Capture of field stars by giant interstellar clouds: the formation of moving stellar groups

TL;DR

This paper presents a model explaining the formation of moving stellar groups through the capture of field stars by giant interstellar clouds, involving phases of acceleration, star formation, and gas loss, with analytical solutions showing about 4% of passing stars are captured.

Contribution

The study introduces an analytical model of star capture by giant clouds during their evolution, explaining the origin of moving stellar groups with a specific capture efficiency.

Findings

Approximately 4% of passing stars are captured by the cloud.

The model can account for the formation of moving stellar groups with similar ages.

The Sun could have been captured by the same cloud that formed local moving groups.

Abstract

In the solar neighbourhood, there are moving groups of stars with similar ages and others of stars with heterogeneous ages as the field stars. To explain these facts, we have constructed a simple model of three phases. Phase A: a giant interstellar cloud is uniformly accelerated (or decelerated) with respect to the field stars during a relatively short period of time (10 Myr) and the cloud's mass is uniformly increased; phase B: the acceleration (or deceleration) and mass accretion of the cloud cease. The star formation spreads throughout the cloud, giving origin to stellar groups of similar ages; and phase C: the cloud loses all its gaseous component at a constant rate and in parallel is uniformly decelerated (or accelerated) until reaching the initial velocity of phase A (case 1) or the velocity of the gas cloud remains constant (case 2). Both cases give equivalent results. The system equations for the star motions governed by a time-dependent gravitational potential of the giant cloud and referred to a coordinate system co-moving with the cloud have been solved analytically. We have assumed a homogeneous spheroidal cloud of fixed semi-major axis a=300 pc and of an initial density of 7 at cm^{-3}, with a density increment of 100 per cent and a cloud's velocity variation of 30 km s^{-1}, from the beginning to the end of Phase A. The result is that about 4 per cent of the field stars that are passing within the volume of the cloud at the beginning of phase A is captured. The Sun itself could have been captured by the same cloud that originated the moving groups of the solar neighbourhood.