The circumstellar environment around the extreme Galactic red supergiant NML Cygni: Dense, dusty, and asymmetric

TL;DR

This study characterizes the complex, dusty, and asymmetric circumstellar environment of the extreme Galactic red supergiant NML Cygni, revealing detailed dust and gas properties, morphology, and potential binary interactions through interferometric observations.

Contribution

It provides the first detailed interferometric analysis of NML Cygni's circumstellar environment, uncovering complex morphology, high-velocity components, and possible binary influence.

Findings

Detected two strong continuum components with a total dust mass of ~2×10⁻³ M_⊙.

Measured outflow extent supporting a mass-loss rate of several 10⁻⁴ M_⊙/year.

Identified complex morphology and potential binary companion influence.

Abstract

Supernova observations imply the presence of a dense and asymmetric circumstellar environment around SN Type II progenitors, whereas the mass loss from these progenitors, namely, red supergiants, is still poorly constrained. We aim to characterise the dust and gas in the circumstellar environment of the extreme Galactic red supergiant \nmlcyg in terms of mass, morphology, and kinematics. Based on interferometric observations with NOEMA at 230 GHz we estimated dust masses and temperatures, and measured the extent and morphological complexity of the circumstellar environment. We detected two strong continuum components, amounting to an estimated total dust mass of $\sim2\times10^{-3}M_{\odot}$ located out to ~2000 AU from the star, largely beyond the dust detected at optical/infrared wavelengths. The extent of the detected CO emission supports the notion that the outflow is formed by a mass-loss rate of several $10^{-4}\,M_{\odot}$/year and that it is not primarily shaped by extreme irradiation from the Cyg OB2 cluster it has been associated with. We have detected, but not resolved, previously unseen high-velocity components close to the star. The observations reveal a very complex circumstellar morphology and we propose that some of the detected components could be the imprint of a hitherto unknown binary companion.