Affiliation
American Association of Variable Star Observers (AAVSO)
Sun, 11/06/2022 - 03:46
Would you kindly explain, what does "mid" mean in ephemerides? I tried to compare some mid dates with light curves, but did not understand :(
Dear Mikhail,
I assume you are referring to the VSX ephemeris.
Mid is the epoch of maximum for pulsating variables or the epoch of minimum for eclipsing binaries, RV Tau variables and dark-spotted stars.
"Mid" is used because for eclipsing binaries that have an eclipse duration value added, you also have Start and End. They are the beginning of the eclipse and the end of the eclipse respectively.
Cheers,
Sebastian
Thank you for your kind explanation!
Indeed, I'been discouraged by "mid" unexpected jump from EA minimum to pulsators maximum :) Moreover, I did not find obvious correlation between mid dates and miras light curves. Explain please why minima date is not used for all cases?
Actually, if you don't find some mira ephemeris to be correct, it is because the periods need to be adjusted or due to the period jitter some miras undergo. You would need to research each star individually in order to see what is happening. Maybe a VSX revision is worth.
Selecting epochs of minima or maxima is a convention, but it is mostly based on the fact that in eclipsing binaries minima are much sharper than maxima, and thus easy to measure, while in pulsating variables, it is usually the opposite: minima are shallower. You try to select epochs based on how accurate they can be, and the light curve shape plays a role.
Cheers,
Sebastian
Thank you again for clear explanation!
Perhaps, small "? - get description" icon within ephemerides table will not be redundant?