[vsnet-chat 3523] Re: R Cen...

["Stan Walker" <astroman@voyager.co.nz>]

Hi John,

R Centauri's period has been decreasing for all of the twentieth century.
But I was not aware that its amplitude was acting in a similar manner.
Whilst writing this message I've just checked the visual measures from JD
2423000 to 2443000 and see that they show no long term decline in amplitude.
Pep measures since then appear fairly normal but are a bit sparse.

There is a probable 5000 day variation - I don't know if anyone has picked
this up. R Cen has a blue companion which may affect it in some way - it
certainly lessens the amplitude a little. What's the second period you
mention?

BH Crucis is changing more dramatically than R Cen. Its period has gone from
421 days to well over 500 in a few decades. R Normae is not as well
observed, but shows two alternate periods as do many Miras. As I mentioned
to Peter Williams, I think that Miras with periods greater than 400 days are
in an unstable evolutionary phase and you can expect almost anything.

Regards,
Stan

----- Original Message -----
From: no name <crawl@zoom.co.uk>
To: <vsnet-chat@kusastro.kyoto-u.ac.jp>
Sent: Saturday, August 05, 2000 10:37 PM
Subject: [vsnet-chat 3520] R Cen...


> Dear southern hemisphere folk
>
> I have a bit of difficulty keeping up with literature on Southern
> variables, especially papers by amateur organisations.
>
> Basically, the [in]famous doubly periodic Mira star R Cen:
>
> has anybody noticed that _both_ its periods are steadily declining, as
> indeed are both its amplitudes, in a fairly systematic way?
>
> Indeed, given a few more years of amplitude reduction, instead of
> looking like an exotic double peaked Mira, it'll look like quite a few
> other doubly periodic SRb stars [though the period ratio is still a
> pretty solid 1.99, and ampl. about 3 mag].  Granted, that'll primarily
> be based on the arbitrary delimiter of 2.5 mag amplitude twixt Miras and
> SRs.
>
> Haven't seen a behaviour like it, except possibly when W Tau stopped
> behaving like a very regular single period SRa star in the early 30s and
> became a double periodic SRb star at that time, afore descending into
> the current near chaos of periodiocities. [Again, W Tau looked SRa, but
> would have been called a Mira if it hadn't been of only about 2 mag
> amplitude, which begs the question as to what the amplitude may have
> been of this object in the past.  There was a steady amplitude decrease
> up to the 30s "event", but there's only data back to just about the
> 20s].
>
> Finally, there's a handful of these "double peak" Miras visible from
> Southern climes.  Its a bugger getting hold of data for Southern
> hemisphere variables, but the few light curves I've managed to see show
> temporary double peaking, and stuff not that dissimilar to what T Cas
> and chi Cyg can get up to from time to time.
>
> R Cen is pretty unique though.  Another classed with it is R Normae.
> How similar is "our Normy" R Cen is lightcurve characteristics?
>
> Ta
>
> John
>

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