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What is a high dispersion spectrum?

From what I understand it has to do with detecting where absorptions lines are begin generated within the star, and then using the information to adjust the spectrograph to detect the full black body spectrum of the star.

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A "high dispersion" spectrum just means dispersing the light from a star across a large number of detector elements/pixels per unit wavelength.

With more pixels per unit wavelength, you are able to make better measurements of the strengths of absorption/emission lines (because it is more obvious what is continuum and what is line) and you can also make measurements of by how much the absorption/emission lines are broadened - for instance by the rotation of a star - and you are also able to make more precise measurements of the wavelengths of absorption lines, allowing more precise estimates of Doppler shifts.

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Dispersion is basically the spectral equivalent to image resolution: How much/little information do you pack into one pixel. Higher dispersion/resolution allows for more detail, but requires more light to not be noisy/grainy, because a smaller fraction of the total light gets into each pixel. Lower resolution gives less detail, but gives a stronger signal in each pixel, which makes it better for fainter sources, where the high dispersion spectra would just be too noisy to give any useful information.

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