X-ray accretion signatures in the close CTTS binary V4046 Sagittarii

Abstract

We present Chandra HETGS observations of the classical T Tauri star (CTTS) <ns0:ext-link ext-link-type="aoi">V4046 Sgr</ns0:ext-link>. The He-like triplets of $\ion{O}{vii}$, $\ion{Ne}{ix}$, and $\ion{Si}{xiii}$ are clearly detected. Similar to the CTTS <ns0:ext-link ext-link-type="aoi">TW Hya</ns0:ext-link> and <ns0:ext-link ext-link-type="aoi">BP Tau</ns0:ext-link>, the forbidden lines of $\ion{O}{vii}$ and $\ion{Ne}{ix}$ are weak compared to the intercombination line, indicating high plasma densities in the X-ray emitting regions. The $\ion{Si}{xiii}$ triplet, however, is within the low-density limit, in agreement with the predictions of the accretion funnel infall model with an additional stellar corona. <ns0:ext-link ext-link-type="aoi">V4046 Sgr</ns0:ext-link> is the first close binary exhibiting these features. Together with previous high-resolution X-ray data on <ns0:ext-link ext-link-type="aoi">TW Hya</ns0:ext-link> and <ns0:ext-link ext-link-type="aoi">BP Tau</ns0:ext-link>, and in contrast to <ns0:ext-link ext-link-type="aoi">T Tau</ns0:ext-link>, now three out of four CTTS show evidence of accretion funnels.