On the nature of anomalous reddening of Cygnus OB2 #12 hypergiant

TL;DR

This study investigates the unusually high reddening of the luminous star Cygnus OB2 #12 by mapping interstellar extinction and discovering multiple stellar components, suggesting circumstellar material as the cause.

Contribution

It provides the first detailed extinction map around MT304 and identifies multiple stellar components, indicating circumstellar material influences reddening.

Findings

Extinction increases towards MT304.

Detection of a second stellar component.

Discovery of a third, fainter component.

Abstract

To explain the nature of the anomalously high reddening (Av~10 mag) towards one of the most luminous stars in the Galaxy - Cyg OB2 #12 (B5 Ia-0), also known as MT304, we carried out spectro-photometric observations of 24 stars located in its vicinity. We included five new B-stars to the members of Cygnus OB2, and for five more photometrically selected stars we spectroscopically confirmed their membership. We constructed the map of interstellar extinction within 2.5 arcmin radius and found that interstellar extinction increases towards MT304. The increase of reddening suggests that the reddening excess may be caused by the circumstellar shell ejected by the star during its evolution. We also report the detection of a second component of MT304, and discovery of an even fainter third component, based on data of speckle interferometric observations taken with the Russian 6-m telescope.