[vsnet-campaign-v4641sgr 63] Re: [AAVSO-DIS] V4641 Sgr - Very Active

["Berto Monard" <LAGMonar@csir.co.za>]

Hi Michael, 

I always like it that someone takes it up for visual observing. Let me
tell you that I am on your site here! 

The possible very short term flickering by this enigmatic star is very
difficult to measure at the subscond level though. And unfortunately the
eye cannot give precise descriptive detail of short term light
fluctuations. 

To visually observe V4641 Sgr before a run is sometimes quite
difficult. At about 12 deg above the horizon, and presently staring in
the direction of the full moon, that is not going to be helpful, but the
CCD camera will get results from that position. 

Something that might interest you: I am not certain (it can be checked
though), but I think that I might have made the most number of positive
visual observations of V4641 Sgr since 1999 (only one per night allowed)
...

Regards,

Berto Monard
Bronberg Observatory



>>> Michael Linnolt <linnolt@hawaii.edu> 05/25/02 03:16AM >>>
The msec variations observed visually are indeed real. My observations
were made with at least 2 comps simultaneously visible in my visual
field.
The 123 comp is so close that both it and V4641 are in my foveal area
and
receive the highest, and equal attention. V4641 clearly varied
dramatically compared to the more steady comp. There was of course
almospheric effects as well as vision variations that affected the
comp,
but the relative difference between the target and comp was so obvious
there is no question
about the variability.

Granted V4641 is a rare case, but this does show an extreme advantage
of
visual over CCD. In fact, had nobody bothered to look at this thing
through an eyepiece, its possible these ultra-short variations would
never
have been detected via CCD. Maybe evryone with telescope time should
devote 60 seconds looking at their target thru an eyepiece before
starting
their data runs ;)

Mike Linnolt

 On Fri, 24 May 2002, Berto Monard wrote:

> I think that would be a great idea even if it were (only) to prove
that
> the perceived msec variations might be eyevision-induced or caused
by
> atmospheric turbulence......
>
> Great system, V4641 Sgr! A pity I made a booboo last night..
>
> Regards,
>
> Berto
> Bronberg Observatory
> Pretoria
>
> >>> Michael Linnolt <linnolt@hawaii.edu> 05/24/02 12:31AM >>>
> Beware of drawing conclusions from "short term" variations in this
> star
> using CCD. The fluctuations are so rapid that even fast photometry
> with
> 1sec exposures and 2.5sec integrations wont catch them faithfully.
> Visual
> observations show the true behavior here. To compare favorably, CCD
> would
> need somewhere around 0.1-0.2sec integration times, and continuous
> monitoring without gaps. Essentially you need video recording
> equipment.
>
> I would recommend someone just hook up a DV camera or camcorder to a
> good
> size observatory class instrument and record several minutes of the
> stars
> behavior for a true reference of its variability.
>
> Mike Linnolt (LMK)
> Honolulu, HI
>> aavso-discussion@mailman.McMaster.CA 
> http://mailman.McMaster.CA/mailman/listinfo/aavso-discussion 
>
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