Avståndsbestämning till AGB-stjärnor genom parallaxmätning

Sammanfattning

In this thesis distance to nearby AGB-stars – stars in the end of their lifecycle with amass of 0.8–8.0M⊙ – were calculated using parallax. The characteristical dynamic ofthese stars creates intensity fluctuations which together with their giant size makesmeasuring the coordinates of the stars a non trivial task. Different methods forestimating the centre point of the stars were evaluated. To obtain a good resolutionof the stars that were examined – R Doradus, R Leonis, W Hydrae, Mira A andB – several observations, separated in time, from the ALMA-telescope were used.Estimates for the parallax and proper motion – the stars apparent movement onthe celestial sphere, excluding parallax – were extracted by fitting the stars celestialmovement for the different methods. To achieve a better precision the resamplingmethod jackknife were used. The methods that gave the best result were gaussian fitand different variants of half max intensity fit. The gaussian fit gave the distances:47 +4−3 pc for R Doradus, 134 +71−35 pc for R Leonis, 106 +29−19 pc for W Hydrae, 121 +34−23pc for Mira A and 126 +55−31 pc for Mira B. The calculated astrometric values agreeswith values from the space telescopes Hipparcos and Gaia, however, the calculatedvalues for the proper motion have a better precision in comparison. Further studiesof the binary star Mira should take its orbit into account.