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Spectrophotometric Distances - Problem of Interstellar Extinction

Krełowski J., Galazutdinov G. A., Strobel A., Bondar A.

Acta Astronomica

2017

Vol. 67, No. 3

281--296

Distances to 112 hot reddened stars in the thin Galactic disk have been estimated with different methods and, their accuracies have been compared. Also, we have applied the CaII-method to test its relation to trigonometric parallax and the spectrophotometric one. Some interstellar clouds apparently contain especially large size dust grains which cause interstellar gray (neutral) extinction. The latter does not correlate with the typical color extinction and may falsify spectrophotometric distance estimates. We conclude that CaII and TiII based method provides in many cases the most correct and reliable distance estimates to hot, bright, distant stars in the thin disk of the Milky Way - more accurate than obtained with the spectrophotometric method.

Interstellar Silicon Abundance

Gnaciński P.

Acta Astronomica

2003

Vol. 56, No. 4

379--390

We present 34 measurements of silicon gas phase column densities in the interstellar medium. We have used spectra containing the Si II 1808 Å line which were obtained with the Goddard High Resolution Spectrograph (GHRS) aboard the Hubble Space Telescope (HST). Extinction curve parameters are determined for analyzed lines of sight and relation between Si/H ratio and extinction parameters is discussed. We find the abundance of gas phase silicon in diffuse clouds to be lower than the solar value by a factor of four.