Combining Hipparcos and Gaia data: Improved Astrometric Calculations With Orvara

Abstract: Hipparcos and Gaia are two missions intended to catalogue positions and motions of stellar objects. Orvara is a computer program which aims to combine the data from these two missions to calculate Keplerian parameters for stellar systems. In practice, Orvara can use any combination of radial velocity, relative astrometry and Hipparcos-Gaia data to generate results. I present an investigation of Orvara’s approach to calculate these parameters as well as orbital parameters for AF Leporis b, Smethells 119 B, Gliese 105 C and Gliese 86 B. The results were produced using Orvara and radial velocity data and relative astrometry data gathered from a variety of sources. The results in this thesis show the following: The exoplanet AF Leporis b was confirmed to exist with similar attributes as in other articles and the red dwarf companion Gliese 105 C was also confirmed to exist but with attributes that differ to some degree when compared to articles. For the two binary star systems, Gliese 86 and Smethells 119, the resulting parameters were quite different to those presented in other articles. The investigation of Orvara is conducted by observing how the posterior parameters change when data is removed or changed. It turns out that Orvara calculates accurate results when it is given all data that it can be given. From the results of this thesis one can conclude that there is a super Jupiter planet around AF Leporis, there is a red dwarf as the tertiary star in Gliese 105 and finally that Gliese 86 and Smethells 119 are binary systems of mass ratios 0.58 and 0.227. One can also conclude that Orvara only generates accurate results if all sets of data are given.