[vsnet-chat 4465] Re: MISAO color coefficients

[Seiichi Yoshida <comet@aerith.net>]

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

I am Seiichi Yoshida working on the MISAO Project.

Thank you so much for your comments.

Dr. Skiff wrote:
>      The second derives from the comment that the photometric reference was
> to Tycho (1 or 2?) stars fainter than mag. 8.5---but as faint as mag. 13,
> the implication is that the plots involve stars right to the catalogue limit.
> Bear in mind that fainter than about mag. 10.5 or so, the errors on the Tycho
> photometry increase rapidly, and are of a size to account _entirely_ for the
> scatter we see in the plots.

I used the Tycho-1 in the past, and now I used both the Tycho-1 and
Tycho-2 catalogues. But anyway, most of the stars are fainter than
10.5 mag. So maybe it is natural that the data have large scatter.

>      I would recommend omitting any Tycho star with errors of 0.05 or greater
> from the analysis (or perhaps > 0.03 if this leaves enough points to do the
> fit---two dozen stars with a good range in color is sufficient).  This will
> probably clean the plots up considerably, and make the fits to 'k' more
> consistent.  One should use Tycho-2 for this, because Tycho-1 contains a scale

I tried to reject all data whose magnitude error is larger than 0.08
mag. Then the number of data became small, many images contain 10 data
or less. And most of the data have small B-V value, and the range of x
axis became small. In addition, we can still see scatter on the graph
around several tenths of magnitude, although the standard deviation
must be much smaller.

As Dr. Henden wrote, I should take some images in good night of the
fields of Landolt stars, if my main purpose is to determine the system
formula. But my main purpose is that described in my last mail.

Most of the MISAO images do not contain the Landolt stars. They only
contain some Tycho stars. Some contain few Tycho stars. So we have to
determine the 0-point using the Tycho Catalogue at best, or GSC or so
in some bad cases. Even using the Henden's b(v) value, I think we can
determine the 0-point of magnitude for our systems with about 0.1 or
0.2 mag order of accuracy. 

So I give up to determine the accurate 'k' value for our images and to
conclude how the reflector/refractor difference or the use of reducer
lens influence to the b(v) value.

Best regards,

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

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