The O'Connell effect is an asymmetry in the photometric light curve of certain close

eclipsing binary star A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...

s. It was named after the astronomer

Daniel Joseph Kelly O'Connell Daniel Joseph Kelly O'Connell was a seismologist, astronomer and Jesuit priest who is particularly known for his work in observational astronomy. He worked primarily observing Binary star system, binary star systems, and was involved in photograp ...

, SJ of Riverview College in

New South Wales ) , nickname = , image_map = New South Wales in Australia.svg , map_caption = Location of New South Wales in AustraliaCoordinates: , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , es ...

who in 1951 studied this phenomenon and distinguished it from the so-called periastron effect described by earlier authors, as it does not necessarily appear near the

periastron An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any ellip ...

, when tidal effects and an increase in mutual radiation may cause an increase in

luminosity Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...

The effect

The out-of-eclipse brightness maxima of some binary stars are unequally high. This is contrary to expectations that the observed

of an eclipsing binary should be the same when its components switch positions every half period. The maximum following the primary minimum is nearly always brighter than the preceding one. This is called the positive O'Connell effect, the reverse case is referred to as the negative O'Connell effect. The difference increases with the ellipticity of the stars, and the differences in their sizes and

densities Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek language, Greek letter Rho (letter), rho), although the Latin letter ''D'' ca ...

. Also,

spectral ''Spectral'' is a 2016 3D military science fiction, supernatural horror fantasy and action-adventure thriller war film directed by Nic Mathieu. Written by himself, Ian Fried, and George Nolfi from a story by Fried and Mathieu. The film stars J ...

differences have been observed between subsequent maxima.

Attempts at explanation

In some systems where the phenomenon has been observed, such as in CG Cygni, RT Lacertae, XY Ursae Majoris, or YY Eridani, the luminosity difference between subsequent maxima has been found to be variable, in others relatively stable. Furthermore, it has been observed in a variety of configurations, such as over-contact, semi-detached, and near contact systems alike. These factors make an explanation difficult and suggest that various mechanisms may be responsible for the effect to manifest. Several reasons have thus been proposed: an asymmetric distribution of starspots, impacts of one-way gas streams between the components of the binary system, or the flow of circumstellar matter, asymmetrically deflected due to

Coriolis force In physics, the Coriolis force is an inertial or fictitious force that acts on objects in motion within a frame of reference that rotates with respect to an inertial frame. In a reference frame with clockwise rotation, the force acts to the ...

Examples

The O'Connell effect has been observed, among others, in the binary systems W Crucis, RT Lacertae, CX Canis Majoris, TU Crucis, AQ Monocerotis, DQ Velorum, and CG Cygni.

References

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External links

A Possible Explanation of the O’Connell Effect in Close Binary Stars
- Unsolved problems in astronomy Periodic phenomena Optical phenomena