Trumpler and Weaver (1953) discuss a systematic error which they attribute to the process of selecting stars by a lower limit in parallax values. The systematic error is introduced because, on the average, the observed parallaxes are larger than the true parallaxes. We demonstrate that the same type of systematic effect exists for all stars with observed trigonometric parallaxes. The problem is treated analytically and can be put in a dimensionless form. The size of the systematic error depends only upon the ratio o/tto where a is the standard deviation of tto, the observed parallax. Corrections are obtained which are to be applied to absolute magnitudes derived from trigonometric parallaxes. The corrected absolute magnitudes are the proper values to use in luminosity calibrations.
A degree-day model was developed for Alberta populations of Ostrinia nubilalis Hübner. Starting with overwintered fifth-instar larvae, the model calculates the temporal distribution of first- and second-instar larvae which are the stages most vulnerable to chemical suppression. Predictions from three alternative models were compared against field data from southern Alberta. Use of a standard 10°C growth threshold to calculate physiological time scales allowed predictions as accurate as those obtained using either a pooled threshold (11.4°C) calculated specifically from Alberta populations, or a model using two thresholds (12.3°C for fifth-instar larvae to adult and 10.2°C for eggs to second-instar larvae) that incorporated significant differences in growth characteristics observed among life stages. We conclude that standard thresholds are sufficient for degree-day models for northern populations of O. nubilalis. The standard model (t0 = 10°C) predicts that moth emergence will peak at ca. 145 degree-days after median pupation, and that numbers of eggs, and first- and second-instar larvae should peak at 200, 310, and 450 degree-days, respectively. Model predictions can be used to time sampling effort in support of management decisions.
Corrections are applied to the absolute magnitudes of the stars used by Wilson (1967) to account for the systematic error discussed by Lutz and Kelker (1973). Several methods of fitting straight lines to data are applied to this sample in an effort to determine the relation between M v and log W 0 . We conclude that this relation is best represented by the equation M v = -17.13 log W 0 + 30.74.
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