Spectral variability of the IR-source IRAS 01005+7910 optical component

TL;DR

This study analyzes high-resolution optical spectra of IRAS 01005+7910's optical component to determine its spectral type, examine spectral features, and understand its evolutionary status, revealing it mimics a hypergiant but is likely a low-mass post-AGB star.

Contribution

The paper provides detailed spectral analysis of IRAS 01005+7910, identifying its spectral type, velocity variations, and wind characteristics, and clarifies its evolutionary stage as a post-AGB star mimicking a hypergiant.

Findings

Systemic velocity Vsys = -50.5 km/s determined from forbidden emission lines.

Presence of [NII] and [SII] emissions indicates circumstellar ionization onset.

IRAS 01005+7910 exhibits wind profiles typical of hypergiants, but is a low-mass post-AGB star.

Abstract

Highly-resolution optical spectra of the optical component of the IR-source IRAS01005+7910 are used to determine the spectral type of its central star, B1.5$ \pm $0.3, identify the spectral features, and analyze their profile and radial velocity variations. The systemic velocity Vsys =$-50.5$ km/s is determined from the positions of the symmetric and stable profiles of the forbidden [NI], [NII], [OI], [SII], and [FeII] emission lines. The presence of the [NII] and [SII] forbidden emissions indicates the onset of the ionization of the circumstellar envelope and the fact that the star is very close to undergoing the planetary nebula stage. The broad range of heliocentric radial velocity Vr estimates based on the core lines, which amounts to about 34 km/s, is partly due to the deformations of the profiles caused by variable emissions. The variations of the Vr in the line wings are smaller, about 23 km/s, and may be due to pulsations and/or hidden binarity of the star. The deformations of the profiles of complex absorption-emission lines may result from variations of their absorption components caused by the variations of the geometry and kinematics in the wind base. The H$\alpha$ lines exhibit P Cyg III type wind profiles. Deviations of the wind from spherical symmetry are shown to be small. The relatively low wind velocity (27$\div$74 km/s from different observations) and the strong intensity of the red emission (it exceeds the continuum level by up to a factor of seven) are typical for hypergiants rather than the classical supergiants. IRAS01005 +7910 is an example of spectral mimicry of a low mass post-AGB star masquerading as a massive hypergiant.