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O-C "How-To"

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BGW's picture
O-C "How-To"

Attached here are the slides from my talk at the "How-To Hour" talk at the AAVSO General Meeting in Las Cruces today (October, 2019).

I've removed my email address from the document, but feel free to contact me by clicking on my observer code ("bgw") displayed next to this post, and using the "contact" facility. (You must be signed in with your AAVSO id for this.)

Gary Billings

B.P.Vietje's picture
O-C How-To

Thank You, Gary -- this is a topic I've wanted to learn more about.

Hope the meeting is going well!

Clear skies,

Brad Vietje, VBPA

Newbury, VT


Thanks for posting your talk.  One of the reasons I stopped going to AAVSO meetings is that the proceedings are not published.  Hopefully your example will provide an impetus to other speakers to make their slides available.

Ed Wiley_WEY
Ed Wiley_WEY's picture
O-C How To

Thanks Gary, I enjoyed the talk and our discussions at the meeting.


arx's picture
O-C How To

Great paper, Gary. A lot of work in that!

Near the end of the presentation, the slide on the infamous Polaris "glitch" contains the elements of the 2nd order polynomial expressions that describe the parabolic O-C curves before and after the glitch, and, for each O-C curve, the rate of change of the period, dP/dt, in units of sec/year.

If you are not familiar with this type of unit, it may not be immediately apparent how it is calculated. But it may be necessary to do so, since it and similar units are regularly used in professional publications on constant rates of change in variable stars.

A few year ago, I published a paper in JAAVSO which was a 'how to' for O-C diagrams for pulsating variable stars with linear and 2nd order polynomial ephemerides. In part, it has a step-by-step method to calculate dP/dt values.

It is attached, in case it is of any use to observers and potential authors.

Roy Axelsen


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