Minima of Eclipsing Variable Stars 

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Presentation of Eclipsing Variable Stars 

Eclipsing variable stars are binary systems in which two stars orbit each other. When one of the stars passes in front of the other from our terrestrial point of view, it partially or completely blocks the light of its companion. This phenomenon causes a periodic variation in brightness, observable in the form of eclipses. 

Primary and Secondary Minima 

These variations are represented by light curves that show dips called minima:

• Primary minimum: occurs when the brighter star is eclipsed by the fainter one. This is the deepest dip.

• Secondary minimum: occurs when the fainter star is eclipsed. The dip is shallower.

These minima are essential time markers for analyzing the orbital behavior of the system.

O–C Analysis and the LITE Effect 

Precise observations of the minima make it possible to calculate the O–C values (Observed minus Calculated), which represent the difference between:

• O: the observed time of the minimum (measured by photometry)

• C: the time calculated from a theoretical ephemeris

The analysis of O–C values is a fundamental tool for:

• Detecting period variations (accelerations, slowdowns, cycles)

• Revealing the presence of a third body (star or exoplanet) through the LITE effect (Light-Time Effect)

What is LITE? 

The Light-Time Effect (LITE) refers to the apparent shift in the timing of minima caused by the presence of an additional body in the system. This third body causes the binary system to move around a common center of mass, which slightly alters the distance between the system and Earth over time. As a result, the light takes more or less time to reach us, leading to periodic shifts in the observed minima.

This phenomenon is detectable in O–C diagrams and provides an indirect but powerful method for discovering invisible companions, such as exoplanets or faint stars.

Personal Contribution 

Since 2010, Maurice Audejean has been conducting these observations in collaboration with the Czech Astronomical Society, as part of the VarAstro-CZ program. This rigorous work by the astronomical society has made it possible to collect hundreds of minima of eclipsing stars and exoplanet transits, contributing to the enrichment of international databases. 

This page presents the observations recorded since 2025. Earlier observations can be found on the  Observations pour VarAstro CZ.