[vsnet-newvar 1320] Re: suspected variable near M31

[Seiichi Yoshida <comet@aerith.net>]

Dear Maciej,

I have some questions on AFA suspected variables posted to
vsnet-newvar.

> Subject: [vsnet-newvar 1213] Suspected variable AFASV_M31_33 (AFA images)
> AFASV_M31_33 amplitude=0.73         
> mag       R. A.  (2000)  Decl.   image
> 15.12  0 38 49.214 + 41 16 25.57 so1
> 14.59  0 38 49.378 + 41 16 35.17 ugm

There are some stars whose R.A. and Decl. on two images are very
different. I wonder why. And I would like to know the "true" R.A. and
Decl. of them to be added to the Taichi Kato's "newvar.cat" list.

> Subject: [vsnet-newvar 1261] Suspected variable AFASV_M31_442 (AFA images)
> AFASV_M31_442 amplitude=0.79         
> mag      RA    (2000)   Decl.   image
> 15.95 0 44 44.919 + 41 13 12.93 so1
> 15.16 0 44 45.057 + 41 13 34.14 ugm

The 21-arcsec difference seems too large for me. Is it really the same
star?

> Subject: [vsnet-newvar 1213] Suspected variable AFASV_M31_33 (AFA images)
> AFASV_M31_33 amplitude=0.73         
> mag       R. A.  (2000)  Decl.   image
> 15.12  0 38 49.214 + 41 16 25.57 so1
> 14.59  0 38 49.378 + 41 16 35.17 ugm
(snip)
> USNO A2.0:
> RA: 00 38 49.365 
> Decl: +41 16 35.33 
(snip)
> GSC:
> 00 39 00.00 
> +41 16 03.8 

There seem to be some mis-identifications in your list. The position
difference between the USNO-A2.0 and GSC data are too large to be the
same in the above case, for example.

> Subject: [vsnet-newvar 1219] Suspected variable AFASV_M31_99 (AFA images)
> AFASV_M31_99 amplitude=0.56 
> mag     R. A.  (2000)  Decl.    image          
> 15.30 0 39 37.307 + 41 41 29.49 ugm
> 15.86 0 39 37.356 + 41 41 29.45 so1
(snip)
> so1:  Mauro Facchini, Obsservatorio di Cavezzo, 
>       0.20- m reflector f2.8, CCD Starlight HX516
>       date: 26/06/00 time: 00:15:26 UT
> 
> ugm:  Mauro Facchini, Obsservatorio di Cavezzo, 
>       0.13- m reflector f4, CCD Starlight HX516
>       date: 06/09/00 time: 00:40:00 UT

We the MISAO Project also have many CCD images with similar
instruments. In my experience, the magnitude of faint stars around 15
mag measured from those CCD images often differs about 0.1-0.5 mag,
even if they are constant. So I only select stars brighter than about
13.5 mag with magnitude range larger than about 0.5 mag as real
variable stars when the images contain down to about 15 or 16 mag
stars. The 15-mag stars are not too faint on your images?

> Subject: [vsnet-newvar 1291] Suspected variable AFASV_M65_3
> AFASV_M65_3 amplitde=0.37
> mag      RA    (2000)   Decl.   image
> 16.66 11 18 34.132 + 13 6 05.46 test
> 16.29 11 18 34.141 + 13 6 05.28 kdm
> 
> images:
> test: P. Negrelli, Obsservatorio di Cavezzo, 
>       0.20- m reflector f2.8, CCD Starlight HX516
>       date: 22/04/98 time: ~20.5 UT
> 
> kdm:  Robert Trabatti, Stazione Astronomica Descartes, Italy, 
>       0.15- m Newton reflector f5, HISYS 23 KAF401E CCD
>       date: 17/04/01 time: 19:35:49 UT

Does the Starlight HX516 CCD use the KAF-0401E chip? When the chip is
different, there must be many stars whose measured magnitude become
different, even if they are constant.

Best regards,

--
Seiichi Yoshida
comet@aerith.net
http://vsnet.aerith.net/

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