Short and long-term effects of GPS measured crustal deformation rates along the South-Central Andes

In this study we present the contemporary crustal deformation field along the central and southern Andes (17-42\deg S) estimated from four Global Positioning System (GPS) campaigns conducted in 1994-97. We find that the majority of the observed crustal deformation field is relatively homogenous: roughly parallel to the plate convergence direction with decreasing velocities away from the trench. We attribute this type of deformation pattern to the inter-seismic phase of an earthquake deformation cycle caused by 100\% locking of the thrust interface between the subducting Nazca and the overriding South American plates. We have also detected a strong post-seismic deformation signal in the vicinity of the 1995 M$_w$8.0 Antofagasta (22-26\deg S) and 1960 M$_w$9.5 Chile (38-43\deg S) earthquakes. This type of deformation can be described as short-term in nature compared to geological timescales. The above conclusions are based on the results of the 3-D Andean Elastic Dislocation Model (AEDM). By subtracting the AEDM predicted deformation rates from the observations we obtained a residual velocity field, that highlights the post-seismic, as well as more long-term deformation effects. For example, we find a strong evidence for the continuing crustal shortening across the back-arc, reaching its maximum (4 mm/yr) in the very north of our study area. In addition, between latitudes 29-34\deg S, there is an indication of E-W oriented extension within the fore-arc, in accordance with the recent geologic findings for the N-S oriented normal faulting

The complex environment of the bright carbon star TX Psc as probed by spectro-astrometry

Context: 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 TX Psc by the technique of spectro-astrometry. Aims: We explore the potential of this method for detecting asymmetries around AGB stars. Methods:We obtained CRIRES observations of several CO $\Delta$v=1 lines near 4.6 $\mu$m and HCN lines near 3 $\mu$m in 2010 and 2013. These were then searched for spectro-astrometric signatures. For the interpretation of the results, we used simple simulated observations. Results: 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 0deg) are associated with blue and weaker red components of the lines. The shifts can be modelled with a bright blob 70 mas to 210 mas south of the star with a flux of several percent of the photospheric flux. We estimate a lower limit of the blob temperature of 1000 K. 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. Conclusions: 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