From: Mamoru Doi (doi@ioa.s.u-tokyo.ac.jp)
Date: Sun May 19 2002 - 19:09:05 PDT
Hi Chris,
We agree in 0.3arcsec levels, good.
I am not sure you and Naoki (who is unfortunately traveling) are
using 0-index or 1-index for coordinates, and I just write down
some notes on relative offsets.
Please note that the SN is about 2 pixel East of the April center
of the host. If you are using a global center including a host, the
real position may be slightly (1 pixel=0.2arcsec?) shifted toward East.
Central part of the Hex star is saturated, and signals in south-west
part of the PSF is taken away somehow, which could make normal
fitting code to give the answer with systematically north (+y) and
east (+x). I didn't use normal centering code and measured the center by
eye-ball fit.
These may explain our differences both in RA and Dec.
It seems to me that the Hex star is too bright for us to get precise
offset. Saul told me that you may have a better candidate.
I will measure offsets if you send me better reference star position
(in x and y).
-Mamoru
>
>Thanks for the image.
>
>Using this image and using the location of the cross in the finding chart
>which is quoted by Saul as
>the defining position for the supernova. I measure the candidate to be at
>
>x=908.86
>y=891.39
>
>I get the co-ordinate of the reference star to be at
>
>x=1021.21
>y=607.22
>
>Which, given the saturation is fine.
>
>Thus the disagreement comes from the quoted x position. At
>x=890.02, y=891.07, I see nothing,.
>
>Using x=908.86 and y=891.39, I get offsets of
>
>delta_ra=57.40
>delta_dec=-22.69
>
>and an angle of -68.43.
>
>Mamoru gives offsets of 57.75 , -22.40 and an angle of -68.80, and from the
>FORS2 acquisition image, I tend to
>agree with these number.
>
>Thus I will ask Paranal to observe this target with Mamoru's numbers.
>
>Cheers, Chris.
>
>
>>
>> According to Naoki, the position of the candidate on this field is
>> x = 890.92
>> y = 891.07
>>
>> Now, the hex star is a little difficult to work with because it is
>> saturated, but the best position I can fit for it (which at least
>> looks reasonable by eye) is
>> hex x = 1019.8436
>> y = 606.11876
>>
>> According to the plate scale encoded in the WCS in the header, this
>> gives an offset of (x is DEC, y is RA, scales 5.61140246764259E-5
>> and 5.61194595833103E-5)
>>
>> delta_ra = 57.568717
>> delta_dec= 26.043926
>>
>> arcseconds, where I've dropped all signs. This is in much closer
>> agreement to our value than to Mamoru's.
>>
>> So, I'm very puzzled by this. A 3" disagreement is 15 pixels, which
>> is enormous, and should show up easily by eye when I look at things
>> even roughly. Something is off here, and I don't know what.
>>
>> Alex
>>
>>
>------------------------------------------------------------------------------------------------------------------------------------------------------
>> Name: SDF5_May_deep.fits
>> SDF5_May_deep.fits Type: unspecified type (APPLICATION/octet-stream)
>> Encoding: BASE64
>
Mamoru Doi
Institute of Astronomy
School of Science
Univ. of Tokyo
voice +81-422-34-5084
fax. +81-422-34-5041
doi@ioa.s.u-tokyo.ac.jp
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