[vsnet-chat 3524] Re: The difference between Mira and SRa

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

Hi Michael,

I noticed your question but have been a little too busy to think about what
you wrote until now.

I'm always interested in anything to do with Miras and semi-regulars, so
would appreciate a copy of any of your conclusions.

I was analysing visual data of about 80 southern stars which ostensibly were
Miras. My conclusions were that most stars with periods under 200 days were
probably not Miras but were supergiant stars and as such should be
classified as SR stars. But here the problem arises - many SR stars have
amplitudes larger than 2.5 magnitudes. As a group Miras seem to pulsate with
only one period at any moment - SR stars usually have two or more periods
which beat, hence the lack of regularity.

More recently a large number of M giant stars have been called SR stars but
after making pep observations of some of these I think they should be called
irregular - the amplitudes and periods are all over the place! And in the
past anything which was red and didn't fit anywhere else was called SR by
default!

To complicate the issue, some SR stars seem to be very regular. T Centauri
is one such, with a large amplitude as well. Why it was called an SR star is
anyone's guess. But the amplitude of alternate cycles varies so that it
seems that 181 days is the true period - not 90.5 days.

In conclusion, I would think that if it has a period of 300 days it's
probably a Mira star. But check for secondary, even tertiary, periods using
a good period search programme. If these are there, it's not a Mira.

Regards,
Stan


----- Original Message -----
From: Dahm, Michael <marvin.siriuscorp@planet-interkom.de>
To: chat VSNET <vsnet-chat@kusastro.kyoto-u.ac.jp>
Sent: Monday, July 31, 2000 4:48 PM
Subject: [vsnet-chat 3510] The difference between Mira and SRa


> Hallo!
>
> As byproduct of an investigation of EF Aql I have a question about the
> difference between Mira and SRa stars. EF Aql is a red longperiod variable
> with a period of 300 days. But the classification is rather difficult.
>
> SRa and Mira stars are red longperiodic variables and the borderline
between
> them is the amplitude of 2,5 magnitude (mean amplitude or the observed
> extrem values?). There is also no definition about the passband but the
> amplitude is greater at shorter wavelength and rather small in the
infrared.
>
> A further question : Does it make sense do separate between SRa and Mira
> stars or do these stars have the same physical parameters except of their
> amplitude? I read once that stars evolve up and down the AGB (Lb > SRb >
SRa
> > Mira > SRa > SRb > Lb and again and again)
>
>
> Michael Dahm
> Email : marvin.siriuscorp@planet-interkom.de
> Homepage : www.planet-interkom.de/marvin.siriuscorp/
>
>

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