How to analyze occultations!

We have had our first “analysis party”- and it was a blast! Analysis is the final leap towards a positive report, in which we use computer programming to find the disappearance and reappearance of the star’s light as the asteroid passes over. Here, my friends, is your go-to guide to analyzing occultations for when the going gets tough (which it often does). If you have any questions or errors, reach out to me!

Access Pymovie via Python. The code lines read as follows: python, from pymovie import main, main.main() . Then, upload the fits files for the event.

Click the box that says “show image contrast control”.

You should now have at least three apertures marked on your screen.

Create a finder via fourier align. Make sure to run it for at least 100 frames, and that you redact 7 lines off the top of the files to erase the noise.

Then, head over to the tab titled “WCS”. You will need to create an account on Astrometry.net in order to use the program Astrometry.

Find the UCAC number for the target star of the event.

Put in the UCAC number where the program asks. Before you run it, make sure you redact 7 lines off the top of the images so that the program isn’t affected by noise. Click “Query Vizier”, and then once the program finds the coordinates of the target star, click “set as target”. The program will fail at first, once it does, click the button that says “astrometry WCS calib” and run the program.

Once Astrometry has defined the target star, and placed an aperture over it, we will need to place apertures over two other reference stars. Choose stars that aren’t too bright and aren’t too close to the edge of the screen. Right click on the first star, and select a dynamic aperture.

A dynamic aperture will track the star as it moves – we track the target star and one reference star in case the telescope moved during the recording. Make sure that when you name the aperture, it says “track”, so that the program tracks the star.

Repeat the process for the second reference star, except use a static aperture, which will move alongside the tracking apertures. It’s important you have at least two reference stars, and if the footage is bad, you may want to do more than two. Reference stars help us identify whether a dip in starlight is actually true, and not due to noise.

Keep the name simple for static apertures (or don’t, I don’t care). There is no need to put “track” since we aren’t using a dynamic aperture.

You should now have at least three apertures marked on your screen.

Now, let the analysis commence (aka – have a computer do it for us). Click the “analyze” button and cross your fingers.

Once all the frames have undergone analysis, click the plot button (I warn you, this is where many of the disappointments lie).

Search for the event. If there is no clear dip in starlight, refer to the predicted time of the event, and search for those files that pertain to the predicted time. If there is still no dip in starlight, the event was likely a miss (sorry).