SIMBAD references

Stars on the asymptotic giant branch (AGB) show broad evidence of inhomogeneous atmospheres and circumstellar envelopes. These have been studied by a variety of methods on various angular scales. In this paper we explore the envelope of the well-studied carbon star TXPsc by the technique of spectro-astrometry. We explore the potential of this method for detecting asymmetries around AGB stars. We obtained CRIRES observations of several CO Δv=1 lines near 4.6µm and HCN lines near 3µm in 2010 and 2013. These were then searched for spectro-astrometric signatures. For the interpretation of the results, we used simple simulated observations. Several lines show significant photocentre shifts with a clear dependence on position angle. In all cases, tilde-shaped signatures are found where the positive and negative shifts (at PA 0°) are associated with blue and weaker red components of the lines. The shifts can be modelled with a bright blob 70mas to 210mas south of the star with a flux of several percent of the photospheric flux. We estimate a lower limit of the blob temperature of 1000K. The blob may be related to a mass ejection as found for AGB stars or red supergiants. We also consider the scenario of a companion object. Although there is clear spectro-astrometric evidence of a rather prominent structure near TX Psc, it does not seem to relate to the other evidence of asymmetries, so no definite explanation can be given. Our data thus underline the very complex structure of the environment of this star, but further observations that sample the angular scales out to a few hundred milli-arcseconds are needed to get a clearer picture.