[vsnet-campaign-v4641sgr 42] Re: [AAVSO-DIS] V4641 Sgr - Very Active

[Michael Linnolt <linnolt@hawaii.edu>]

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
>
> On Thu, 23 May 2002 DWest61506@aol.com wrote:
>
> > If you haven't been observing V4641 Srg (1813-25B) lately you might
> want to take a look.  I don't remember observing a star, or X-ray binary
> (microquasar) in this case, that varies in magnitude so rapidly.  On the
> 22nd UT, I measured a change using an unfiltered CCD of greater than 0.6
> magnitude in 20 minutes (see the Quick Look file).  This wasn't just a
> noisy measurement, my check star's standard deviation was only 0.03
> magnitude.  The magnitude range in the last few days has been from 11.5
> to 13.
> >
> > Regards,
> > Doug West (WJD)
> >
>
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