| | 7 | |
| | 8 | I've been largely focused on generating a clean reference photometry and astrometry database for MD04. Progress was slow because I spent most of the time discovering and fixing low-level bugs with the dvo database manipulation tools (dvomerge and photdbc, the latter of which had not yet been used very much). This was a good exercise, however, as if gives a good demonstration set to prove that all of these steps and tools are working. Here are the steps I followed (I am putting the actual commands on the wiki): |
| | 9 | |
| | 10 | First, I generated a griz database for MD04 from the Demo Month smf files for which the data was magicked. I discovered that we have not magicked (nor distributed) any of the y-band data for MD04. This is because there is no reference stack in y-band. I used some of the y-band smf files to generate a separate y-band dvo database. I ran relphot and relastro on both with several iterations to calculate good internal magnitudes and positions. I then used photdbc to extract a high-quality database for both the griz and y versions: this tool makes a copy of a dvo database, potentially restricting the data used in the copy. In this case, I limited reference database to the objects with more than 40 detections in griz (and 10 in y) and at least one of the average magnitudes needed to have an error < 0.025 mags. I then used dvomerge to combine these two reference databases. |
| | 11 | |
| | 12 | To tie down the zero point, I made a copy of this merged database and used addstar to incorporate some of the SDSS data from this field. I then extracted the photometry in the internal average PS1 system matched to the corresponding SDSS photometry and determined zero points. I reset the master databases to use these SDSS-tied zero points and regenerated the high-quality reference database. Note that for y-band, the zero point is crude: it is based on setting stars with i-z = 0.0 to have z-y = 0.0 (after i and z were corrected into the SDSS system). I did NOT apply any color terms at this point to determine the SDSS transformation, which means the zero points are only set for the mean stellar color. |
| | 13 | |
| | 14 | Finally, I merged the data for a wide region around MD04 from synthetic grizy database into this high-quality reference, using the magnitudes and positions of PS1 measurements where an object was present in the high-quality database, but accepting the synthetic data if no object was present. This last step allows us to perform astrometry with this database even on the images (and parts of images) that stick out beyond the main portion of the MD04 region. This reference database is now installed on the cluster, and I have begun the processing of the MD04 images using this new database as a reference. |
