Eclipsing Binary or Transiting Planet?
-
by
mlalkaka
What's the best indicator that this is an eclipsing binary star system and not a transiting planet?
Posted
-
by
davidbundy77
Take a look at the vertical scale. The brightness drops from about 1.03 to 0.64, that is a drop of about 39%. In order to cause such a huge drop the eclipsing object must be quite large compared with the star and couldn't possibly be a planet.
With some simple maths it is possible to compute roughly how big the drop could be and still be a planet. Ignoring various complications such as grazing transits, blending etc. the depth of the transit/eclipse is approximately equal to the square of the ratio of the radius of the eclipsing object and the radius of the star.
Suppose the star has the same radius as the sun. This radius is about five times the radius of the largest known exoplanets (about two Jupiter radii). The square of the ratio of the radii of a planet and the star is therefore at most (1/5)^2 = 0.04. So a transit depth of more than 4% is very likely to be an eclipse by a companion star and not a planet.
If the star is a dwarf then the ratio of the radii could be larger and still be a planet. So for a dwarf star the transit depths of a planet could be bigger. Here is a simple calculator by Planet Hunter Kian Jek for estimating the size of a transiting planet http://www.kianjin.com/pcalc.html
Posted