Variability in the CO ro-vibrational lines from HD163296

TL;DR

This study compares multi-epoch CO ro-vibrational emission lines from HD163296, revealing variability in line shapes and widths, and explores potential causes like disc winds or episodic accretion, supported by thermo-chemical modeling.

Contribution

First direct multi-epoch comparison of CO ro-vibrational lines from HD163296, linking observed variability to possible non-Keplerian disc components and testing thermo-chemical models.

Findings

Line shapes and FWHM differ between epochs.

ProDiMo model reproduces some line features but overpredicts FWHM.

Variability may be caused by disc winds or episodic accretion.

Abstract

We present for the first time a direct comparison of multi-epoch (2001-2002 and 2012) CO ro-vibrational emission lines from HD163296. We find that both the line shapes and the FWHM (Full Width Half Maximum) differ between these two epochs. The FWHM of the median observed line profiles are 10-25 km/s larger in the earlier epoch, and confirmed double peaks are only present in high J lines from 2001-2002. The line wings of individual transitions are similar in the two epochs making an additional central component in the later epoch a likely explanation for the single peaks and the lower FWHM. Variations in NIR brightness have been reported and could be linked to the observed variations. Additionally, we use the thermo chemical disc code ProDiMo to compare for the first time the line shapes, peak separations, FWHM, and line fluxes, to those observed. The ProDiMo model reproduces the peak separations, and low and mid J line fluxes well. The FWHM however, are over predicted and high J line fluxes are under predicted. We propose that a variable non-Keplerian component of the CO ro-vibrational emission, such as a disc wind or an episodic accretion funnel, is causing the difference between the two data sets collected at different epochs, and between model and observations. Additional CO ro-vibrational line detections (with CRIRES/VLT or NIRSPEC/Keck) or [Ne II] line observations with VISIR/VLT could help to clarify the cause of the variability.