Galactic kinematics

In addition to the indication of pollution from SNela (i.e. the knee ) found in the [Mg/Fe] and [O/Fe] trends,for kinematically selected thick disk samples, there is also evidence that thick disk stars well above the galactic plane show the same trend. In Fig. 2 we show the first results of a study of in situ metal-rich thick disk stars. It appears that there might be a downward trend in [Mg/Fe] as a function of [Fe/H] also well above the thin disk. This must, however, be further established before any firm conclusions can be drawn. 

Given that we in principle can never select a sample of local thick disk stars that is guaranteed to not contain any intervening thin disk stars, I would argue that we should keep the selection schemes as simple and as transparent as possible. In this sense the simplest and most robust selection is based on the kinematics of the stars. This is also the least model dependent method. Of course, should positions be available, i.e. height over the galactic plane, these could, and should, be used. 

Abstract. High resolution spectral data of red clump stars towards the NGP have been obtained with the spectrograph Elodie at OHP stars. Nearby Hipparcos red clump stars were also observed. We determine the thin and thick properties kinematics and chemical abundances in the solar neighbourhood. We estimate the surface mass density of the galactic disk, we also determine the thin and thick disk chemical properties. 

Most of these stars are clump giants and span typical distances from 0 pc to 800 pc to the galactic mid-plane. This new sample, free of any kinematical and metallicity bias, is used to investigate the vertical distribution of disk stars. 

It is quite astonishing how little observational information is available on the chemistry and kinematics of the Galactic Bulge. A massive and exciting opportunity for the current multi-object spectrographs is being overlooked here. 

Fig. 3. The 2-D structure of the inner Galactic bar, based on direct photometric analysis of red clump stars as distance indicators. Now these individual bar stars are identified, detailed study of their kinematics and chemical abundances will be possible. Preliminary photometric indications suggest the bar is more closely disk than bulge in its populations. This figure is from Babusiaux Gilmore 2004.

Fig. 1. Variation in [Fe/H] versus Galactic rotational velocity for stars assigned to Galactic stellar populations based purely on their kinematics thin disk (red), thick disk (green), halo (cyan), plunging orbits (blue), extreme retrograde orbits (black).

Figure 8.8 shows a marked increase in the scatter of [a/Fe] as one goes down through [Fe/H] = -0.4, at which point there is also a marked change in kinematic properties, notably the dispersion of velocities W perpendicular to the Galactic... 

Initially we had no idea how we can help Zeldovich. But soon we remembered our previous experience in the study of galactic populations kinematical and structural properties of populations hold the memory of their previous evolution and formation (Rootsmae 1961, Eggen, Lynden-Bell Sandage 1962). 

The sun is located near the edge of the arm O. It may be noted that this picture of the spiral structure in the vicinity of the sun is based on both optical and radio observations, whereas the large scale structure of the interstellar gas (Fig. 4) is based only on observations of the X21 cm hydrogen line and kinematic distances, which become highly uncertain towards the galactic center and anticenter. Kinematic distances are obtained from a model for the rotation of the Galaxy due to Schmidt. This model relates the circular orbital velocity of the gas to the distance from the galactic center (see Fig. 3). 

The kinematics of the R CrB, cool HdC and EHe stars are all similar, being those of an old stellar population strongly concentrated towards the Galactic Centre. They do not share the galactic rotation [136,137]. UW Cen and U Aqr may be in halo orbits. Such a distribution is consistent with a wide range of metallicity. 

Spectropolarimetry has proven to be an important tool in the development of unified theories of active galactic nuclei (AGN). Its strength is that it provides an alternative view of the inner regions of the active nucleus. This allows for the study the stracture and kinematics of both polarizing materials and the emission source. Examples of polarization spectra of two active galaxies NGC 5548 and Was 45 are given in Fig. 15. The observations of NGC 5548 were made in 1997 and Was 45 in 1999 with the 1.2m William Hershel Telescope. 

From radial velocities, together with a model of galactic rotation, one estimates "kinematic" distances (III.l). The line widths and shapes yield information on large-scale motions, turbulence and local electron densities. (II1.3). 

Werner (JPL), Becklin (UCLA), and Hacking (JPL) have detected Fe HI emission in the galactic center with CSHELL. This detection constrains the excitation in the region (near IRS16), but this emission is spatially segregated and kinematically distinct from nearby HI Br 7 emission, another traco of ionized gas. Other investigators have searched for H2, CO, and other molecules in the interstellar medium. 

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