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A Study of A- and B-Type Stars in the Southern Galactic Halo


Pier, Jeffrey Ross (1983) A Study of A- and B-Type Stars in the Southern Galactic Halo. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/s939-dc28.


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-1 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-1 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.))
Subject Keywords:Astronomy
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Astronomy
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Cohen, Marshall H.
Group:Astronomy Department
Thesis Committee:
  • Greenstein, Jesse L. (chair)
  • Mould, Jeremy R.
  • Preston, George W.
  • Cohen, Marshall H.
Defense Date:18 October 1982
Funding AgencyGrant Number
United States Department of Veterans AffairsUNSPECIFIED
Record Number:CaltechETD:etd-09082008-142312
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for Chapter 1.
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:3392
Deposited By: Imported from ETD-db
Deposited On:12 Sep 2008
Last Modified:16 Apr 2021 22:21

Thesis Files

PDF (Pier_jr_1983.pdf) - Final Version
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