[Aavso-photometry] Mentoring for your 0.5 meter Cass

[Chuck Pullen]

Hi Derek - we've spoken before (email) re: IOTA occultations.

I live in Sacramento and am fairly adept at multi color photometry.   
I would be happy to help you out if I can.  Some initial suggestions,  
some of which you may have already done.

First off, get and read Henden and Kaitcheck "Astronomical  
Photometry" from Willman-Bell.  It's old, and based on single star  
photomultiplier tube detector technology, but everything in it is  
pertinent.  Be sure to pay at least $20 over the cover price of the  
book and tell WB to send the rest to Arne for his desert island  
retirement fund... :-)  (just kidding, Arne)

Second - download and read AAVSO's CCD Photometry Guide available  
from the AAVSO web site.  Note that Arne is in the process of  
updating this, but for now it is what there is.

Third - Try some of the Landolt (1992) fields   These are much less  
crowded than M67 and you'll get better results with out a steep  
learning curve.  Arne has a file of his preferred fields (of the  
hundreds in the Landolt publication) available in the AAVSO ftp  
site:  ftp.aavso.org/public/landolt.  Just download and print out the  
entire directory.  There are 13 fields in it with the photometry and  
finder charts.  Each chart and data matrix is a Postscript file but  
you should be able to print them with any Postscript printer or  
convert to PDF if needed.  I can convert and send you PDFs if you  
need them.

Forth - play!  Start with just V filter photometry on one Landolt  
field, using a comp star in the field for the rest of the Landolt  
stars in the field.  See how your C-K rms values change with  
airmass.  Then try going back and forth between two Landolt fields of  
different air mass.  Do this in multiple filters, and see how your  
results are effected by extinction and local weather effects (haze,  
clouds, moonlight, light pollution etc.)  Do all you initial work on  
stars that don't change brightness, so you will understand how to  
interpret data on stars that do change.  This is where you will  
really see the effects of poor darks, bias, and flats and be able to  
work up  a standard method specific to your equipment so that you can  
do everything the say way every time for maximum precision.

Try some single color work (V) on some fast RR Lyr, SX Phe, or EBs of  
reasonable brightness and short period.  I can suggest some stars, as  
can others.  The point of this is to get confidence in your technique  
and calculation methodology.  And it's fun. Be sure to send your  
results to AAVSO, every measurement is valuable.

Then, and only then, we can start using the Landolt fields to  
determine your transformation coefficients for multi color work.   
Once determined, with acceptable error, you can then test them on M67  
or better yet, new ( to you) Landolt fields to see how well they work  
and to get the hang of the techniques of multi color work.  Once you  
are comfortable there, then you can start to move to new fields once  
they have been calibrated.

Finally, you can work to learn how to calibrate unknown fields from  
Landolt standards fields, as Arne has made a career doing.  It's not  
hard to do, just hard to do right.  Many professionals don't do it  
correctly all the time.  Sometime that biases their work, other times  
it doesn't.  But it is something you can contribute to once you get  
good enough because there is always a need.

Hope this helps a bit.  Let me know off list if I can do more.

Quick questions:  Where is the scope, what kind of camera do you  
have, and what kind of photometric software were you planning on using?

Chuck

Chuck Pullen
pullenc at gmail.com