[Aavso-photometry] Differential transformation

[Chuck Pullen]

It's pretty crowded for me too!  I use a number of stars on the edges, and 
get about 12-15 usable ones in my 15 by 15 arc min field.  But at the heart 
of the "dipper" it's pretty hopeless.

For us IRAF users, the PHOTCAL task makes this all pretty easy.  If you 
shoot Landolt '95 fields at high and low airmass, then your unknown 
field(s), it calculates extinction and transformation and gives you 
corrected magnitudes for the unknown fields all in one shot.  The catalog 
is even in the software.  But, it is a bit of a black box, albeit a very 
well documented black box.  And you still have to be careful, as Landolt 
stars are not all equal in quality.

Chuck

At 10:19 12/29/04 -0600, Michael Koppelman wrote:

>For us wide-field guys M67 is pretty crowded. I have had good luck 
>observing Landolt fields. I made a database and imported it into TheSky so 
>I can easily see which fields are transiting.
>
>I wonder how you guys with small FOVs do it. I can get 5 to 15 Landolt 
>stars in a single field a lot of times. It would be painful to get only 2 
>or 3 stars in a given field.
>
>I do ignore extinction and just observe everything when it is at 45 
>degrees, which is where the Landolt fields are for me. This eliminates one 
>source of error but drastically restricts what I can observe when.
>
>Cheers,
>Michael Koppelman
>http://www.lolife.com/astronomy/
>
>
>
>On Dec 29, 2004, at 10:09 AM, Chuck Pullen wrote:
>
>>Gier - Note that M67 has been extensively studied and there are a number 
>>of stars available in it that should meet the quality test and Arne's concerns.
>
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