[vsnet-campaign-v4641sgr 38] Re: [AAVSO-DIS] V4641 Sgr - Very Active

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

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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