Filtyp
We test a new approach to calculate the mean velocity and velocity dispersion for a sample of nearby stars when their radial velocities are not available. The most commonly used method (here called the projection method, PM) was introduced in a paper by Dehnen & Binney (1998). That method is here compared, theoretically and numerically, with an application of the Maximum Likelihood (ML) method
Most of the things that we know about stars come from their spectrum. The properties of the atomic lines, e.g. energy levels, wavelengths, oscillator strengths, must be known to understand the observed spectrum and to perform quantitative analyses. Atomic data of some elements are incomplete, especially in the near-infrared region, which makes it difficult or even impossible to analyze a stellar s
Context. The formation and evolution of the Galactic bulge and the Milky Way is still a debated subject. Observations of, e.g., the X-shaped bulge, cylindrical stellar motions and young stars in the bulge have suggested that the bulge formed through secular evolution of the disk and not through gas dissipation and/or mergers, as thought previously.\\ Data. We use high-resolution optical spectra of
In this thesis we add a temperature dependence to the newly developed variable polytrope equation of state (Varpoly EOS) from Weppner et al. (2015), making it more universal and more applicable for planetary simulations. In this process we develop a new model for the Gruneisen parameter, which is a parameter that describes how pressure changes with the internal energy. This new model conforms to t
For testing three-dimensional (3D) hydrodynamic models of stellar atmospheres, spectroscopy across spatially resolved stellar surfaces with high spectral resolution is desired. 3D models predict center-to-limb changes in asymmetries, shapes, strengths and wavelength positions of spectral line profiles, reflecting the hydrodynamics of the stellar atmosphere. However, except for a few supergiants an
In the thriving field of exoplanet research new discoveries are made all the time, and while most of the observed systems can be explained with classical planet formation models - some are much harder to explain. When stars form they are often surrounded by the remaining material of the nebulae they formed from. Some of this remaining material forms into a protoplanetary disk around the protostars
A selection of well known period luminosity relations for cepheid variables are studied under the assumption that cepheid variables have a mean vertical velocity of zero in the galactic plane. Proper motion data from Hipparcos and Thyco-2 catalogues are coupled with the distances obtained from applying the period luminosity relations on a database of known classical cepheids to calculate the veloc
In this project I have studied the effect of gas expulsion on the evolution of stellar clusters. What effect the rate of gas removal and the quantity of gas removed has on the evolution on the cluster will be studied through computer simulations with the NBody6 code and compared to analytical predictions. The rate at which gas is removed has a very significant impact on how the cluster evolves
Where the dust in a protoplanetary disk is as the disk evolves over time is essential to know for further studies of the planet formation process. A new star is created alongside a stellar nebula. The nebula contains rock, ice and gas which are not accreted to the star. Our nebula is constructed using the Minimum Mass Solar Nebula model and the column density is studied as the protoplanetary disk
This is an analysis of all the planets at exoplanets.org, with the goal of finding out how many of these that could possibly have moons supporting life. I have first calculated the ranges of the habitable zones (HZ:s) for the stars in the archive, using the Runaway Greenhouse model for the inner limit, and the Maximum Greenhouse model for the outer limit, as presented by Kopparapu et al. (2013A).
Purpose: even in the era of exponential increase in the amount of stellar data gathered, binaries are still often overlooked in observational data due to the special handling they require. The goal of this work is to develop a method capable of automatically and efficiently identifying and extract double-lined spectroscopic binaries (SB2) from a spectroscopic survey, while being scalable and techn
Purpose: In order to study the Galactic Chemical Evolution, elemental abundances are needed. The purpose of this work is to investigate the chemical evolution of the Milky Way by determining several elemental abundances of giants in the local disk. Large surveys are up and coming, and several surveys are already working, and with these, the aim is high quality abundance measurements of several ele
Metal-poor (MP) stars in the Milky Way (the Galaxy) and its satellite galaxies open a window into the earliest times in the history of the Universe, probing the chemistry of the earliest times. Recent galaxy formation simulations predict that the oldest MP stars are those on tightly bound orbits in the inner regions of a galaxy (Tumlinson 2010). Applying this to the Milky Way, MP stars in the bulg
Nucleosynthesis is the mechanism which produces new elements in nuclear reactions. Nuclear reaction rates are highly temperature dependant, and nuclear reactions take place in very hot environments. Current theories predict that the light elements such as hydrogen and helium were produced during the Big Bang. On the other hand, the core of stars produce heavier elements through nuclear fusion. The
Context: The formation of the Galactic Bulge is a topic of active research. There are many scenarios based on observations and Galactic evolution models. The key properties which need to be well constrained observationally are the metallicity distributions of stars and the spatial metallicity gradients. The metallicity distribution of stars in the inner Galactic Bulge (|b|<4o) is a subject of ongo
Context. Large scale chemical abundance gradients in the Galactic disks, small-scale abundance structures, and the mean chemical abundance values in the Solar vicinity, are important constraints to Galactic chemo-dynamical formation and evolution models. The formation and evolution of stars, and interstellar gas and dust depends on the distribution and evolution of matter in the Galaxy. Therefore,
