Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aj....109.1682l&link_type=abstract
Astronomical Journal (ISSN 0004-6256), vol. 109, no. 4, p. 1682-1696
Astronomy and Astrophysics
Astronomy
192
Galactic Evolution, Galactic Structure, Infrared Imagery, Pre-Main Sequence Stars, Star Clusters, Star Formation, Star Formation Rate, Stellar Luminosity, Near Infrared Radiation, Star Distribution, Stellar Color, Stellar Mass Accretion, Stellar Models
Scientific paper
We present the results of a sensitive near-infrared (JHK) imaging survey of the young cluster IC 348 and a nearby control field. From comparison of the cluster and control field observations we estimate that 380 sources, the majority of the stars observed in the cluster field, are members of the cluster. The spatial density of these stars is found to be significantly larger than that typical of the classical open clusters but comparable to that which characterizes young embedded clusters such as NGC 2024 and the Trapezium. Overall, we find the surface density distribution of stars in IC 348 to be centrally concentrated and to decrease inversely with the distance from the inner (r approximately 0.1 pc) to the outer (r approximately 1.0 pc) regions of the cluster. In detail the stellar surface density distribution of this cluster exhibits significant structure. Roughly half the stars are contained within a central subcluster with a radius of 0.5 pc. Outside this half-mass radius we identify eight small subclusters which contain 10-20 stars and have radii 0.1-0.2 pc in extent. We construct the K luminosity function (KLF) for IC 348 and find it to increase with magnitude in a nonlinear, power-law fashion in the range 8 less than or equal mK less than or equal 11 mag. We construct evolutionary models for the near-infrared luminosity functions of young (taucl less than or equal 107 yr) star clusters containing pre-main-sequence stars. We find that the KLFs of very young synthetic clusters evolve in a systematic and predictable manner as the clusters age. In general we find that the luminosity functions of young clusters broaden with age. For coeval models (i.e., tausf much less than taucl) the slopes of the power-law portion of the KLFs exhibit significant variation with time, while models with continuous star fromation (i.e., tausf approximately taucl) maintain more or less constant slopes as they age. From comparison of four models with our observations of IC 348 we conclude that star formation in IC 348 has been a continuous process over the last 5-7 X 106 yr and that the overall rate of star formation and the rate of star formation as a function of mass has been constant over the cluster lifetime. From a comparative analysis of published observations of the Trapezium cluster with our models and observations of IC 348, we find that the underlying mass function of both clusters is similar to the IMF for field stars down to the hydrogen burning limit with little evidence for a significant population of single, lower mass objects (brown dwarfs). In addition we also find that despite the similarities in their mass functions, stellar densities, and sizes, IC 348 and the Trapezium have been characterized by significantly different rates of star formation over their lifetimes. The rate of star formation in the younger trapezium cluster has been a factor of 20 greater than that in IC 348. Finally, analysis of the JHK colors of the stars in IC 348 reveals that approximately 20% of the cluster sources are infrared excess sources.
Lada Charles J.
Lada Elizabeth A.
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