Assessing the Improvements GAIA-DR1 Will Bring to Dynamical Astronomy

Abstract: The first part of this thesis deals with the dynamical estimation of the Oort constants using proper motions and parallaxes provided from the Gaia-DR1 TGAS catalogue. The photometric information was provided by the 2MASS catalogue. The Oort constants calculated from the TGAS catalogue are compared to those obtained from the original Hipparcos catalogue in order to attempt to estimate how well Gaia-DR1 performs. A least squares approach was implemented to calculate the Oort constants. This routine contained seven parameters where the stellar LSR velocity components were included as well. The overall trend seems to be such that the TGAS catalogue can provide meaningful and potentially better results compared to that of the Hipparcos catalogue if the study is not sensitive to a catalogue that is colour incomplete. TGAS worked fairly well in the determination of the Oort constants mainly due to its large sample size, giving it a statistical edge over the Hipparcos catalogue. In the second part of the thesis the local mass density, ρ₀, was determined using tracer star populations for two catalogues. The first one was the original Hipparcos catalogue where the data was propagated to the year 2015. The second catalogue was a combination of Hipparcos stars obtained from both the TGAS and the propagated HIP catalogues. This was done in order to avoid the incompleteness issue that resulted after the creation of the TGAS catalogue. The estimated local mass density from the propagated Hipparcos catalogue was ρ₀ = 0.112 ± 0.009 solar masses per pc³ while the combined TGAS sample got ρ₀ = 0.113 ± 0.006 solar masses per pc³. This result implies that the TGAS catalogue is slightly better compared to the HIP catalogue in performance since it provides with lower formal errors. Based on the results of the two dynamical estimations performed, the TGAS catalogue can be seen as marginally better when compared to the HIP catalogue. In addition, the formal errors resulting from the calculations using the TGAS catalogue are better compared to those obtained using the HIP catalogue. The formal errors are especially good when dynamically estimating the Oort constants since so many stars are included in the calculations. It is, however, difficult to estimate the performance of the complete Gaia catalogue by simply considering the first data release. The release of Gaia-DR2 will hopefully resolve the questions surrounding the performance of the Gaia catalogue.