We present three transit observations of HD 189733 b obtained with the high-resolution spectrograph CARMENES at Calar Alto .
A strong absorption signal is detected in the near-infrared He i triplet at 10830 Å in all three transits .
During mid-transit , the mean absorption level is 0.88 \pm 0.04 % measured in a \pm 10 km s ^ { -1 } range at a net blueshift of -3.5 \pm 0.4 km s ^ { -1 } ( 10829.84–10830.57 Å ) .
The absorption signal exhibits radial velocities of +6.5 \pm 3.1 km s ^ { -1 } and -12.6 \pm 1.0 km s ^ { -1 } during ingress and egress , respectively ; all radial velocities are measured in the planetary rest frame .
We show that stellar activity related pseudo-signals interfere with the planetary atmospheric absorption signal .
They could contribute as much as 80 % of the observed signal and might also affect the observed radial velocity signature , but pseudo-signals are very unlikely to explain the entire signal .
The observed line ratio between the two unresolved and the third line of the He i triplet is 2.8 \pm 0.2 , which strongly deviates from the value expected for an optically thin atmospheres .
When interpreted in terms of absorption in the planetary atmosphere , this favors a compact helium atmosphere with an extent of only 0.2 planetary radii and a substantial column density on the order of 4 \times 10 ^ { 12 } cm ^ { -2 } .
The observed radial velocities can be understood either in terms of atmospheric circulation with equatorial superrotation or as a sign of an asymmetric atmospheric component of evaporating material .
We detect no clear signature of ongoing evaporation , like pre- or post-transit absorption , which could indicate material beyond the planetary Roche lobe , or radial velocities in excess of the escape velocity .
These findings do not contradict planetary evaporation , but only show that the detected helium absorption in HD 189733 b does not trace the atmospheric layers that show pronounced escape signatures .