Hubble space telescope stis spectrum of RW Aurigae A.: evidence for an ionized beltlike structure and mass ejection in timescales of a few hours

Abstract

Profiles of the UV semiforbidden lines of C iii]1908 and Si iii]1892 of RW Aur have been obtained with the Hubble Space Telescope (HST) STIS. The C iii]1908 profile shows two high-velocity components at v = ± 170 km s-1 and a central one. The Si iii]1892 profile is very broad (FWHM = 293 km s_1), and the high-velocity components are unresolved. The high-velocity components are most probably produced in a rotating belt similar to that detected in other sources of bipolar outflows. A radius between 2.7 R* and the corotation radius (6.1 R*) is derived, and a log Te (K)≈4:7 and log ne (cm-3) = 11:6 are estimated. The belt is clumpy, and the most likely source of heating is local X-ray radiation, probably associated with the release of magnetic energy. In addition, profiles of the optical lines of He i, Fe ii, and H_ retrieved from the HST archive have been analyzed. The spectra were obtained by shifting the STIS slit between exposures in the transverse direction to the flow. Two features vary from one exposure to another: a blueshifted emission feature (detected in the Fe ii and He i lines) and a redshifted absorption feature (detected in H_), which are observed at the velocity of the blueshifted and redshifted components of the jet, respectively. There is a clear-cut correlation between the equivalent widths of these two components. These components are not associated with the flaring activity of the source, since they remain stable timescales of ’40 minutes. They are most likely associated with variations in the stellar/circumstellar environment in timescales of a few (’5) hours, consistent with reports by other authors for variations of the veiling and the appearance of shell signature in the optical spectrum.