This video is the fifth in a series on ImViz. In the previous video, we showed how to open and explore the plugin toolbar. In this video, we will demonstrate how to perform Aperture Photometry.
First we need to draw your apertures using the Region tool. We first zoom-in to better see the stars We draw a circular region subset around both a galaxy and a star. In the plugin toolbar we see our apertures represented in the subset tools.
Right now, we can see the subset region definitions. In the future, we will have more ability to manipulate the subset from this dropdown. Next, we open the aperture photometry plugin.
We select our aperture of interest as well as our background estimate. In this case, we will apply an Annulus with the parameters shown. There are other variables to enter if you know them, such as the pixel area, the DN per second conversion factor and the flux scaling to derive your magnitude.
For JWST these values will be automatically inserted once the values are known after commissioning. Next, select your plot type, we select the radial profile and then hit calculate. The fact that maximum pixel radius is offset from zero suggests that the aperture is not quite centered.
We can try again with a new subset better centered on the star Our new plot looks good. Below the plot we see all the photometry results for this new subset. Because we did not enter our values for DN per second and zero point magnitude those values are not filled in initially.
But upon entering the values we are able to populate those variables. Next, we want to extract the results back into our notebook. The ability to easily switch between the tool and the notebook highlights the power of ImViz.
In this case, we have two commands in our notebook. The first reads the Aperture Region Subsets into Astropy regions, which can be saved and used throughout the notebook if desired. The second command reads the photometry results back into the notebook as a table so we can scroll through or manipulate as desired.
This concludes our simple introductory videos to ImViz. There are many other exciting features and capabilities possible. Please be sure to click on the link to view our documentation and example Jupyter Notebooks that incorporate JDAViz and other JWST data analysis tools and methods.
Also, continue watching to view our other JDAViz videos demonstrating how to work with spectra, multi object spectra, and data cubes.
