Investigating silicate, carbon, and water in the diffuse interstellar medium: the first shots from WISCI

S. T. Zeegers, Jonathan P. Marshall, Karl D. Gordon, Karl A. Misselt, G. P. P. L. Otten, Jeroen Bouwman, Jean Chiar, Marjorie Decleir, Thavisha Dharmawardena, F. Kemper, Aigen Li, Mayank Narang, Alexey Potapov, Manoj Puravankara, Peter Scicluna, Himanshu Tyagi, Eleonora Zari, ChuanYu Wei, Lex Kaper, Frank Backs, Stefan T. Bromley, Laurie Chu, Elisa Costantini, T. R. Geballe, Joel D. Green, Chamani Gunasekera, Burcu Günay, Thomas Henning, Olivia Jones, Joan Mariñoso Guiu, Melissa McClure, Yvonne J. Pendleton, Julia C. Roman-Duval, Tomer Shenar, Alexander G. G. M. Tielens, L. B. F. M. Waters

Published 2025-06-24Version 1

The dusty interstellar medium (ISM) of the Milky Way is distributed in a complex, cloudy structure. It is fundamental to the radiation balance within the Milky Way, provides a reaction surface to form complex molecules, and is the feedstock for future generations of stars and planets. The life cycle of interstellar dust is not completely understood, and neither are its structure nor composition. The abundance, composition, and structure of dust in the diffuse ISM can be determined by combining infrared, optical and ultraviolet spectroscopy. JWST enables measurement of the faint absorption of ISM dust grains against bright stars at kiloparsec distances across the infrared spectrum. Here we present an overview of the project `Webb Investigation of Silicates, Carbons, and Ices' (WISCI) along with interpretation of two targets, GSC 08152-02121 and CPD-59 5831. Observations of 12 WISCI target stars were taken by JWST, the Hubble Space Telescope, Himalayan Chandra Telescope, and the Very Large Telescope. We use these to characterize the targets' spectral types and calculate their line-of-sight extinction parameters, $A_{\rm V}$ and $R_{\rm V}$. We find absorption in the JWST spectra of GSC 08152-02121, and CPD-59 5831 associated with carbonaceous dust around 3.4 and 6.2 micron and amorphous silicates at 9.7 micron. In GSC 08152-02121 we also find indications of absorption by trapped water around 3 micron. This first look from WISCI demonstrates the line-of-sight variability within the sample, and the program's potential to identify and correlate features across ultraviolet to mid-infrared wavelengths.