[NOTES] DOLPHOT parameters

Instructions for DOLPHOT

DOLPHOT manuals are far from being complete, and the software (and its usage) sometimes is a sort of “black-box”.

Though, the informations contained in the following documents can be helpful:

•  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.

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