Eclipsing behaviour of the radio emission in the Algol system V505 Sagittarii

We present radio interferometric observations of the EA2 Algol-type binary system V505 Sagittarii made with the ATNF Compact Array at 6 and 3.6 cm over one orbital cycle (1.18 d). We have obtained a strong detection of the source (1.5 mJy at 6 cm and 1.4 mJy at 3.6 cm) and derive a brightness temperature for the emitting region of Tb∼ 2.7 × 109 K, a magnetic field strength of 17 < B < 170 G and an electron density of Ne∼ 3.7 × 108 cm-3. The radio flux density levels show a clear modulation with evidence of eclipses of the emission region at both conjunctions of the binary. The form of the light curve implies that the radio source involves at least some enhanced emission in the intra-binary region. This has important consequences for the details of coronal formation and field interaction in active close binary stars. We discuss some scenarios for the formation of intra-binary active regions in Algol-type binary systems.