Observations of debris disks, the products of the collisional evolution of rocky planetesimals, can be used to trace planetary activity across a wide range of stellar types. The most common end points of stellar evolution are no exception, as debris disks have been observed around several dozen white dwarf stars. But instead of planetary formation, post-main-sequence debris disks are a signpost of planetary destruction, resulting in compact debris disks from the tidal disruption of remnant planetesimals. In this work, we present the discovery of five new debris disks around white dwarf stars with gaseous debris in emission. All five systems exhibit excess infrared radiation from dusty debris, emission lines from gaseous debris, and atmospheric absorption features indicating ongoing accretion of metal-rich debris. In four of the systems, we detect multiple metal species in emission, some of which occur at strengths and transitions previously unseen in debris disks around white dwarf stars. Our first year of spectroscopic follow-up hints at strong variability in the emission lines that can be studied in the future, expanding the range of phenomena these post-main-sequence debris disks exhibit.
1. Attention is drawn to the remarkable dissimilarity between the cacao and the grapefruit tree in their nutrient requirements, indicating that grapefruit is calcicolous in physiological habit. This conclusion is mainly based on a consideration of the results of chemical analysis of representative leaf material produced by trees grown on soil of known chemical and physical characteristics, under the same climatic conditions in Trinidad.2. The nutrient relationships that obtain between the cacao and the grapefruit tree respectively and the soil in which they are growing have been gauged by means of chemical analysis of representative leaf material.3. For this purpose, leaf material was obtained from trees growing on the differently manured plots of two large-scale field experiments in Trinidad.
A rapid method is described for the quantitative determination of from 0*001 to 0.01 per cent. of aluminium by means of aluminon. Thioglycollic acid is used as a complexing agent to suppress interference from iron, copper and tin; the pH a t the time of colour development is controlled by the use of a buffer solution. Data pertaining to interference from other metals are given and the method can be modified for the determination of aluminium in certain tin and cadmium-base alloys.
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