[vsnet-chat 4700] Re: re Bernhard Variable 92

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

Hi John & Klaus,

Good to see a change of pace with all this news about WZ Sagittae. I noted
the comment about SARVs and wondered what length periods you were getting.
Harry Williams and I made some measures of SARVs some years ago but, quite
frankly, the observing methods to be used were not particularly reliable and
the results were confusing. If you're achieving 1-2% photometry then it's
hard to be certain about amplitudes of less than 0.1 magnitudes as many of
these SARV candidates seem to have. We couldn't even confirm the periods on
some of the more well known of these objects. With target star, comparison
and check all early M class probably everything was varying. With better
comparisons and colour transformations the results would probably have been
better but this wasn't under our control.

The other thing which disappointed me was that many of these stars ended up
in the GCVS as SR stars. In the old days SR stars were longish period
(50-500 days) with reasonable amplitudes (0.5 to 5.0 magnitudes). The light
curves were indeed, semi-regular, usually because there were several
simultaneous pulsation periods. But now, anything variable goes in this
class.

The other thing we noticed was that almost all late K and M stars were
variable over a longish time scale. Probably spotted, although at Mt John
one observer found low amplitude radial velocity variations. In those days
the IBVS seemed more rigorous than now, so noone at Auckland bothered to
follow up all these stars. If everyone did the GCVS could probably be
expanded by
a few hundred thousand stars! So, whilst I didn't like the programme much,
there is probably some value in creating a new classification - SARV - in
which probably all non-Mira nd non-SR or non-LPV - red giant stars fit.
Incidentally, LPV seems another misnomer. Probably the stars here are mostly
SR with not enough reliable measures.

As not all the discussion seems to be on email I may have misinterpreted
what is being said. But since there are some extremely interesting objects
amongst the larger amplitude SR stars it's frustrating to see the SR
category used as a sort of 'unclassified' dumping place. Maybe there is a
case for an unclassified variable type? To my mind SARVs are SARVs and not
SR stars.

Regards,
Stan

----- Original Message -----
From: Klaus Bernhard <kl.bernhard@aon.at>
To: <crawl@zoom.co.uk>
Cc: <vsnet-chat@kusastro.kyoto-u.ac.jp>
Sent: Sunday, August 05, 2001 4:45 AM
Subject: [vsnet-chat 4689] Re: re Bernhard Variable 92


> Hi John,
>
> at the beginning of my survey members of BAV and I have made additional
> observations of a few new "SR"-variables (for example
> GSC 1062-92, IBVS 4540). All of them turned out to show cyclic
> variations, of the kind which is described in the IBVS 5041 about
> 25 SARVs.
> Except of one, BrhV89, all other "SR" variables showed variations
> during the 1-2 months of survey-observations, which could be interpreted
> as parts of sinusoidal variations, but I know this is a rather
> "weak" argument.
> So it seems that irregular variability of type "L" is rather the
> exception for those small amplitude red variables, which I found
> during my survey.
> Of course I recognised also some red variables with larger amplitudes,
> but all were known Mira variables.
> Because this preliminary description "SR" is also accepted by IBVS,
> I see no really problem to use it at the moment.
> And finally there exist some other examples even for short period
variables,
> which are publicated and taken into GCVS without known
> periods (example: the RR-Lyrae variable V576 Her).
>
> But I have to say, that this is only my personal view as an
> amateur astronomer and not as an expert in red variables.
> I would have no problem to use other preliminary descriptions for
> such red variables, if it is necessary.
>
> Best wishes,
>
> Klaus Bernhard
>
>
> crawl@zoom.co.uk schrieb:
> >
> > Hi Klaus, et al
> >
> > Unfortunately there is a predilection in many quarters nowadays to class

> > stars as type SR without any indication whatosever of cyclicity within
the
> > data.
> >
> > Most people are classifying stars as SR when they should be classifying
> > them as L ... ...in fact in some cases, where no hint whatsoever of any
> > form of colour information exists, or the colour is around or equivalent
to
> > B-V of about 1 ish, the objects should simply be classed type I.
> >
> > It should also be noted that although type L is a bit of a grabbag class
> > for objects that are not as yet sufficiently studied to be able to be
more
> > properly classified, there are some LPVs with well known lightcurves
that
> > actually remain type L because they show no regularity, whether full or
> > semi, within their behaviour.  (Trouble is, I can't remember one offhand
:( )
> >
> > As I've said before, a high amplitude slowly varying red star is nearly
> > always going to be a Mira, though I suppose there's always a chance of
an
> > RCB star being stumbled across, but a low amplitude slowly varying red
star
> > can be one of several things, even if evidently an LPV.
> >
> > Variant opinions welcome.
> >
> > Cheers
> >
> > John
> >
> > John Greaves
> > UK
> >
> > At 20:19 02/08/01 -0700, Klaus Bernhard wrote:
> > >Dear John, Dear colleagues,
> > >
> > >I also think, that both indications (B-R from USNO A2.0 and the
> > >apparently slow variation, deduced from about 10 observations
> > >in different nights within 1-2 months), which I take for classification
> > >as a "SR"-variable are not unambigous.
> > >If a "SR"-variable would be in fact a short period variable,
> > >there could arise wrong B-R values, even if the epochs of the plates
> > >differ only few days.
> > >So I always mention in the VSNET-postings, that the colour and the
> > >apparently slow change in brightness "suggest" a SR-variable.
> > >
> > >But I see, especially because of the X-ray source BrhV84
> > >(a "SR-variable" transformed in a likely short period variable) that I
> > have to write instead of
> > >"Other types of l o n g period variability cannot be excluded"
> > >in future
> > >"Other types of variability cannot be excluded"
> > >in my VSNET-postings.
> > >
> > >Best wishes,
> > >
> > >Klaus Bernhard
> > >
> > >>
> > >> The epochs of the USNO A2.0 plates that this variable appears upon
are
> > >> dated 1979 for the blue one and 1984 for the red one.
> > >>
> > >> Using magnitudes from two totally different epochs for an avowedly
variable
> > >> object in an attempt to decide a colour index and subsequently a
> > >> variability class is a somewhat problematic exercise.
> > >>
> > >> John
> > >
> > >
>

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