Journal Article

An empirical relation between sodium absorption and dust extinction

Dovi Poznanski, J. Xavier Prochaska and Joshua S. Bloom

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 426, issue 2, pages 1465-1474
Published in print October 2012 | ISSN: 0035-8711
Published online October 2012 | e-ISSN: 1365-2966 | DOI:
An empirical relation between sodium absorption and dust extinction

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Dust extinction and reddening are ubiquitous in astronomical observations and are often a major source of systematic uncertainty. We present here a study of the correlation between extinction in the Milky Way and the equivalent width of the Na i D absorption doublet. Our sample includes more than 100 high-resolution spectra from the Keck telescopes and nearly a million low-resolution spectra from the Sloan Digital Sky Survey (SDSS). We measure the correlation to unprecedented precision, constrain its shape and derive an empirical relation between these quantities with a dispersion of the order of 0.15 mag in E(BV). From the shape of the curve of growth we further show that a typical sight line through the Galaxy, as seen within the SDSS footprint, crosses about three dust clouds. We provide a brief guide on how to best estimate extinction to extragalactic sources such as supernovae, using the Na i D absorption feature, under a variety of circumstances.

Keywords: ISM: atoms; dust, extinction

Journal Article.  6948 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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