Re: Best way to do 400+ stars on three images

Posted by karenacollins on Dec 23, 2016; 8:05am
URL: http://astroimagej.170.s1.nabble.com/Best-way-to-do-400-stars-on-three-images-tp48p575.html

There is a trick to produce a Hertzsprung-Russell diagram (H-R diagram) completely within AIJ. You first need exposures of a cluster in two different filters. It has been a while since I actually produced an H-R diagram in AIJ, but here is a sketch of how to do it. First, run multi-aperture photometry on the two images as usual. Then select Multi-Plot Main->Table->Transpose Table. Next remove all of the resulting rows that are not Source-Sky_Xnn values. Using the Multi-plot_Y-data "Function", "Y-data", and "Y-operand" setting, create the Filter A - Filter B color and plot that vs. one of the filter source counts. I could be forgetting an important step, but that should give you the general idea. If need have more detailed question, let me know.

Regarding your "If not:" question: Multi-aperture records all aperture measurements in the table, but they are all recorded on one line (generally most sensible format for time series photometry). The above "Transpose Table" instruction inverts the table so that each aperture measurement is on a separate row so that the flux of all stars can be plotted.

Regarding your last question: You can provide a list of RA/Dec coordinates for all of the stars you want to measure. To see the required input format, define 3-4 apertures in a plate-solved image with WCS coordinates using multi-aperture, and press enter to perform the photometry. Those results are not important, but that last steps records the apertures in AIJ memory. Then go to Image_Display->File->"Export Apertures to RA/Dec list..." to create an example file. You can duplicate this file with one line for each star you want to measure. Then load the file using the Image_Display->File->"Import Apertures From RA/Dec list...". Now start multi-aperture and make sure "Use previous 'N' apertures" and "Use RA/Dec to locate apertures" is enabled. Press "Place Apertures" and then <enter> to start the photometric measurements.

Here is an example of what the RA/Dec input file should look like:
-------------------------------------------------------------

#RA in decimal or sexagesimal HOURS
#Dec in decimal or sexagesimal DEGREES
#Ref Star=0,1,missing (0=target star, 1=ref star, missing->first ap=target, others=ref)
#Centroid=0,1,missing (0=do not centroid, 1=centroid, missing=centroid)
#Apparent Magnitude or missing (value = apparent magnitude, or value > 99 or missing = no mag info)
#Add one comma separated line per aperture in the following format:
#RA, Dec, Ref Star, Centroid, Magnitude
06:30:31.870, +29:42:27.34, 1, 1, 99.999
06:30:32.781, +29:40:20.38, 0, 1, 99.999
06:30:22.613, +29:44:42.19, 0, 1, 99.999
06:30:00.055, +29:46:06.79, 0, 1, 99.999
06:29:48.332, +29:38:14.22, 0, 1, 99.999

Karen