Is it possible to get the zeropoint of a deep coadd image?
I have generated image cutouts of a range of sources in all photometric bands (using SIA), but the zeropoints are not present in the FITS file header.
I have seen in the documentation that it is is possible to get the zeropoint of a single visit image using the CcdVisist table, but can’t find any information of whether this is available for a deep coadd image?
If you’ve loaded your deep coadd image into Python, you should be able to query the attached photometric calibration information for the zero point. E.g.:
zero_point = deep_coadd.photoCalib.instFluxToMagnitude(1)
Hi Lee, thanks for your help.
Is it possible to get the zero point information from SIA? This method only seems to work for the Butler service.
Thank you.
I think the photoCalib data from the butler is the best way to get the information you’re asking for.
Depending on what you’re trying to do, you may just be able to use the coadd image directly. If you’re trying to calculate magnitude, recall that our coadd outputs are recalibrated into units of nanoJansky. Following Equation 19 here, you should be able to convert from pixel flux to magnitude using:
m_AB = 31.4 − 2.5 log10(flux_nJy)