[vsnet-chat 5423] Re: (fwd) V4641 Sgr identification ondifferent sources

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

Dear readers and observers of exciting objects,

The posted image shows typical relative star brightnesses from
unfiltered CCD observations and is quite informative for those that are
uncertain about the V4641 Sgr position.

Just in case someone is interested. For my timeseries I have used the
following reference stars to V4641 Sgr:

comparison star C: not indicated by marks but it is the bright star
South of '90'. It is 9.4R (and 9.9V). 
alternative C (for longer than 10 sec exposures): the isolated star to
the WSW of '93'. It is about 11.2R (11.6V)

These stars are reasonably blue (white-) and conveniently situated. 

My checkstar K is the nearby star NNW of V4641 Sgr and of (very)
similar R brightness. It is well isolated and the least red of the
neighbouring stars, despite its B-V>1.0 still. 
The (brightish) indicated nearby star (NNE of V4641 Sgr) has a B-V of
about 2.0, which makes it a bad choice for K. At 13.6 V it is visibly
fainter than V4641 Sgr, most of the time!!

I am still puzzled to which star Mr Scarmato has been looking at.
Hopefully he will let us in on his secret.....

Kind regards (and hopefully no offence),

Berto Monard
Bronberg Observatory




>>> Taichi Kato <tkato@kusastro.kyoto-u.ac.jp> 07/26/02 05:18AM >>>
(fwd) V4641 Sgr identification on different sources

   I forward this message here because this is likely of public
interest:

---

just to identify - not to do photometry - I took an image of V4641 Sgr
on
08. April .2002. I did not use any filter. The only goal was to
identify
the object. During my first attempts to identify, I used the AAVSO
chart
1813-25B (prelim. E) v. 11/99 and thought that the blue labelled star
was
V4641 Sgr. In SIMBAD I could identify the red labelled star. And with
the
two images from your Website I became sure that SIMBAD is right. 

I posted my problems in the German BAV mailing list and sent an eMail
to
the AAVSO. The cannot do anything without a V filtered image. The BAV
recommended to send the image to you, Sir.

2002-04-08 12:01:27 UTC, 08.04.02 5:58 MDT, exposure 180 s, 16inch
Meade
SCT with Focal Reducer and ST-9E, no filters. 

I do not have any requests for your response. I got the star. You may
include my image in your Website. If you want, I can send you the
image
without labels and text. 

Kind regards
Hans G. Diederich
www.HansGuenterDiederich.de 

---

   The image is placed at:

  
http://vsnet.kusastro.kyoto-u.ac.jp/pub/vsnet/Xray/GM_Sgr/Diederich.gif

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