The enormous outer Galaxy HII region CTB 102

TL;DR

This paper reports new radio observations of the large, previously unstudied HII region CTB 102, estimating its physical properties, size, and morphology, and proposing a stellar wind bubble model as an explanation.

Contribution

It provides the first detailed radio recombination line analysis of CTB 102 and introduces a stellar wind bubble model to explain its observed features.

Findings

CTB 102 is approximately 4.3 kpc away.

Its size is estimated to be 100-130 pc, making it one of the largest known HII regions.

A stellar wind bubble model explains its morphology and velocities.

Abstract

We present new radio recombination line observations of the previously unstudied HII region CTB 102. Line parameters are extracted and physical parameters describing the gas are calculated. We estimate the distance to CTB 102 to be 4.3 kpc. Through comparisons with HI and 1.42 GHz radio continuum data, we estimate the size of CTB 102 to be 100-130 pc, making it one of the largest HII regions known, comparable to the W4 complex. A stellar wind blown bubble model is presented as the best explanation for the observed morphology, size and velocities.