MASSCLEANcolors - Mass Dependent Integrated Colors for Stellar Clusters Derived from 30 Million Monte Carlo Simulations -

TL;DR

This study uses Monte Carlo simulations to analyze how integrated colors of stellar clusters vary with mass and age, revealing deviations from simple models for low-mass clusters and providing a new tool for better cluster characterization.

Contribution

The paper introduces a Monte Carlo simulation package that quantifies stochastic effects on cluster colors, improving understanding beyond traditional SSP models for low-mass clusters.

Findings

Colors match SSP models for clusters with mass >= 10^6 M_Sun.

Lower mass clusters show less red colors than SSP predictions.

Dispersion in colors increases as cluster mass decreases.

Abstract

We present Monte Carlo models of open stellar clusters with the purpose of mapping out the behavior of integrated colors with mass and age. Our cluster simulation package allows for stochastic variations in the stellar mass function to evaluate variations in integrated cluster properties. We find that UBVK colors from our simulations are consistent with simple stellar population (SSP) models, provided the cluster mass is large, Mcluster >= 10^6 M_Sun. Below this mass, our simulations show two significant effects. First, the mean value of the distribution of integrated colors moves away from the SSP predictions and is less red, in the first 10^7 to 10^8 years in UBV colors, and for all ages in (V - K). Second, the 1\sigma dispersion of observed colors increases significantly with lower cluster mass. The former we attribute to the reduced number of red luminous stars in most of the lower mass clusters and the later we attribute to the increased stochastic effect of a few of these stars on lower mass clusters. This later point was always assumed to occur, but we now provide the first public code able to quantify this effect. We are completing a more extensive database of magnitudes and colors as a function of stellar cluster age and mass that will allow the determination of the correlation coefficients among different bands, and improve estimates of cluster age and mass from integrated photometry.