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Rotation curve of the Galactic outer disk derived from radial velocities and UCAC3 proper motions of carbon stars

Research in Astronomy and Astrophysics 2010年第6期10卷 541-552页

作者： Jia-Cheng Liu Zi Zhu Department of Astronomy Nanjing University Nanjing 210093 China Key Laboratory of Modem Astronomy and Astrophysics （Nanjing University） Ministry of Education Nanjing 210093 China

The availability of astrometfic data and radial velocities of carbon stars near the Galactic plane enables us to investigate the kinematics of the Milky Way, especially the rotation curve. The recently published Third U. S. Naval Observatory CCD Astrograph Catalog （UCAC3） provides the opportunity to test this problem using three-dimensional velocity in order to obtain more reliable rotation curves. We intend to study the Galactic rotation curve up to 15 kpc using the radial velocities and proper motions of carbon stars. The motivation for using UCAC3 is to provide high precision proper motions which have hardly been used in determining the rotation velocity of tracers. Seventy-four carbon stars and carbon-rich Mira variables toward the anti-center direction （90° 〈 l 〈 270°, ｜b｜〈 6°） are picked up from the literature then matched with UCAC3 carbon star candidates to obtain their proper motions. A rigorous geometrical method is employed to compute the rotation velocity of each object. Taking carbon stars as tracers, we find a flat rotation curve of 210 ± 12 kms^-1 assuming R0 = 8.0kpc for the galactocentric distance and V0 = 220kms^-1 for the rotation velocity of the Sun. Due to the uncertainties of distances, the rotation velocities are more dispersed if tangential velocities enter the calculation, compared to those derived from radial velocities only. However, the whole rotation curve shows coherence with previous results. Increasing observation and study of carbon stars would be desirable in order to provide more homogeneous data for the kinematical study of the Galactic disk.

关键词： astrometry -- galaxy disk -- galaxy kinematics and dynamics -- stars carbon

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Numerical simulation of a possible origin of the positive radial metallicity gradient of the thick disk

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Research in Astronomy and Astrophysics 2014年第11期14卷 1406-1414页

作者： Awat Rahimi Kenneth Carrell Daisuke Kawata National Astronomical Observatories Chinese Academy of Sciences Mullard Space Science Laboratory University College London Holmbury St.Mary DorkingSurrey RH5 6NT UK

We analyze the radial and vertical metallicity and [α/Fe] gradients of the disk stars of a disk galaxy simulated in a fully cosmological setting with the chemo- dynamical galaxy evolution code GCD＋. We study how the radial abundance gradients vary as a function of height above the plane and find that the metallicity （[α/Fe]） gra- dient becomes more positive （negative） with increasing height, changing sign around 1.5 kpc above the plane. At the largest vertical height （2 〈丨z丨〈 3 kpc）, our simulated galaxy shows a positive radial metallicity gradient. We find that the positive metallicity gradient is caused by the age-metallicity and age-velocity dispersion relation, where younger stars have higher metallicity and lower velocity dispersion. Due to the age- velocity dispersion relation, a greater fraction of younger stars reaches 丨z丨〉 2 kpc at the outer region, because of the lower gravitational restoring force of the disk, i.e. flaring. As a result, the fraction of younger stars with higher metallicity due to the age-metallicity relation becomes higher at the outer radii, which makes the median metallicity higher at the outer radii. Combining this result with the recently observed age-metallicity and age-velocity dispersion relation for the Milky Way thick disk stars suggested by Haywood et al., we argue that the observed （small） positive radial metal- licity gradient at large heights of the Milky Way disk stars can be explained by flaring of the younger thick and/or thin disk stars.

关键词： galaxy disk -- galaxy kinematics and dynamics -- galaxies interac-tions- galaxies formation- galaxies evolution- galaxies abundances

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