[vsnet-chat 4467] 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.

Here I introduce you the summary of my experiments on estimating the
coefficient 'k' ( = - b(v) in Henden's paper).

1. Removal of the stars at edge, or too bright stars

In my last experiment, stars at edge, or too bright stars were also
included. So first of all, I removed those stars. I changed the
brighter limit of magnitude down to 9.5 mag.

The results are in the following web page:

  http://vsnet.aerith.net/tmp/b-v-tycho1/index.html

But I cannot see evident difference from the old results.

2. Tycho-2

My last experiment was based on the Tycho-1 Catalogue. Next I tried to
estimate the coefficient 'k' using the Tycho-2 Catalogue.

The results only using the Tycho-2 stars whose error of VT and BT are
smaller than 0.2 mag are in the following web page:

  http://vsnet.aerith.net/tmp/b-v-tycho2/index.html

But I cannot see evident improvement from the results using the
Tycho-1 Catalogue.

Many stars whose B-V value is greater than 1 mag seem to have large
magnitude error, larger than 0.2 mag. Therefore, many stars with large
B-V value are rejected in this experiment. Then the range of x axis
became small, and it seemed to cause it difficult to calculate the
gradient.

And I think the graph has large scatter, as large as the graph using
the Tycho-1 Catalogue, despite of the limit of magnitude error.

3. Composite of data

It seems to difficult to estimate the coefficient 'k' from each image
because of the large scatter. So I composed all data in one night and
estimated the coefficient 'k' from the composed graph. 

The results are in the following web page:

  http://vsnet.aerith.net/tmp/b-v-tycho1/composite.html

This is based on the Tycho-1 Catalogue.

The linear function calculated in the method of least squares is
described for each night. There is a summary table at the end.

The graph impresses that the coefficients of the linear function are
large because of the large scatter. However, the calculated errors of
the coefficients are small.

However, the results are:

- The mean coefficient 'k' for KAF is -0.40, which does not coincide
  with the Henden's value.
- In one night, the 'k' for KAF became -0.2734, much different from
  other nights.
- There is no relation between the coefficient 'k' and the CCD chip
  and lens among the results of Torii-san's images.

4. Evaluation of Henden's value

Using the composite data, I estimated the error using the calculated
linear formula, and the error using the Henden's b(v) value. There is
the summary table at the end.

There is no evident difference between the error using the calculated
linear formula and the error using the Henden's b(v) value, even
ignoring the influence of lens, and even assuming that the Henden's
value fits to our systems.

5. Conclusion

- It is impossible to estimate the precise coefficient 'k' from the
  MISAO images whichever using Tycho-1 or Tycho-2, even if there are
  some hundreds of stars.

- In order to determine the 0-point of magnitude for our systems, we
  can use the Henden's b(v) value. We do not have to (should not)
  calculate the coefficient 'k' for our system every night.

- We do not have to consider the influence of lens to determine the
  0-point of magnitude for our systems.

- Comparing the imagae with lens and the image without lens, how much
  difference of magnitude is required to believe the star is a real
  variable star? We could not find the answer in this experiment.

Best regards,

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

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