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Astron. Astrophys. 318, 269-274 (1997)

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Equivalent width of Na I and K I lines and reddening

Ulisse Munari 1 and Toma Zwitter 2

1 Osservatorio Astronomico di Padova, Sede di Asiago, I-36032 Asiago (VI), Italy (e-Mail: munari@astras.pd.astro.it)
2 University of Ljubljana, Department of Physics, Jadranska 19, 1000 Ljubljana, Slovenia (e-Mail: tomaz.zwitter@uni-lj.si)

Received 18 January 1996 / Accepted 26 June 1996


The profile, radial velocity and equivalent width of the interstellar lines of Na I (5890.0, 5895.9 Å) and K I (7699.0 Å) have been obtained from Echelle+CCD observations at resolving power [FORMULA] 16,500 for 32 O and early B stars suffering from a reddening between [FORMULA] =0.06 and 1.57. The data have been used to search for and calibrate a relation between equivalent width and reddening.

When the interstellar lines show a single and sharp component, useful relations to estimate reddening from equivalent widths have been derived. The relation for Na I is most sensitive in the range 0.0 [FORMULA] 0.4, and the one for K I takes over at higher reddening. Good quality equivalent width measurements allow [FORMULA] to be estimated with an accuracy of about 0.05 mag.

For multi-component profiles of Na I and K I lines the estimate of reddening is more ambiguous with a general scatter of 0.15 mag. Close blends of multiple components allow only an estimate of an upper limit to [FORMULA].

Key words: interstellar medium: atoms – interstellar medium: dust, extinction

Send offprint requests to: U. Munari

© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998