Pier, Jeffrey Ross (1983) A study of A- and B-type stars in the southern galactic halo. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-09082008-142312
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A sample of over 200 stars of spectral types A and B has been selected for study. Drawn from the Preston and Shectman objective-prism survey of the southern galactic halo, the stars comprise a sample of halo objects selected without kinematic bias. Photoelectric UBV photometry has been obtained and the sample stars have apparent V magnitudes mostly in the range 13.5 […] V […] 15.5. The (U-B)--(B-V) two-color diagram shows that the halo AB stars have colors similar to those of globular cluster blue horizontal-branch (BHB) stars.
Reticon spectroscopy of the sample confirms the BHB status of the large majority of the sample. Interesting non-BHB stars found include a few high luminosity A stars, several stars of low metallicity and apparently normal main-sequence gravities which may be field Population II blue stragglers, and ten metallic-line stars. A few normal A stars have been found as far as 2 to 3 kpc from the plane, but none beyond that distance. It is suggested that the metal-rich early-type population found by other authors belongs to a population of old disk stars with a scale height of over 1 kpc.
Interstellar Ca II K lines are found in many of the high-velocity stars. The interstellar components arise from low-velocity material associated with the disk.
The solar motion of the halo AB stars is -236 […] 39 km s[…] and the velocity ellipsoid is elongated towards the galactic center throughout the halo. By adding a list of halo objects drawn from other sources and solving for the solar motion a lower limit of -208 […] 20 km s[…] is set for the circular velocity at the solar radius. The solar motion solution is found to be metallicity-dependent. Anisotropy in the velocity ellipsoid is strongly indicated for the combined halo objects. The presence of this global anisotropy removes one of the arguments favoring a flattened halo. Since the gravitational potential of the disk increases the z component of velocity it is seen that at very early times in the history of the Galaxy the velocities were highly anisotropic (predominantly radial).
|Item Type:||Thesis (Dissertation (Ph.D.))|
|Degree Grantor:||California Institute of Technology|
|Thesis Availability:||Restricted to Caltech community only|
|Defense Date:||18 October 1982|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Imported from ETD-db|
|Deposited On:||12 Sep 2008|
|Last Modified:||26 Dec 2012 02:59|
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