Open Accessδ Orionis: further temporal variability and evidence for small‐scale structure in the interstellar medium
Author(s) -
Price R. J.,
Crawford I. A.,
Howarth I. D.
Publication year - 2001
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2001.04055.x
Subject(s) - physics , interstellar medium , astrophysics , scale (ratio) , astronomy , galaxy , quantum mechanics
We report here the detection of both spatial and temporal variations in interstellar absorption in the line of sight to δ Orionis. First, we present new high‐resolution (R≈110 000) observations of the interstellar D lines of Na i towards both δ Ori A and C. Comparison of these spectra highlights variations in absorption between the two stars, indicative of small‐scale spatial structure in the interstellar medium in this direction over distances of less than ≈15 000 au (the projected separation of the two stars). Components with the largest Na i column densities and lowest velocity dispersions are, in general, found to be subject to the greatest differences; in fact the narrowest component detected is only observed in one of the sightlines. This effect has also been reported by Meyer & Blades. Secondly, we present new ultra‐high‐resolution (R≈900 000) Na i D 1 observations and high‐resolution (R≈110 000) Ca ii H & K observations of δ Ori A which, through ultra‐high‐resolution work conducted between 1994 and 2000, has been shown to exhibit a time‐variable interstellar Na i absorption component. These new observations, while revealing the further reduction in intensity of the time‐variable Na i absorption, indicate constant Ca ii absorption over the same period. This results in a dramatic reduction in the Na°/Ca + abundance ratio, perhaps indicating the line of sight to be gradually probing a less‐dense outer region of an absorbing filament.