[vsnet-chat 2171] Re: Supernovae estimates using USNO SA2.0

[Taichi Kato <tkato>]

Re: [vsnet-chat 2169] Re: Supernovae estimates using USNO SA2.0

Dr. Henden wrote:

>   Say that you have a sequence of reference (photographic) magnitudes
> as well as the instrumental counts/magnitudes from your CCD system.
> You can fit your data like
>    Mref = a + b * Mccd
>         = a + b * (-2.5 log (counts))
>         = a + k * log(counts)
> 
> where you might use a different k-value depending on the magnitude range
> you are trying to fit.
> 
>   This is a perfectly adequate way of transforming raw data into a reference
> system.  In fact, you use a similar technique when transforming your
> instrumental CCD data into the Johnson-Cousins system with Landolt
> standards as your reference.

    The reasoning of the equation is what Arne has explained.  But I don't
think it adequate to use it in system transformations.  I presume what
Arne has intended is actually

   Mref = a + Mccd + b * (color index)

   or something like this, and not

   Mref = a + b * Mccd

   Have I confused something?

Regards,
Taichi Kato

VSNET Home Page

Return to Daisaku Nogami

---

vsnet-adm@kusastro.kyoto-u.ac.jp