First observed interaction of the circumstellar envelope of an S-star with the environment of Sgr A*

TL;DR

This study presents the first detailed multiwavelength analysis of the bow shock source X7 near Sgr A*, revealing its nature as a dust-enshrouded stellar object interacting with the environment of the supermassive black hole.

Contribution

It provides the first observational evidence of the interaction between the circumstellar envelope of an S-star and the environment of Sgr A* using multiwavelength data spanning nearly two decades.

Findings

X7 has a velocity of ~200 km/s from tip to tail.

X7 is a dust-enshrouded stellar object with a two-component black-body spectrum.

The gas and dust shell of X7 appears decoupled from its stellar source after 2010.

Abstract

Several publications highlight the importance of the observations of bow shocks to learn more about the surrounding interstellar medium and radiation field. We revisit the most prominent dusty and gaseous bow shock source, X7, close to the supermassive black hole, Sgr~A*, using multiwavelength analysis. For the purpose of this study, we use SINFONI (H+K-band) and NACO ($L'$- and $M'$-band) data-sets between 2002 and 2018 with additional COMIC/ADONIS+RASOIR ($L'$-band) data of 1999. By analyzing the line maps of SINFONI, we identify a velocity of $\sim 200$ km/s from the tip to the tail. Furthermore, a combination of the multiwavelength data of NACO and SINFONI in the $H$-, $K$-, $L'$-, and $M'$-band results in a two-component black-body fit that implies that X7 is a dust-enshrouded stellar object. The observed ongoing elongation and orientation of X7 in the Br$\gamma$ line maps and the NACO $L'$-band continuum indicate a wind arising at the position of Sgr~A* or at the IRS16 complex. Observations after 2010 show that the dust and the gas shell seems to be decoupled in projection from its stellar source S50. The data also implies that the tail of X7 gets thermally heated up due to the presence of S50. The gas emission at the tip is excited because of the related forward scattering (Mie-scattering), which will continue to influence the shape of X7 in the near future. In addition, we find excited [FeIII] lines, which underline together with the recently analyzed dusty sources and the Br$\gamma$-bar the uniqueness of this source.