Starspot - Detection and Measurements

Detection and Measurements

To detect and measure the extent of starspots one uses several types of methods.

• For rapidly rotating stars – Doppler imaging and Zeeman-Doppler imaging.

With the Zeeman-Doppler imaging technique the direction of the magnetic field on stars can be determined since spectral lines are split according to the Zeeman effect, revealing the direction and magnitude of the field.

• For slowly rotating stars – Line Depth Ratio (LDR).

Here one measures two different spectral lines, one sensitive to temperature and one which is not. Since starspots have a lower temperature than their surroundings the temperature-sensitive line changes its depth. From the difference between these two lines the temperature and size of the spot can be calculated, with a temperature accuracy of 10K.

• For eclipsing binary stars – Eclipse mapping produces images and maps of spots on both stars.