Additionally, the subtracted continuum value is normalized with a reference spectrum of a pre-selected aperture with few emission-line features, using the same bandpasses. The initially offset bandpasses are thereafter shifted away from the layer as needed in such a way that telluric and emission lines are avoided. The total width of the red and blue bandpasses is set using the parameter cwidth either bandpass is skipped for the bluest (lowest) and reddest (highest) pixels. Two narrow bandpasses, a blue and a red bandpass, are offset from the current wavelength (layer) towards bluer (lower) and redder (higher) pixels, beginning at an initial offset ( offset).
The algorithm is first described in the paper mentioned in the Links section below. In comparison to the imaging approach, the narrow "filters" represented by the bandpasses should make it possible to detect fainter objects!
Such an approach can work with PNe as they emit nearly all their intensity in a few emission lines where the forbidden emission line of oxygen, 5007, is typically the strongest one.Īstro-d11 (DELF) presents an alternative approach where a data cube based on integral-field spectroscopy observations provides means to use two very narrow bandpasses near the emission line when subracting the background signal. In that approach, the region is observed both on-band and off-band using narrow bandpass filters a comparison between the two images reveals objects such as PNe. The usual approach to find point sources such as planetary nebulæ (PNe) in astronomical observations has been to observe the object region using imaging techniques. Apply a Differential Emission Line Filter (DELF) to an astronomical spectrum data cube.
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