The role of theta Oph in the formation and evolution of the Pipe Nebula - is star formation ever isolated?

TL;DR

This paper investigates whether the Pipe Nebula's formation and evolution are influenced by the B2 IV star theta Ophiuchi, proposing it as an HII region shell and exploring implications for isolated star formation.

Contribution

It presents a detailed analysis combining observations and radiative transfer modeling to explain the nebula's current state and its potential future star formation triggers.

Findings

The nebula's size, mass, and pressure are consistent with an HII region shell driven by theta Ophiuchi.

The Pipe Nebula is best described as a three-phase medium in pressure equilibrium.

Star formation may be triggered by feedback from collapsing cores or theta Ophiuchi's supernova.

Abstract

We propose that the Pipe Nebula is an HII region shell swept up by the B2 IV beta Cephei star theta Ophiuchi. After reviewing the morphological evidence by recent observations, we perform a series of analytical calculations. We use realistic HII region parameters derived with the radiative transfer code Cloudy from observed stellar parameters. We are able to show that the current size, mass and pressure of the region can be explained in this scenario. We investigate the configuration today and come to the conclusion that the Pipe Nebula can be best described by a three phase medium in pressure equilibrium. The pressure support is provided by the ionized gas and mediated by an atomic component to confine the cores at the observed current pressure. In the future, star formation in these cores is likely to be either triggered by feedback of the most massive, gravitationally bound cores as soon as they collapse or by the supernova explosion of theta Ophiuchi itself.