[Paper Review] Unveiling the structure and kinematics of B[e] stars' disks from FEROS and CRIRES spectra

M. F. Muratore, W. J. de Wit+6 more|arXiv (Cornell University)|Dec 19, 2012

Astrophysics and Star Formation Studies3 citations

TL;DR

This study uses high-resolution FEROS (optical) and CRIRES (near-infrared) spectroscopy to investigate the kinematics and structure of circumstellar disks around B[e] stars. It finds that forbidden [O i] and [Ca ii] lines indicate Keplerian rotation in most stars, while CO bandheads suggest high-velocity outflows or rotation, with projected velocities comparable to optical lines—challenging assumptions about disk structure and prompting further modeling of line formation conditions.

ABSTRACT

We are investigating the circumstellar material for a sample of B[e] stars using high spectral resolution data taken in the optical and near-infrared regions with ESO/FEROS and ESO/CRIRES spectrographs, respectively. B[e] stars are surrounded by dense disks of still unknown origin. While optical emission lines from [O I] and [Ca II] reflect the disk conditions close to the star (few stellar radii), the near-infrared data, especially the CO band emission, mirror the characteristics in the molecular part of the disk farther away from the star (several AU). Based on our high resolution spectroscopic data, we seek to derive the density and temperature structure of the disks, as well as their kinematics. This will allow us to obtain a better understanding of their structure, formation history and evolution. Here we present our preliminary results.

Motivation & Objective

• To determine the kinematics and physical structure of circumstellar disks around B[e] stars using high-resolution spectroscopy.
• To distinguish between rotational and outflow-driven motions in the disk by analyzing forbidden optical lines and molecular CO bands.
• To constrain the density and temperature structure of the disk by modeling line luminosities and profiles.
• To understand the formation and evolution of B[e] star disks by comparing emission from different regions (inner dense disk to outer molecular zones).

Proposed method

• Obtained high-resolution optical spectra (R ~ 48,000) with FEROS on the ESO 2.2-m telescope in La Silla, covering 3600–9200 Å.
• Acquired high-resolution near-infrared spectra (R ~ 50,000) with CRIRES on the VLT in Paranal, covering 2.276–2.326 μm.
• Applied telluric and heliocentric velocity corrections to both optical and infrared data sets.
• Used the model of Kraus et al. (2000) to fit CO bandhead profiles and derive projected line-of-sight velocities.
• Analyzed double-peaked line profiles of [O i] 6300 Å, [Ca ii] 7291/7324 Å to infer kinematical broadening mechanisms.
• Compared peak separations in forbidden lines and CO bandheads to assess consistency between inner and outer disk kinematics.

Experimental results

Research questions

• RQ1 What is the dominant kinematical mechanism (rotation vs. outflow) responsible for the broadening of forbidden optical emission lines in B[e] stars?
• RQ2 How do the kinematics of the inner disk (traced by [O i] and [Ca ii]) compare to those of the outer molecular disk (traced by CO bandheads)?
• RQ3 What is the spatial distribution of temperature and density in the circumstellar disk, as inferred from line luminosities and profiles?
• RQ4 Why do CO bandhead velocities appear comparable to or higher than those of optical forbidden lines, despite the CO forming at larger radii?

Key findings

• The [Ca ii] 7291 and 7324 Å lines show peak separations of 30–94 km s⁻¹, indicating significant kinematic broadening consistent with rotation or outflow.
• For CPD-52 9243, the [Ca ii] and [O i] line profiles suggest an equatorial outflow scenario, while other stars show kinematics more consistent with Keplerian rotation.
• The CO bandhead emission in the near-infrared shows projected velocities (v_los) of up to 150 km s⁻¹, comparable to the optical line widths.
• The CO bandhead profiles are best fit by models assuming rotation or outflow, with the molecular ring likely located at larger radii than the gaseous disk.
• The similarity in velocity scales between the optical and infrared lines is surprising, as CO forms farther from the star, suggesting possible dual outflowing structures or observational discrepancies due to epoch differences.
• The [Ca ii] lines are likely formed at higher densities and closer to the star than [O i] lines, as suggested by Aret et al. (2012), supporting a layered disk structure.