MSX versus IRAS Two-Color Diagrams and the CSE-Sequence of Oxygen-Rich Late-Type Stars

TL;DR

This paper introduces MSX two-color diagrams as a new tool to characterize circumstellar environments of oxygen-rich stars, improving detection of maser emissions especially in regions where IRAS data is confused.

Contribution

The paper develops MSX two-color diagrams that correlate with IRAS regions, providing a new method to study circumstellar environments and enhance maser survey targeting.

Findings

MSX diagrams effectively characterize circumstellar environments.

Detection rates for SiO masers can reach 60-80% using MSX colors.

Potential error identified in MSX catalog's 21.3 μm band photometry.

Abstract

We present MSX two-color diagrams that can be used to characterize circumstellar environments of sources with good quality MSX colors in terms of IRAS color regions for oxygen-rich stars. With these diagrams we aim to provide a new tool that can be used to study circumstellar environments and to improve detection rates for targeted surveys for circumstellar maser emission similar to the IRAS two-color diagram. This new tool is especially useful for regions in the sky where IRAS was confused, in particular in the Galactic plane and bulge region. Unfortunately, using MSX colors alone does not allow to distinguish between carbon-rich and oxygen-rich objects. An application of this tool on 86 GHz SiO masers shows that for this type of masers an instantaneous detection rate of 60% to 80% can be achieved if target sources are selected according to MSX color (region). Our investigations may have revealed an error in the MSX point source catalog version 2.3. That is, the photometry of the 21.3 $\mu$m (MSX E filter) band for most weak 8.28 $\mu$m (or MSX A filter) band sources seems off by about a factor two (0.5--1 magnitude too bright).