Determination of absorption by Q-method for JHK photometry in embedded clusters

TL;DR

This paper presents a method to determine absorption in embedded clusters using the Q-method with 2MASS photometry, addressing uncertainties and proposing a way to select the correct zero-reddening sequence segment.

Contribution

It introduces a new approach to select the zero-reddening sequence segment based on luminosity function differences, improving absorption estimates in embedded clusters.

Findings

The method can distinguish stars with up to 20% error in absorption assignment.

Simulation shows about 10% of stars are misclassified due to irregular absorption.

The approach effectively separates stars despite absorption irregularities.

Abstract

In this paper we describe the absorption determination by the Q-method for 2MASS photometry ($J$, $H$ and $K_S$ bands). Using the Pleiades and Praesepe stars, we determine the zero-reddening sequence for different values of the color excess ratios $E(J-H)/E(H-K_S)$. In this paper we consider a sequence consisting of two segments, that leads to an uncertainty in the determining of absorption - one value of the Q parameter corresponds to two values of the non-reddened color index. We propose a method to select a segment of the zero-reddening sequence for the main sequence stars of the cluster. The method is based on the difference in the position of stars of different segments in the cluster luminosity function. To test the proposed method, we simulate the luminosity functions of clusters with the non-uniform absorption distribution in the cluster region. With the typical absorption values in embedded clusters, about 10 % of stars are erroneously assigned, but in some cases this fraction can reach 20 %. Thus, despite the fact that irregular absorption distorts the distribution of stars of different segments on the cluster luminosity function, our method allows to separate stars with an error of no more than 20 %.