The Peculiar Nebula Simeis 57: I. Ionized Gas and Dust Extinction

TL;DR

This study provides high-resolution radio maps of the peculiar Galactic nebula Simeis 57, revealing its thermal emission, moderate electron density, and dust extinction properties, contributing to understanding its structure and composition.

Contribution

First detailed radio continuum mapping of Simeis 57 at multiple frequencies, analyzing its thermal emission, dust extinction, and physical properties.

Findings

Radio emission is thermal and optically thin.

Electron density is around 100 cm-3.

Dust extinction varies from 1.0 to 2.8 mag.

Abstract

We present high resolution radio continuum maps of the Galactic nebula Simeis 57 (= HS 191 = G 80.3+4.7) made with the WSRT and the DRAObservatory at frequencies of 609, 1412 and 1420 MHz. At optical and at radio wavelengths, the nebula has a peculiar ``S'' shape, crossed by long, thin and straight filaments. The radio maps, combined with other maps from existing databases, show essentially all radio emission from the peculiar and complex nebula to be thermal and optically thin. Although neither the distance nor the source of excitation of Simeis 57 are known, the nebula can only have a moderate electron density of typically n(e) = 100 cm-3. Its mass is also low, not exceeding some tens of solar masses. Peak emission measures are 5000 pc cm-6.Obscuring dust is closely associated with the nebula, but seems to occur mostly in front of it. Extinctions vary from A(V) = 1.0 mag to A(V) = 2.8 mag with a mean of about 2 mag. The extinction and the far-infrared emission at 100 microns are well-correlated.