[Aavso-photometry] SU TAU

[Arne Henden]

Bruce Sumner has a good sequence for this field, based on my photometry:
   ftp://ftp.nofs.navy.mil/pub/outgoing/aah/sequence/sumner/sutau.seq
This was used as the basis of the F-scale chart for the AAVSO.
The variable is at
   05 49 03.73  +19 04 21.9  (J2000)
using my astrometry, in agreement with VizieR.  As Bruce mentions:

1. There is a bright double star located 1.1 arcmin west of the variable
with components of about magnitude 11 and magnitude 12. The separation is
about 8 arcsec. At low magnification, when the individual components
cannot be seen, this star has a composite magnitude of V=10.42+/-0.01.
It is not suitable for use as a comparison star.

This may be the 10.11 "star" mentioned by Brian.  You can check whether
you have the correct identification of the variable by observing either
with two filters, or with the V filter and unfiltered.  RCrB stars
are very red.  I did a lot of RCrB calibrations for Bruce, though
it is not a class of star that I personally study.

Arne

Radu Corlan wrote:
> On Mon, 27 Dec 2004, Brian C. Barnes wrote:
> 
> 
>>I've recently added SU TAU to my list of variables I'm monitoring. The AAVSO
>>chart (SE0401) lists SU TAU as 05 49 03.7, +19 04 22 (J2000.0), with a
>>rather bright (but unlabeled) star to the NW. At the given location I've
>>found a rather bright star, of approx. 10.11 MagV. I've noticed that lots of
>>folks have submitted observations for this star. My problem is that,
>>according to my copy of the GCVS, SU TAU is actually at 05:49:23.37, +19 04
>>04.78, south and east of this brighter star. According to photometry of my
>>image, at the GCVS location is a star, but it is too dim in my image (20
>>seconds) to get any MagV data on - my dimmest star is MagV 15.83 +- ~.5.
>>
>>So my question is, is the AAVSO chart correct and the GCVS catalog is wrong,
>>or is the GCVS correct, and lots of folks have been submitting observations
>>for the wrong star? I'd like to be certain of my data.
> 
> 
> GCVS is wrong on this one. The star is the one at 05:49:39.40 +19:04:21.9 
> (Tycho/GSC 1307-1573). I have 10 images of this field (earliest from 
> sept 2003) and can see it vary several magnitudes.
>