Post by Hosein on Jul 25, 2017 17:32:07 GMT 8
PSF is needed in order to have a robust fit essentially at the centre of a galaxy where the light gradient is steepest. You can estimate the PSF using ProFit itself by fitting the bright stars in the target field (well covered in the RPubs' vignettes) or the PSF might be already provided by a point spread function modelling tool, such as read_PSF tool for SDSS or TinyTim (Krist & Hook 2011) for HST.
For those of you who will be using ProFit on HST data the TinyTim manual is essential.
Whether using the web based TinyTim or the stand-alone version you need to provide bellow info as the input:
- The specific camera on HST which you wish to generate the PSF for (eg. NICMOS, ACS, WFPC, etc.).
- Chip: Specific detector of interest. You would be asked to select the 1st or 2nd cheeps on ACS, for example.
- Pixel Position: Since the PSF is field-dependent, the position on detector (x & y). A list of positions is accepted as long as they are saved in a file named as '@xy.lis'.
- Filter: Filter passband (eg. f475w)
PSF is filter dependent. Only applicable filters are given in the menu.
- Spectrum Type / Spectrum Value: Form of object spectrum should be selected here. eg. Blackbody, Pawer law, etc.
- PSF diameter: The diameter of the PSF. The recommended size is ~3 asec, however the maximum computable size is 30 asec.
Please note that the larger the PSF, the slower the fit as the convolution will take longer.
- Focus: The wavefront error due to secondary mirror de-space in HST could be optionally provided here in units of micron.
A model based on the measurements is available for any period of interest is available here.
The zero value will result into a PSF with no wavefront error in focus.
* Eventually, your PSF should look like this:
For those of you who will be using ProFit on HST data the TinyTim manual is essential.
Whether using the web based TinyTim or the stand-alone version you need to provide bellow info as the input:
- The specific camera on HST which you wish to generate the PSF for (eg. NICMOS, ACS, WFPC, etc.).
- Chip: Specific detector of interest. You would be asked to select the 1st or 2nd cheeps on ACS, for example.
- Pixel Position: Since the PSF is field-dependent, the position on detector (x & y). A list of positions is accepted as long as they are saved in a file named as '@xy.lis'.
- Filter: Filter passband (eg. f475w)
PSF is filter dependent. Only applicable filters are given in the menu.
- Spectrum Type / Spectrum Value: Form of object spectrum should be selected here. eg. Blackbody, Pawer law, etc.
- PSF diameter: The diameter of the PSF. The recommended size is ~3 asec, however the maximum computable size is 30 asec.
Please note that the larger the PSF, the slower the fit as the convolution will take longer.
- Focus: The wavefront error due to secondary mirror de-space in HST could be optionally provided here in units of micron.
A model based on the measurements is available for any period of interest is available here.
The zero value will result into a PSF with no wavefront error in focus.
* Eventually, your PSF should look like this:
