[vsnet-chat 4441] Re: Apogee AP-7p

[Seiichi Yoshida <comet@aerith.net>]

Dear Dr. Skiff, Dr. Henden, and colleagues,

I am Seiichi Yoshida working on the MISAO Project.

Many thanks for your information, and very sorry to be so late to
reply you...

Dr. Henden wrote:
> The M67 paper does cover the AP-7, which lists
> a canonical "SITe back-illuminated CCD,"
> in this case the SI502AB.  The coefficients I

Thanks for your information. Masayuki Suzuki also told me that the
chip of Apogee AP-7p is SITe back-illuminated.

Dr. Skiff wrote:
>      You don't say what you did to determine the coefficient 'k'.  Why is
> there such a spread in the coefficients during a single night?  The plot
> one would like to see is one showing the difference of the instrumental
> magnitudes from the standard V (or R) as a function of B-V (or V-R) from
> a single night.  The slope of the data in this plot would be 'k'.  That
> there is some range of values implied for a single night in your figure
> means something is wrong either in the data or how you're determining
> the coefficient.

I wrote a simple web page to show the way of estimating the 'k'
value. Please see the page:

  http://vsnet.aerith.net/tmp/b-v/index.html

I have many many images, but each image contains only around 10 Tycho
stars in the field. I estimated the 'k' value for each image by
solving the following formula in the method of least squares.

    (Instrumental mag) - (Johnson V in the Tycho Catalogue) 
	= k * (B-V) + offset

    * Instrumental mag = - log_2.512 ( pixel count )

In the web page, I show you graphs of some images which shows the
difference of the instrumental magnitudes from the standard V as a
function of B-V, as pointed out by Dr. Skiff.

Actually, the Torii-san's images are about to be examined by the MISAO
Project. All of the past MISAO new variable stars were discovered from
the KenIchi Kadota and Nobuo Ohkura's images using the KAF chip. So I
also show the results of thier images.

The results of KenIchi Kadota and Nobuo Ohkura's images are similar in
every night. And the 'k' value is similar to the Henden's value for
KAF chip. But the results of Ken'ichi Torii's images are not. I do not
know why.

The plotted dots are scattering widely. And there are some wrong dots
in some graphs. I think it is one of the reasons why the 'k' value
from each image has large scatter even in one night. I did not exclude
the wrong dots to calculate the 'k' value. But I do not know why the
dots are scattering widely in every graph.

Dr. Henden wrote:
> so dramatically during a night.  I presume Seiichi's
> "k" is the same as my "b(v)".  I prefer to use a
> letter besides "k" since this is traditionally used
> for the extinction coefficient.

Sorry. I still use the letter 'k' in the web page. Please permit me
because the web page is temporary for vsnet-chat discussion. Well, my
'k' value has a opposite sign (plus and minus) against your
b(v), but can I replace the letter 'k' with 'b(v)' in my case?

Dr. Henden wrote:
>   As I mentioned in the paper, unfiltered measures
> are like extremely wide filters; very difficult to
> transform accurately into the standard system.  The
> traditional method of reporting unfiltered magnitudes
> has been CCD or CCD(C), but that doesn't adequately
> describe the results, since it depends highly on
> the comparison star magnitudes used in your differential
> photometry.  Were they V-band or R-band, or (groan) GSC?
> Did you attempt to transform onto the standard system,
> or just use the comp stars to zero-point your results?

I just use the comp stars to zero-point your results. I know it is
impossible to obtain the magnitude in standard system from unfiltered
CCD images using the transformation formula. 

I complete agree on you about the ambiguity of traditional style of
reporting unfiltered CCD images using letter 'C'. So in my own case, I
attach some additional information in comment columns when I report
the magnitude to VSNET. Actually I only attach the CCD chip name. But
now I wonder I should attach the lens name or "refractor" too when the
lens or refractor was used. Maybe we should attach the b(v) value too. 

Best regards,

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

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