Otherwise the detection rate of binary cTTS would be much higher than the expected value, and for wTTS binaries it would be much lower. The detection bias concerning binary TTS in EO observations is . In this part of the analysis we have taken benefit from the fact that binary stars represent co-eval pairs which have evolved under the same conditions, and thus are represented by the same distance and metallicity. Furthermore, the detection of both components of wider pairs in X-rays is an indication that both stars are young, and therefore have evolved under similar conditions at the same time. In particular we have compared the X-ray emission of primary and secondary in resolved binaries to unveal influences of bolometric luminosity and rotation.
Primaries are more X-ray luminous than secondaries.
However, the faster rotating component always emits more X-rays than the slower rotating component. To distinguish between these two possibilities one should look for binaries where the secondary is the faster rotating component. We find that the faster rotating star always emits harder X-rays. This interpretation is supported by variability found in two primaries but in none of the secondaries. This research of made use of the Simbad data base, operated at CDS, Strasbourg, France.