Date of Award

10-1992

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Astrophysics

Supervisor

D. L. Welch

Abstract

The dynamics of three populous Large Magellanic Cloud (LMC) star clusters NGC 1866, NGC 1978, and NGC 1850, have been examined using a combination of BV charge-coupled device (CCD) images and high-precision radial velocities of individual member stars.

NGC 1866.

V-band CCD images of the young LMC cluster NGC 1866 out to a projected radius R ~ 100 pc were obtained using the 1.0m telescope at Las Campanas. The luminosity profile is described by a power-law. The total cluster luminosity is LV∞ = 6.5 ± 0.3 × 10⁵ L. In the region 4 ≤ R (pc) ≤ 12, the cluster has a mean ellipticity of ε = 0.17 ± 0.06 and a minor axis position angle α = 125° ± 5°. NGC 1866 has a systemic velocity of Vαve = 301.2 ± 1.0 km s⁻⁻¹ and is rotating around an axis at a position angle of 100±25° with a peak velocity of 1.3 ± 0.5 km s⁻¹. The best estimate for the average slope of the mass function is x = 1.3 ± 0.15 (r = 2.0 x 10⁸ years). NGC 1978. BC CCD images of the elliptical LMC cluster NGC 1978 out to a projected radius R ~ 100 pc were obtained using the 1.0m telescope. After star-subtraction and median-filtering the ellipticity of the surface brightness distribution was determined to be ε = 0.30 ± 0.03 and the major axis position angle to be PA = 152 ± 7°. Single and multi-mass anisotropic King-Michie models and single-mass rotating and non-rotating oblate spheroid models were fitted to both the surface luminosity profiles and the radial velocity data. The total cluster luminosity is Lʙ = 3.1-3.7 ± 0.2x10⁵ Lʙ⊙ and Lv = 3.0-3.5 ± 0.2x10⁵ Lv⊙. The single-mass models tended to give better agreement with the luminosity profiles. We found no significant differences between the M/L's derived with oblate spheroid models and those derived with spherical models. NGC 1850. In this thesis we have examined the age and internal dynamics of the young binary LMC cluster NGC 1850. Isochrone fits to a BV color-magnitude diagram revealed that the primary cluster has an age of τ = 90 ± 30 Myr. The total cluster luminosity varied from Lʙ = 2.60-2.65x10⁶ Lʙ⊙ and Lv = 1.25-1.35x10⁶. Of the 52 stars with echelle spectra, a subset of 36 were used to study the cluster dynamics. Values for the slope of the mass function were determined using the derived M/L, theoretical mass-luminosity relationships, and several forms for the IMF. (Abstract shortened by UMI.)

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