XY LMi - Primary minimum

[coatesg]

Last night I observed a minimum of the EW type star XY LMi, which is an EW type eclipsing binary with catalogue period 10.48535 h. 

The time of minimum appears to be -0.0542d different to the predicted minimum from the Lichtenknecker Database value - this star has a last observed minimum in that database on 11/03/2017 where the ToM was -0.0395d different to the predicted value - the O-C curve plotted with my own timing point seems to show that the curve in O-C (B-R here) appears to be carrying on in the same manner as before, but obviously with no intervening data!

 325 x 15sec exposures through a Astrodon V filter to get the following plot.

[andrew s]

Nice work. How did you determine the minimum?

Interestingly the O-C does not look linear so it might be more that a simple offset error.

Regards Andrew. 

[coatesg]

So I used the "Minima" software by Bob Nelson - available from https://www.variablestarssouth.org/software-by-bob-nelson/. 

It has several different ways of calculating the minimum - I think there's a little care in the usage here given the "flat bottom" to the minimum (esp when using Fourier methods), but it's reasonably straightforward to use - you just need to sense check the output (and the errors!)

Agree - the O-C looks like a curve - there will likely be mass transfer taking place here, and probably tidal changes, so there would need to be a lot more data over time to try and pin down exactly what it is doing. 

[Dave Smith]

Very nice. Well done Graeme.

Dave

[Whirlwind]

There's already a paper on this.  The changing period does appear to be known about.  Might be worth comparing.

https://iopscience.iop.org/article/10.1088/0004-6256/141/5/151

[coatesg]

17 minutes ago, Whirlwind said:

There's already a paper on this.  The changing period does appear to be known about.  Might be worth comparing.

https://iopscience.iop.org/article/10.1088/0004-6256/141/5/151

Oddly I've just been reading that very paper yes!  

[coatesg]

And yes - using their quadratic formula for the calculated minima, I get the O-C to be -0.00287d (-4m8s) for epoch 14980. Without going through the error calcs for the quadratic terms I'd be very surprised if this was outside of the error bounds!

[Dave Smith]

Here are the results of using Peranso.

 

Dave

[coatesg]

Well, that's pretty good - I got 2458911.4375 out of minima27 - estimated the error as +/- 0.0002. I think the polynomial struggles with the flat base to the eclipse (much like the Fourier fit). Doing the forwards/backwards graph would show a lack of overlap I think.

Thanks for putting the data through!

Edited March 5, 2020 by coatesg