The ISM in O-star spectroscopic surveys: GOSSS, OWN, IACOB, NoMaDS, and CAFÉ-BEANS

Abstract

I present results on the interstellar medium towards the O stars observed in five optical spectroscopic surveys: GOSSS, OWN, IACOB, NoMaDS, and CAFÉ-BEANS. I have measured both the amount [$E(4405-5495)$] and type [$R_{5495}$] of extinction towards several hundreds of Galactic O stars and verified that the Maíz Apellániz et al. (2014) family of extinction laws provides a significantly better fit to optical+NIR Galactic extinction than either the Cardelli et al. (1989) or the Fitzpatrick (1999) families. $R_{5495}$ values are concentrated between 3.0 and 3.5 but for low values of $E(4405-5495)$ there is a significant population with larger $R_{5495}$ associated with H II regions. I have also measured different DIBs and I have found that $W$(5797)/$W$(5780) is anticorrelated with $R_{5495}$, a sign that extreme $\zeta$ clouds are characterized not only by low ionization environments (as opposed to $\sigma$ clouds) but also by having a larger fraction of small dust grains. The equivalent width of the "Gaia DIB" (8621 Å) is strongly correlated with $E(4405-5495)$, as expected, and its behavior appears to be more $\sigma$-like than $\zeta$-like. We have also started analyzing some individual sightlines in detail.

arXiv comment10 pages. To appear in the Memorie della societa astronomica italiana edition dedicated to the EWASS 2015 Special Session 20: 3D structure of the ISM from absorption data in the Gaia Era