[Paper Review] LBV Nebulae: The Mass Lost from the Most Massive Stars

K. Weis|arXiv (Cornell University)|Apr 12, 2001

Astronomy and Astrophysical Research4 citations

TL;DR

This paper investigates luminous blue variable (LBV) nebulae as relics of extreme mass loss in the most massive stars (>50 M☉), analyzing their morphology and kinematics to constrain eruption mechanisms and stellar evolution. It finds that bipolarity is a widespread feature across LBV nebulae, challenging the notion that η Carinae is unique and implying that such asymmetries must be explained by stellar rotation, binary interactions, or asymmetric winds in future models.

ABSTRACT

The most massive stars, with initial masses above ~50M_sun, encounter a phase of extreme mass loss - sometimes accompanied by so-called giant eruptions - in which the stars' evolution is reversed from a redward to a blueward motion in the HRD. In this phase the stars are known as Luminous Blue Variable (LBVs).Neither the reason for the onset of the strong mass loss nor the cause for the giant eruptions is really understood, nor is their implications for the evolution of these most massive stars. I will present a study of the LBV nebulae which are formed in this phase as a consequence of the strong mass loss and draw conclusions from the morphology and kinematics of these nebulae on possible eruption mechanisms and stellar parameters of the LBV stars. The analysis contains a large collection of LBV nebulae which form an evolutionary sequence of LBV nebulae. A special concern will be the frequently observed bipolar nature of the LBV nebulae which seems to be a general feature and presents strong constraints on further models of the LBV phase and especially on the formation mechanism of the nebulae.

Motivation & Objective

• To understand the physical mechanisms driving extreme mass loss and giant eruptions in the most massive stars (>50 M☉).
• To determine the origin and evolution of LBV nebulae formed during the LBV phase through morphological and kinematic analysis.
• To assess whether the bipolar structure observed in many LBV nebulae is a general feature or unique to specific objects like η Carinae.
• To evaluate the implications of nebular kinematics and morphology for the duration and energetics of LBV outbursts.
• To establish a sequence of LBV nebulae based on size, expansion velocity, and evolutionary state to infer the timescales of mass loss events.

Proposed method

• Collected and analyzed a comprehensive sample of known LBV nebulae, including morphological data from Hubble and ground-based telescopes.
• Measured expansion velocities using Doppler shift analysis of emission lines (e.g., Hα, [N II]) from spectroscopic observations.
• Compared nebular structures across different systems to identify common morphological features such as bipolarity and collimated filaments.
• Used kinematic data to estimate nebular ages and infer the duration of mass ejection events, particularly for giant eruptions.
• Evaluated the consistency of observed nebular properties with theoretical models of wind-wind interaction and explosive ejection.
• Applied HST-STIS data to study high-velocity, collimated structures (e.g., 'strings') in η Carinae and other nebulae to probe acceleration mechanisms.

Experimental results

Research questions

• RQ1 What causes the onset of extreme mass loss and giant eruptions in massive stars above 50 M☉?
• RQ2 Why do LBV nebulae frequently exhibit bipolar morphology rather than spherical symmetry?
• RQ3 How do the kinematics and morphology of LBV nebulae relate to the evolutionary state and mass loss history of their central stars?
• RQ4 Can the observed expansion velocities and sizes of LBV nebulae be explained by wind-wind interaction models or do they require explosive ejection mechanisms?
• RQ5 To what extent is the bipolarity of LBV nebulae a universal feature, and what does it imply for the underlying physical mechanisms?

Key findings

• Bipolar morphology is a common feature across LBV nebulae, not unique to η Carinae, indicating a general constraint on formation mechanisms.
• The nebula around HR Carinae is interpreted as an evolved, slower, and larger version of the η Carinae nebula, supporting an evolutionary sequence with ages of 4,000–9,000 years.
• Expansion velocities in LBV nebulae range from ~24 km s⁻¹ (Sk -69° 279) to up to 2,000 km s⁻¹ in the outer ejecta of η Carinae, with high-velocity filaments showing Hubble-type velocity profiles.
• Highly collimated, straight, and rapidly expanding filaments (