Week 6: Astropy, Exposure Times, Standard Stars, and Graphs

Hello, everyone! Welcome back to my blog. In last week’s post, I detailed a series of challenges encountered while trying to correct star magnitudes using camera exposure times. I also made a mistake by incorrectly setting the aperture size for the software, which led to Source Extractor not recognizing some instances of my supernova. This necessitated a redo of the work.

I started this week off with an array of the exposure times for each file, sorted by date. I’ll use this data to finally correct my magnitudes.

Correcting the Magnitudes:

So far, if I chart my supernova’s raw magnitude over time, I get this graph:

https://ibb.co/s6g8tvP

The ideal graph is a neat, orderly line that slowly rises, hits a peak, then quickly drops down (i.e. an exponential decay curve). This is partially reflected by my curve — you can see how the peak values are relatively smooth, but quickly devolve into chaos as the magnitudes decrease.

After I correct using exposure times, I should get a smoother curve. This is what my graph looks like after the correction:

https://ibb.co/ggmD3f7

It looks a lot messier, but it has actually been corrected. The curve is more pronounced — here is a version with better illustration:

https://ibb.co/r30fbvj

You can see how now we can draw a line of best fit. All those values which seem really random will hopefully be corrected using standard stars, which is where I’ll extract the brightnesses of a nearby star from every image to use as a “standard”. This corrects for any inconsistencies between photographs (such as cloud cover, moisture, dust, etc.) 

I started by first identifying a standard star — I chose USNOA2 0450-17805518, which is right next to my supernova. I identified the star using Sky Map (I entered my galaxy into their system and found an identifiable star). Sky Map tells me that the apparent magnitude of that constant star is 14.35. 

However, I ran into another issue with extracting the magnitudes of this star in my images (some of my images are lined up improperly). I hope to resolve this over the weekend, and finish my corrections with my standard stars.

Thank you for reading my blog, and see you all next time!