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Studies of the Diffuse Interstellar Bands. IV. The Nearly Perfect Correlation Between ??6196.0 and 6613.6
In a sample of 114 diffuse cloud sightlines spanning a wide range ofinterstellar environments, we find the equivalent widths of the diffuseinterstellar bands (DIBs) ?6196.0 and ?6613.6 to beextremely well correlated, with a correlation coefficient of 0.986. Amaximum likelihood functional relationship analysis shows that theobservations are consistent with a perfect correlation if theobservational errors, which are dominated by continuum placement andother systematics such as interfering lines, have been underestimated bya factor of 2. The quality of this correlation far exceeds otherpreviously studied correlations, such as that between the ?5780.5DIB and either the color excess or the atomic hydrogen column density.The unusually tight correlation between these two DIBs would seem tosuggest that they might represent the first pair of DIBs known to be dueto the same molecular carrier. However, further theoretical work will berequired to determine whether the different linewidths and band shapesof these two DIBs can be consistent with a common carrier. If the twoDIBs do not in fact share the same molecular carrier, their two carriersmust be chemically very closely related.
| 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 We started with the unpublished catalog byAllen, Tapia, & Parrao of all the known visual systems having threeor more stars in which the maximum separation is less than 3.0 times theminimum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.
| Distance and density of short lived H I clouds at high galactic latitudes
Very narrow interstellar absorption lines of sodium were detected inspectra of stars in the direction of a strikingly narrow and elongated HI filament, at velocities near -1.2 km/s well correlated with the H Iemission. One of the stars, SAO 30359, additionally shows an opticallystrong interstellar absorption line at V(LSR) = -10 km/s withoutcorresponding H I emission. Here, the results of the opticalobservations are presented. The size and density of a gas clump which isassumed to be responsible for this noncoincident line is derived. Fromthe distance to the stars and the presence of absorption features, anupper distance limit of d = 240 pc is derived for this high-latitude H Ifilament as well as for the gas clump.
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