Outbursts and stellar properties of the classical Be star HD 6226

TL;DR

This study comprehensively analyzes the outbursts, pulsations, and disk evolution of the classical Be star HD 6226 using multi-wavelength data, revealing links between pulsation modes and mass ejection mechanisms.

Contribution

It provides detailed spectroscopic and photometric analysis of HD 6226, establishing connections between pulsations and outbursts, and characterizing its disk dissipation timescales.

Findings

Star has spectral type B2.5IIIe with 74% critical rotation.

Outbursts linked to pulsation frequency differences.

Disk dissipation timescales similar to other Be stars.

Abstract

The bright and understudied classical Be star HD 6226 has exhibited multiple outbursts in the last several years during which the star grew a viscous decretion disk. We analyze 659 optical spectra of the system collected from 2017-2020, along with a UV spectrum from the Hubble Space Telescope and high cadence photometry from both TESS and the KELT survey. We find that the star has a spectral type of B2.5IIIe, with a rotation rate of 74% of critical. The star is nearly pole-on with an inclination of $13.4$ degree. We confirm the spectroscopic pulsational properties previously reported, and report on three photometric oscillations from KELT photometry. The outbursting behavior is studied with equivalent width measurements of H$\alpha$ and H$\beta$, and the variations in both of these can be quantitatively explained with two frequencies through a Fourier analysis. One of the frequencies for the emission outbursts is equal to the difference between two photometric oscillations, linking these pulsation modes to the mass ejection mechanism for some outbursts. During the TESS observation time period of 2019 October 7 to 2019 November 2, the star was building a disk. With a large dataset of H$\alpha$ and H$\beta$ spectroscopy, we are able to determine the timescales of dissipation in both of these lines, similar to past work on Be stars that has been done with optical photometry. HD 6226 is an ideal target with which to study the Be disk-evolution given its apparent periodic nature, allowing for targeted observations with other facilities in the future.