Optical Interstellar Absorption Features

Selective Absorption of Starlight by Interstellar Clouds.

Interstellar absorption lines toward Cep OB4

An analysis of optical echelle spectra towards nine stars in the Cep OB4 association is presented. Interstellar absorption lines which arise in the (1, 0) and (2, 0) bands of the CN A 2Π – X 2Σ+ red system towards BD+66◦ 1661, BD+66◦ 1674, and BD+66◦ 1675 are used to infer accurate CN column densities N(CN). A comparison with earlier measurements in the CN violet system allows to infer a CN Dop...

HI 21 cm - line observations with the GMRT towards interstellar clouds previously seen in optical absorption

We have made HI 21cm-line absorption measurements using the GMRT towards 15 directions in the Galaxy which are known to have high random velocity clouds as seen in the optical absorption lines of CaII and NaI. For the first time, in 6 out of these 15 directions we detect HI absorption features corresponding to the high random velocity optical absorption lines. The mean optical depth of these de...

A Procedure for Correcting the Apparent Optical Depths of Moderately Saturated Interstellar Absorption Lines

Presently, most observations of absorption lines from interstellar and intergalactic matter have sufficient resolution to show most of the structure at differing radial velocities of the absorber. This added information allows one to go beyond the practice of just obtaining equivalent widths. As with measurements of Wλ, however, it is important to sense and correct for the fact that some parts ...

Ultraviolet Interstellar Linear Polarization. Iii. Features

Astro-2 has revealed a broad, weak spectral feature in the ultraviolet interstellar linear polarization for two lines of sight, conÐrming the original detection toward HD 197770 and adding HD 147933È4. These are the only two polarization features found in some 30 lines of sight now observed. Both features are centered close to 2175 the position of the ubiquitous ultraviolet extinction bump. Two...