coincidence of time scale with the typical rotation period for such
objects is always enigmatic, but observational means of proof is
something else.


Cheers


John Greaves

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