Young open clusters as probes of the star formation process

Details Young open clusters as probes of the star formation process Young open clusters as probes of the star formation process

Sep 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt.........1p&link_type=abstract

Ph.D. Thesis Boston Univ., MA.

Astronomy and Astrophysics

Astronomy

1

Mathematical Models, Milky Way Galaxy, Open Clusters, Sky Surveys (Astronomy), Star Formation, Astronomical Photometry, Binary Stars, Cepheid Variables, Disk Galaxies, Stellar Magnitude, Stellar Mass

Scientific paper

The star formation history of a region in the Perseus spiral arm of our Galaxy was explored using digital photometry, in the UBV system, of 23 open clusters. Magnitudes and colors of 35,788 stars were measured, making this the most comprehensive, homogeneous, single study of open cluster properties in one part of the Galaxy. The improved knowledge of the spatial distribution and formation sequence of the clusters, coupled with other studies of radial velocities, proper motions, and gas distribution in the region, strongly suggests that the majority of these clusters were formed during the impact of a high velocity cloud (HVC) with the Galactic disk. HVC's were detected in this region and predictions of a recently published theoretical model of an HVC impact with the disk agree with the observational data extremely well. While it was suggested that HVC impacts can trigger star formation, this is the first time that star formation can be directly connected to such an event. Mass functions for 8 of the clusters were calculated for stars more massive than the Sun, covering a region of the initial mass function (IMF) inaccessible through studies of field stars. These data indicate that, to about one solar mass, the mass functions of clusters, on average, are the same as the so-called 'Salpeter field star IMF'. Deviations do occur, however, with evidence for a deficiency of low mass stars in several clusters. A dip in the IMF at a mass about 1.4 times that of the Sun is detected, at various levels of statistical significance, in six of the clusters. Variations in binary content were seen, although no obvious correlation with cluster age, mass, or size is found. This result has implications for theories of the formation of binary stars. Other uses of this data base are discussed, including an improvement in the cluster age/gas-content relation, and potential improvement in the Cepheid star period-luminosity relation, since previous studies have associated Cepheids with 3 of the clusters in this survey.

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