[Paper Review] A study on the nature of the peculiar supergiant HD101584

Eric J. Bakker, H. J. G. L. M. Lamers+4 more|arXiv (Cornell University)|Sep 21, 1995

Stellar, planetary, and galactic studies2 references3 citations

TL;DR

This study investigates HD101584, a peculiar supergiant, using multi-wavelength photometry and spectroscopy. It identifies a B9II-type star with a low-mass post-AGB origin, a binary companion (likely a white dwarf), and a circumsystem disk, with a mass-loss rate of ~10⁻⁸ M☉ yr⁻¹ and a wind terminal velocity of 100±30 km s⁻¹, explaining the star's unusual UV-optical energy distribution via distinct UV and optical emission components.

ABSTRACT

We present a study of low- and high-resolution ultraviolet, high-resolution optical CAT/CES spectra and ultraviolet, optical and infrared photometry of the peculiar supergiant HD101584. From the photometry we learn that the ultraviolet and optical energy distribution cannot be fitted in a consistent way and we need a model in which the UV and optical energy distribution are formed by different gas. The Geneva photometry is best fitted to a B9II Kurucz model, Teff=12000+-1000K and log g=3.0 +-1.0, with an extinction of E(B-V)=0.49+-0.05. The observed spectral features in the spectrum of HD101584 are classified in eight different categories based on the velocity, shape of profile and the identification. The high-excitation HeI(chi=20.87eV), NII(chi=18.40eV), CII (chi=14.39eV) and NI (chi=10.29eV) optical absorption lines are formed in the photosphere of a late B-star (e.g. B8-9I-II). These absorption lines show radial velocity variations which are attributed to binary motion, with the secondary being a white dwarf or a low-mass main sequence object. The low-excitation P-Cygni lines in the optical and UV are formed in the wind. The number density of absorption lines in the UV is so large that the wind spectrum acts as an iron curtain in front of the B-star. The terminal velocity of the wind of $v_{\infty}=100\pm30$ km~s$^{-1}~$ is consistent with the star being a low-mass post-AGB star and the low effective gravity is attributed to the presence of a nearby, unseen, secondary. We estimate a mass-loss rate of M$\approx 10^{-8}$~M$_{\odot}$~yr$^{-1}$. Narrow absorption and emission lines are observed which are formed in a circumsystem disk with a typical radius of $10^{2} R_{\ast}$.

Motivation & Objective

• To determine the nature and physical properties of the peculiar supergiant HD101584.
• To resolve inconsistencies in its ultraviolet and optical energy distributions.
• To identify the origin of its complex spectral features, including absorption and emission lines.
• To investigate the presence and characteristics of a circumstellar disk and binary system.
• To constrain the mass-loss rate and wind properties of the star.

Proposed method

• Analysis of low- and high-resolution ultraviolet, optical, and infrared photometry to model the energy distribution.
• Use of high-resolution CAT/CES optical spectra to identify and classify spectral features by velocity, profile shape, and ionization potential.
• Modeling of photospheric absorption lines (HeI, NII, CII, NI) to infer stellar parameters and radial velocity variations.
• Interpretation of P-Cygni profiles in UV and optical lines to derive wind terminal velocity and mass-loss rate.
• Identification of narrow absorption and emission lines as signatures of a circumsystem disk at ~10² R*.
• Application of Kurucz model atmospheres (B9II, Teff=12000±1000 K, log g=3.0±1.0) with E(B-V)=0.49±0.05 extinction to fit Geneva photometry.

Experimental results

Research questions

• RQ1 What causes the inconsistent fit between the ultraviolet and optical energy distributions of HD101584?
• RQ2 What is the nature of the radial velocity variations observed in the high-excitation absorption lines?
• RQ3 What is the origin of the dense forest of UV absorption lines and how do they affect the observed spectrum?
• RQ4 What is the physical structure and location of the narrow emission and absorption lines?
• RQ5 What is the mass-loss rate and wind terminal velocity of HD101584, and how do they relate to its evolutionary state?

Key findings

• The UV and optical energy distributions of HD101584 are best explained by two distinct gaseous components: a B9II star and a separate UV-emitting wind or disk.
• The photospheric absorption lines (HeI, NII, CII, NI) indicate a late B-star with Teff=12000±1000 K and log g=3.0±1.0, consistent with a B9II spectral type.
• Radial velocity variations in high-excitation lines point to a binary system with a secondary object, likely a white dwarf or low-mass main sequence star.
• The wind terminal velocity is measured at v∞=100±30 km s⁻¹, consistent with a low-mass post-AGB star.
• The mass-loss rate is estimated at M≈10⁻⁸ M☉ yr⁻¹, indicating moderate mass loss for a post-AGB object.
• Narrow absorption and emission lines originate in a circumsystem disk at a typical radius of 10² R*, with kinematic structure indicating rotation or outflow.