Mass and luminosity evolution of young stellar objects

TL;DR

This paper presents a model for protostar mass and luminosity evolution in clusters, providing new estimates of cluster age, protostar birthrate, and accretion parameters, aligning well with observed data and offering a simpler age estimation method.

Contribution

The paper introduces a novel model of protostar evolution that estimates cluster parameters directly from protostar and PMS star counts, matching observed luminosity distributions.

Findings

Cluster ages are 1-3 Myr, consistent with other estimates.

Protostar fraction decreases outward, indicating increasing local star-forming age.

The method offers a simpler alternative to optical spectroscopy for age estimation.

Abstract

A model of protostar mass and luminosity evolution in clusters gives new estimates of cluster age, protostar birthrate, accretion rate and mean accretion time. The model assumes constant protostar birthrate, core-clump accretion, and equally likely accretion stopping. Its parameters are set to reproduce the initial mass function, and to match protostar luminosity distributions in nearby star-forming regions. It obtains cluster ages and birthrates from the observed numbers of protostars and pre-main sequence (PMS) stars, and from the modal value of the protostar luminosity. In 31 embedded clusters and complexes the global cluster age is 1-3 Myr, matching available estimates based on optical spectroscopy and evolutionary tracks. This method of age estimation is simpler than optical spectroscopy, and is more useful for young embedded clusters where optical spectrocopy is not possible. In the youngest clusters, the protostar fraction decreases outward from the densest gas, indicating that the local star-forming age increases outward from a few 0.1 Myr in small protostar-dominated zones to a few Myr in large PMS-dominated zones.