A study of the chromospherically active binaries UX Fornacis and AG Doradus

Abstract

This paper presents a time-series spectrum analysis of the two chromospherically active binary stars, UX Fornacis and AG Doradus. To investigate the rotational behaviour, in combination with activity in the Hα line, we obtained almost 40 high-resolution, high-S/N spectra for each system. Both binaries, UX For and AG Dor, show Hα of the primary star in absorption but filled in by chromospheric emission while the Hα line of the secondaries appear in pure emission. Line variations are seen and are approximately 5-sigma detections but are not linked to the orbital nor the rotational periods and seem to be erratic. We obtained new orbital elements for both systems and used them in combination with Hipparcos parallaxes and our Hα -spectrum synthesis to determine absolute parameters. We present the first Doppler image of the AG Dor primary using line-profile variations of the Fe i lambda 6546 line. The image reveals a cool polar feature and three equatorial spots with an average surface temperature difference, photosphere minus spots, of up to 1500 K for the polar spot and ~800 K for the equatorial spots. Since AG Dor is one of the slowest rotators (vsin i=18 km s^-1 ) that has ever been Doppler imaged, we present several tests to demonstrate the external consistency of our map. Based on observations obtained at the European Southern Observatory, La Silla, Chile.