Fundamental relations for the velocity dispersion of stars in the Milky Way

We explore the fundamental relations governing the radial and vertical velocity dispersions of stars in the Milky Way, from combined studies of complementary surveys including GALAH, LAMOST, APOGEE, the NASA Kepler and K2 missions, and Gaia DR2. We find that different stellar samples, even though they target different tracer populations and employ a variety of age estimation techniques, follow the same set of fundamental relations. We provide the clearest evidence to date that, in addition to the well-known dependence on stellar age, the velocity dispersions of stars depend on orbital angular momentum Lz, metallicity and height above the plane |z|, and are well described by a multiplicatively separable functional form. The dispersions have a power-law dependence on age with exponents of 0.441±0.007 and 0.251±0.006 for σz and σR respectively, and the power law is valid even for the oldest stars. For the solar neighborhood stars, the apparent break in the power law for older stars, as seen in previous studies, is due to the anti-correlation of Lz with age. The dispersions decrease with increasing Lz until we reach the Sun's orbital angular momentum, after which σz increases (implying flaring in the outer disc) while σR flattens. For a given age, the dispersions increase with decreasing metallicity, suggesting that the dispersions increase with birth radius. The dispersions also increase linearly with |z|. The same set of relations that work in the solar neighborhood also work for stars between 3 < R/kpc < 20. Finally, the high-[α/Fe] stars follow the same relations as the low-[α/Fe] stars

Astronomical spectroscopy on m-type red giant stars / Mohd Hafiz bin Mohd Saadon

Red giant phase is one of the phases in stellar evolutionary tracks. The main focus of the study is to explore the late M-type red giant stars by using astronomical spectroscopy technique. Astronomical spectroscopy method is used in order to understand the chemical abundances and the pattern and characteristics of the spectrum of this type of stars. One of the main characteristics that always being associated with M-type stars is titanium oxide (TiO) molecular spectrum bands. The study has been done to see through different subclasses within the M-type and to observe if there are differences in spectral pattern with each other. Also being observed and analysed is Hα spectral line profile which is to be found at 6562.82 Å as one of the main characteristics of stars. The analysis on Hα spectral profile shows the full width half maximum (FHWM) and equivalent width (EW) for Hα. Also being known from the analysis is the radial velocity of the stars. Several M-type red giant stars were observed from M0 to M6. The data acquisition was done by doing astronomical observation session which had been using 20RC Carbon Truss Ritchey-Chrétien telescope attached to the Paramount-ME Robotic mount, SBIG Self Guided Spectrograph (SGS) with resolution of 1.07 Å per pixel and high resolution Charge-Coupled Device (CCD) camera ST-7E. The IRAF software packages were installed on LINUX interface which was used in data reduction and analysis processes on the collected data. A neon lamp is being used to do the wavelength calibration because of the observable lines of this element are in the higher region of visible wavelength, from 5800 Å to 7500 Å. Briefly, the results show that the dominance of TiO is increasing across the M classs

Observational aspects of globular cluster and halo stars in the GALAH survey

This thesis is a study of the observational aspects of globular cluster and halo stars in the galactic Archaeology with HERMES (GALAH) survey. GALAH is a major astronomical survey project that derives stellar parameters (Teff, logg, [Fe/H]) and up to 30 elemental abundances for a very large sample of stars in the Milky Way from high-resolution spectroscopy. This thesis uses the third GALAH internal data release, which includes over 600 000 stars, to test the validity of GALAH’s reported quantities, especially for cool metal-poor globular clusters and halo stars. We also examine the light-element abundance patterns of stars in globular clusters, which have known peculiarities, to search for stars in the Galactic halo with globular cluster-like abundance patterns, and to chart the age-abundance relation in halo stars using elements that have been reported as particularly useful age indicators.In this first application of GALAH data to globular clusters and halo chemodynamics, we explore the behaviour of 30 elemental abundances for 340 stars in four globular clusters, which are NGC 104, NGC 5139, NGC 6397 and NGC 7099, which we found inconsistencies in the light-element abundances. We also discover that approximately 1% (4/445) of metal-poor halo giants in the sample are likely globular cluster escapees with enhanced [Al/Fe] and depleted [Mg/Fe]. Finally, we chart the age-abundance relations of metal-poor halo giants and identify stars with likely extragalactic origins using their kinematics and abundances