[NOTES] DOLPHOT parameters
Instructions for DOLPHOT
- The ACS Nearby Galaxy Survey Treasury – The author of DOLPHOT (i.e. Andrew Dolphin) is a co-author here. In Section 6 is given an overview on how DOLPHOT works. Gives separate advices for the ACS and WFPC2 cameras.
- Sarah Bruzzese’s thesis – She exchanged several mails with Andrew Dolphin and reports several common mistakes/misinterpretations.
- The posts in my BLOG.
Rejecting fake detections in crowded fields
▸ The DOLPHOT ACS manual suggests using Force1 =1 (i.e., all objects are assumed to be of type 1 == stars) in case of crowded fields.
When using this options, the manual suggests to use the following output parameters to discriminate real sources:
- χ (PSF fit Chi) – This is not a reduced χ. The degrees of freedom are:
FitSky =< 2 ⇒ 1 degree of freedom (only the height of the PSF is fitted)
FitSky = 3 ⇒ 2 degrees of freedom (the sky is fit as well)
FitSky = 4 ⇒ 2 degrees of freedom (?not explained in the manual?)
.. so calculate the reduced χ accordingly.
- sharpness (sharpness = 0 ⇒ perfect PSF; -0.3 < sharpness < 0.3 ⇒ good star) .
▸ An other suggestion for crowded fields (see The ACS Nearby Galaxy Survey Treasury, Section 6, 8th paragraph) is to try FitSky = 2.