CY Aqr - Primus inter pares

tl;dr - The study of the variable star CY Aqr is a long-term and well-aged project of our astronomy group. Since 2008 a considerable commitment has been made and it payed off with the publication of several scientific papers. Time for a look back.

The star CY Aqr in the constellation of Aquarius is especially dear to our hearts. Our first tries at measuring the changing brightness of this remarkable variable date back to - from the viewpoint of current students - almost prehistoric ages, i.e. the year 2008. Now, more than 13 years later, it is time for an inventory. I figure it's not a spoiler at all if I anticipate to you: We were busy as bees.

season nights frames maxima
2008 14 5291 28
2010 12 2346 24
2011 12 3466 29
2012 5 1296 7
2013 7 2242 15
2014 6 3819 16
2015 21 9544 31
2016 10 5554 23
2017 6 2914 11
2018 7 4379 17
2019 4 2536 10
2020 5 2817 13
2021 7 3576 13

116 49780 237

The table above gives the number of nights we spent on the observation of CY Aqr, the number of image frames acquired in each season and the number of maxima derived from these data. The star has quite a short period of less than 90 minutes, so during one night we usually are able to witness 2-3 of its brightness peaks. 

A snapshot taken during one of the observations in 2021. You can see part of the light curve on the right screen in the background.

One of the 50000 image frames along with the light curve. Each dot represents an image frame and its corresponding brightness measurement.
The star CY Aqr is highlighted with a red arrow.

However, observing is only one part of the job. The best data is useless if you don't squeeze the scientific juice out of it. In the case of CY Aqr we are interested in the exact moments of maximum light, actually the (systematic?) deviation of these times from the prediction. That means we have to give a very close look at our light curves to nail down the location of the peak. 

Now wipe off that indulgent smirk from your face. The task is much less straightforward than you might think. Let me clue you in!

Exemplary close-up views of two of the maxima of CY Aqr. The circles are data points and the red line shows the moving average.

Give a look at the 'circle soup' above and point at the exact location of the maximum. Bear in mind that every data point represents a single exposure of 15 s, so the spacing in between them is 15 s, as well. Now of course we'd love to have a precision in the order of a few seconds only. Not exactly as easy as pie, is it?

In 2019 we decided to investigate the question, how good we actually were at this peak-peeking game.  Six students were summoned on January 17th and fed with data - loads of. It's plain as a pikestaff that there are more entertaining ways to spend an afternoon, however, when astronomy duties call ... 

Grin and bear it!

That's it! Now let the teacher type that into a spreadsheet.

Now it was my turn to do my stint. I added my own measurements and the one's of Prof. Christiaan Sterken - the secret mastermind behind all our efforts concerning CY Aqr - to the pile and entered them into a spreadsheet. Under the loving caresses of a linear fit with constant slope and subsequent calculation of the standard deviation of the residuals, the numbers slowly melted away to leave behind nothing more than the long sought quality estimators of our work.

Big surprise: The professional astronomer is best at what he does. Prof. Sterken achieved a standard deviation of only 14 seconds from the 'true' maximum. Hats off! After this no brainer, guess what, the teacher came second! 

Proud second.

I was able to limit my scatter to 18.35 seconds, however Maximilan (with 20.41 seconds) and Pauline (with 21.90 seconds) were hot on my heels. Luckily my two adversaries kindly left school one respectively two years ago 👋 - obviously to study physics 😍 - leaving behind some much appreciated breathing space for me. 😅

Christof Wiedemair



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