Variability in the CO ro-vibrational lines from HD163296

Abstract

We present for the first time a direct comparison of multi-epoch (2001-2002 and 2012) CO ro-vibrational emission lines from HD 163296. We find that both the line shapes and the FWHM (full width at half-maximum) differ between these two epochs. The FWHM of the median observed line profiles are 10-25 km s(-1) larger in the earlier epoch, and confirmed double peaks are only present in high J lines from 2001 to 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 near-infrared 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 overpredicted and high J line fluxes are underpredicted. 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 cryogenic high-resolution infrared echelle spectrograph/Very Large Telescope (VLT) or Near InfraRed SPECtrometer/Keck) or [Ne ii] line observations with VLT Imager and Spectrometer for mid Infrared/VLT could help to clarify the cause of the variability.