Period uncertanties

American Association of Variable Star Observers (AAVSO)
Sun, 06/20/2021 - 12:25

Hello All, 


I am completing some data analysis on a variable star and have good results finding the period.

However, can I get a period uncertainty (+/- ...days) in V-Star?

Any help is greatly appreciated.

Thank you


Astronomical Society of South Australia (ASSAU)
Period Uncertainty

Hi John

That's not currently implemented in VStar. The DCDFT implementation is a port of Fortran code, which as far as I'm aware, does not provide this information either.

Other than drawing some conclusions based upon the resolution specified in the DCDFT parameters dialog or using the Current Mode ANOVA plugin (or use the AoV period search plugin and compare results with DCDFT), there is no intrinsic uncertainty information available.

A similar question has been raised in the past about polynomial fit in this forum. Right now, AIC, BIC, RMS and ANOVA can be applied for polyfit but again there's no intrinsic uncertainty information available. 

I would welcome input from you or others in AAVSO re: the best way(s) to implement uncertainty analysis this for DCDFT and polynomial fit. I don't claim to have particular expertise in that area but I'm willing to learn. Brad Walter, for example, may well have specific thoughts about this.


American Association of Variable Star Observers (AAVSO)
Thank you David

Thank you and apologies for the slow reply. i just realised I hadn't subscribed to this thread. 

I'll run the data through the different methods and see what I find.



American Association of Variable Star Observers (AAVSO)
VStar 2.22.0

The manual that you access from the help menu of 2.22.0 is the manual for 2.21.0 and doesn't have info about uncertainty estimates for the DCDFT Models. However, if youuse  the VStar online link in the help menu and click on the USER MANUAL bold heading and download the 10 mb manual using the download button on that github page you get the 2.22.0 manual which has info on the uncertainty estimates. Page 69 of the manual contains the following statement:

"In most cases the possible range estimated by the theoretical formula is too liberal while
the range estimated by FWHM is too conservative."

It is important to understand that "too liberal" means underestimates the error and "too conservative" means over estimates the error. By calculating both estimates one can get lower and upper bounds for the uncertainty. 

Brad Walter, WBY

American Association of Variable Star Observers (AAVSO)
VStar User Manual Updated

Hello Brad & David,

Thanks for pointing that out. I just updated the copy of the User Manual that is linked from VStar's "Help" menu item so it should be OK now.

Best wishes,