To the problem of spectral mimicry of supergiants

TL;DR

This paper investigates the spectral mimicry phenomenon where hypergiants and post-AGB supergiants exhibit similar spectra, complicating their classification, and emphasizes the need for multiple parameters to distinguish them.

Contribution

It provides a comprehensive analysis of spectral mimicry using high-quality spectral data and outlines the multi-parameter approach needed for accurate star classification.

Findings

Spectral mimicry occurs between hypergiants and post-AGB stars.

Distinguishing these stars requires analyzing multiple parameters.

Long-term spectral monitoring reveals the complexity of star classification.

Abstract

The phenomenon of spectral mimicry refers to the fact that hypergiants and post-AGB supergiants - stars of different masses in fundamentally different stages of their evolution have similar optical spectra, and also share certain other characteristics (unstable and extended atmospheres, expanding gas-dust envelopes, high IR excesses). As a consequence, it is not always possible to distinguish post-AGB stars from hypergiants based on individual spectral observations in the optical range. Examples of spectral mimicry are presented using uniform, high-quality spectral material obtained on the 6-m telescope of the Special Astrophysical Observatory in the course of long-term monitoring of high-luminosity stars. It is shown that unambiguously resolving the mimicry problem for individual stars requires the determination of a whole set of parameters: luminosity, wind parameters, spectral energy distribution, spectral features, velocity field in the atmosphere and circumstellar medium, behavior of the parameters with time, and the abundances of chemical elements in the atmosphere.