Equivalent Width of the Interstellar Na <scp>i</scp> D₁ and D₂ Absorption Lines for Stars with <i>E</i>(<i>B</i> − <i>V</i>) &lt; 0.15

Abstract New measurements of the equivalent width of the interstellar Na i D 1 and D 2 absorption lines for 62 bright B-type stars with E ( B − V ) &lt; 0.15 are used to recalibrate the relation between these quantities in this low-reddening regime, and to quantify the scatter around this relation. Stars showing multiple components in their interstellar Na i lines clearly show a larger total equivalent width at the same E ( B − V ) than stars with a single interstellar Na i absorption lines. Semi-empirical relations are derived that allow for the reddening toward stars showing single interstellar Na i absorption lines to be estimated. Previous calibrations of this relation are typically found to underestimate E ( B − V ) for these stars.