Class #15
Measure PSF and total magnitude
Create a coordinate system for the image

Measure PSF and total magnitude


• Choose a star on one of your reduced images, and measure its PSF with imexam-r.


• Does the fit look alright? Was the fit profile set to "Moffat" or "Gaussian"? Change this setting (→ epar rimexam) and repeat the fit. Is the difference negligible?

From the measured width and peak intensity, calculate the total magnitude (i.e. integrated to infinity) for both Moffat and Gaussian profile. How big is the difference?

Here is a possible solution, psffit.cl



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Creating a coordinate system for the image:


• Select several stars on your image, and obtain their exact center positions with imexam-a.


• Now obtain the accurate RA/DEC coordinates of them through the SDSS "image list tool". At this webpage, enter the coordinate of the galaxy (galAz = VCC490 at RA=185.411537, DEC=15.745108 — note that the FITS header says VCC308, which is wrong!).


• Write x,y,RA,DEC into an ASCII table and feed it into the task 'ccmap', together with your image (→ See the lecture).


Here is a possible solution, coordsys.cl