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The Maximum Age of Trapezium Systems
We sought to determine the maximum age of Trapezium systems by studyingpossible trapezium systems that were selected independently of theiroccurrence in H II regions. We started with the unpublished catalog byAllen, Tapia, & Parrao of all the known visual systems having threeor more stars in which the maximum separation is less than 3.0 times theminimum separation. Their catalog has 968 such systems whose mostfrequent primary type is F, which does not describe young systems. Witha CCD on the Kitt Peak 0.9 m telescope we obtained UBV frames for 265systems accessible with our equipment on Kitt Peak. The frames were usedto obtain UBV photometry for about 1500 stars with an accuracy of+/-0.04 mag between V=7 and 14 mag. Also these frames were used toobtain astrometry with an accuracy of +/-0.015d in position angle and+/-0.01" in separation. For the brightest star in each system weobtained a spectral type to determine the distance and reddening to thesystem. The measures were used to determine physical membership fromstars that (1) fit a single color-magnitude diagram, (2) fit a commoncolor-color diagram, and (3) show no astrometric motion compared tovisual measures made (mostly) a century ago. Combining the results withspectroscopic data for 20 additional Allen et al. systems by Abt, wefound that 126 systems had only optical companions to the primaries, 116systems contained only a single physical pair, 13 were hierarchicalsystems with 3-6 members and having separation ratios of more than afactor of 10, two were small clusters, and only 28 fitted the criteriaof Trapezium systems. However, as shown by Ambartsumian, about 9% of thehierarchical systems should appear to be Trapezium systems inprojection. Those, like other hierarchical systems, have a broaddistribution of primary spectral types. We isolated 14 systems that seemto be true Trapezium systems. They have primary types of B3 or earlier,indicating a maximum age of about 5×107 yr. This upperlimit is consistent with the estimate made by Allen & Poveda for anage of several million years for these dynamically unstable systems.These Trapezia are also large with a median radius of 0.2 pc and amaximum radius of 2.6 pc. We asked why the sample of 285 possibleTrapezium systems yielded only 14 true ones, despite the attempt made byAllen et al. to eliminate optical companions with a ``1% filter,'' i.e.,demanding that each companion have less than a 1% chance of being afield star of that magnitude within a circle of its radius from theprimary. The explanation seems to be that the double star catalogs arebased mostly on BD magnitudes that, fainter than V=12 mag, aresystematically too faint by 1 mag.
| Identification of 106 new infrared carbon stars in the IRAS Point Source Catalog - Near-infrared photometry and their space distribution in the galaxy
A method based solely on IR colors - the combination of near-IR and IRAScolors - is used to identify 106 new IR carbon stars (IRCS). It is shownthat the proportion of IRCS in a region of the IRAS two-color diagrampreviously thought to contain the largest concentration of such stars isnot as large as expected for the faintest objects. A local spatialnumber density of about 12 IRCS/sq kpc is estimated. It is shown to beuniform within 5 to 11 kpc from the galactic center. The local ratio ofIRCS to optical carbon stars is found to be about 35 percent. A totalrestitution rate of about 10 to the -4 solar masses/yr/sq kpc isderived. The efficiency of the combination of near and mid-IR photometryfor the study of AGB stars is confirmed.
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