Forum der Vereinigung der Sternfreunde

Hi togther!

Recently I had an interesting discussion about ProAm data policy with a lot of good ideas for future campaigns. We also discussed data reduction procedures for such campaigns, how to do it and if standard procedures are applicable for professional results. For that I recommend the very instructive paper Astronomical Spectroscopy of 82 pages by Phil Massey and Margret Hanson 2011 (http://spektroskopie.fg-vds.de/pdf/massey2010.pdf - already in the literature list of our website). A general but most important statement can be found in chapter 3. Observing and Reduction Techniques on page 31:

"The basic premise throughout this section is that one should neither observe nor reduce data by rote. Simply subtracting biases because all of one’s colleagues subtract biases is an inadequate reason for doing so. One needs to examine the particular data to see if doing so helps or harms. Similarly, unless one is prepared to do a little math, one might do more harm than good by flat-fielding. Software reduction packages, such as IRAF or ESO-MIDAS are extremely useful tools - in the right hands. But, one should never let the software provide a guide to reducing data. Rather, the astronomer should do the guiding. One should strive to understand the steps involved at the level that one could (in principle) reproduce the results with a hand calculator!"

I think this is not necessarily valid for pure amateur observations and the general desire to learn how to reduce data. However, if professional results are needed (and amateurs are able to contribute), this input from the professional side can guide us through future ProAm campaigns.

Cheers, Thomas

Hi Thomas:

I just wanted to echo your recommendation of the Phil Massey's paper/article; Phil is one of the best. I actually agree with Phil's assertion that you should be able to sit down with a calculator and determine, at least to first degree, the impact that each step in the reduction process has on your science data. An example: while it wasn't really an issue with the recent Mintaka campaign the common practice of subtracting a bias image, as opposed to fitting a very low order curve (perhaps fitting a plane) to the bias and then subtracting that from your science data, can be quite detrimental to the resulting S/N for faint objects. In particular I found his discussion of flats for spectroscopic data reductions very helpful.

Mike Potter
Baltimore, MD

While on the subject of flat fields, does anyone here have any experience of flat field correction for wide field slitless systems, particularly flat defects before the dispersing element (eg grism)

I am currently using this setup for a pro-am campaign on T Tauri stars
http://www.threehillsobservatory.co.uk/ ... tra_42.htm
taking flat fields with the grating in place which seems to be working ok but I am not sure if this is correct in general.

Thanks
Robin