[vsnet-chat 5349] More on UY Cen fading

["Sebastian Otero" <varsao@fullzero.com.ar>]

----- Original Message -----
From: "Michael Poxon" <m.poxon@virgin.net>
To: "Sebastian Otero" <varsao@fullzero.com.ar>
Sent: Tuesday, June 11, 2002 4:52 PM
Subject: Re: [vsnet-campaign-rcb 40] Re: [vsnet-chat 5346] Re: On UY Cen
fading


> Have I misinterpreted something here, or is someone using an 8" scope to
> observe what looks like a binocular-magnitude variable, and a deep red
star
> at that? If so, small wonder that folks are getting weird results! Even at
a
> mag.10 minimum, an 8" objective (unless there's a fearsome amount of light
> pollution, which will anyway play havoc with coloured stars) seems to be a
> bit too large for a star like this.

Dear Michael:

Besides light pollution and star's colour, I can't see a 9th magnitude star
through my 7x50's.
At magnitude 8.5 - 9.1, UY Centauri is a perfect target for my 8".
Your comment would apply to objects brighter than 8th magnitude from my
observing site.
It all depends on the limitting magnitude you have. My sky is around
magnitude 5.3 (naked eye) and my binoculars can see almost down to 9.0.
Observing a red variable at the limit of your instrument is not desirable.
In spite that you will probably don't catch it since limitting magnitude use
to refer to the faintest star visible using averted vision (blue and white
stars).
Red stars are hard to detect at the limit because rods are color-blind.
A general advise is to estimate stars between 1 and 3 magnitudes brighter
than your limitting magnitude.
For my use those values would be:

Naked eye:   lim. mag. = 5.3
BEST RESULTS =  1.3 - 4.3 (and that's true)

7x50's:  lim. mag. =  9.0
BEST RESULTS =  5.0 - 8.0  (and that's true)

8":  lim. mag. =  12.5
BEST RESULTS =  8.5 - 11.5 (and that's true)

UY Centauri now is around 9th magnitude and I can't detect it with
binoculars (red star limitting magnitude is probably around 8.5). It is a
very good target for my telescope. Comparison stars fall in the same field
with my 40mm eyepiece (almost a degree of field of view).
No complication is estimating it besides its deep red color. That is what
may bother our work.

So, as a conclussion, UY Centauri USED TO BE a binocular variable but it's
not a binocular variable nowadays.

Regards,
Sebastian



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