A Caltech Library Service

The stellar composition and evolution of irregular and other late-type galaxies


Bagnuolo, William G. (1976) The stellar composition and evolution of irregular and other late-type galaxies. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/84BT-0F97.


The stellar content and history of star formation of a number of Irregular and other late-type galaxies have been analyzed by means of 10-color photometery of the galaxies and a comparison of their colors to the calculated colors of a set of three-parameter models. The galaxy models are assumed to be composed of various amounts of "clusters" from 10[superscript 6] to 10[superscript 10] years old, the colors of which were calculated from stellar-evolutionary tracks and observations of 102 stars of all spectral types. The colors of the model clusters were checked by comparison to the colors of 46 clusters in the Magellanic Clouds.

The first chapter of the thesis gives the principal results of the work, the analysis of the galaxies; the second gives a description of the cluster models and comparison to the cluster observations; the third presents the colors of the 102 calibrating stars.

In the first chapter the colors from 79 observations of 46 different Irregular and other late-type galaxies (mostly Sc's) are given first. The construction of model cluster colors and their behavior as a function of time, t, are briefly discussed. A principal component analysis of the galaxy colors indicates that only three parameters could explain most of the variation in galaxy colors.

Accordingly, a set of three-parameter models is adopted to explain their colors. The three parameters chosen govern the star formation history of the galaxies. The Limber initial mass formation function is assumed. Various two-color plots of some of the galaxy models were made. It is found that the loci of the models agree well with observations. Finally, fits to individual galaxies in the three parameters are made, as well as estimates of the "uniqueness" of the fits. The average difference between the best-fitting parameters of Irregulars and Sc's is interpreted to mean that Irregulars have both relatively more star formation in the recent past and an initial mass formation function enriched in massive stars compared to the Sc's. An irregular rate of star formation in the recent past (t <10[superscript 8] yr) is also indicated.

The second chapter describes the construction of cluster models and a comparison between the model colors and the colors of 46 clusters in the Magellanic Clouds. Cluster models are found to fit observations well in general. Furthermore, the observations permit estimates of n[subscript b]/n[subscript r], the ratio of blue to red supergiants, to be obtained for stars of 3 to 20 solar masses.

The third chapter gives a description of the observation of 102 stars of all luminosity classes and spectral types from O5 to M6. The behavior of the colors of stars of different luminosity classes as functions of assumed log T[subscript e] and spectral type are discussed.

Item Type:Thesis (Dissertation (Ph.D.))
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Astronomy
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Sargent, Wallace L. W.
Group:Astronomy Department
Thesis Committee:
  • Unknown, Unknown
Defense Date:23 January 1976
Record Number:CaltechETD:etd-09082008-143633
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:3393
Deposited By: Imported from ETD-db
Deposited On:12 Sep 2008
Last Modified:20 Dec 2019 19:53

Thesis Files

PDF (Bagnuolo_wg_1976.pdf) - Final Version
See Usage Policy.


Repository Staff Only: item control page