A high-velocity transient outflow in η Carinae

We analyze velocity profiles of the X-ray spectral lines emitted by the h Carinae ( h Car) stellar binary at four epochs, just before the X-ray minimum ( associated with periastron) and more than 2 years before the minimum (similar to apastron). The profiles are nicely resolved by the HETGS spectrometer on board Chandra. Far from periastron, we find symmetrical lines that are more or less centered at zero velocity. Closer to periastron, the lines broaden, shift toward the blue, and become visibly asymmetric. While the quiescent X-ray emission and slight (< 200 km s(-1)) centroid shifts can be ascribed to the ordinary continuous binary wind interaction and to the orbital velocity of the secondary star, the observed high-velocity emission up to similar to 2000 km s(-1) and the abrupt flares during which it occurs cannot. This leads us to interpret the high-velocity flaring emission as due to a fast collimated outflow of ionized gas.