The effects of rotation on massive star spectroscopic observables

Abstract

Rotation is ubiquitous among massive stars. With rotation comes a deformation to the surface geometry, which in turn leads to alterations in the distribution of parameters across the surface including surface gravity, temperature and ionization balance of surface elements. Often, these 3D effects are neglected when analyzing spectra of rapidly rotating massive stars. We aim to determine whether neglecting the 3D deformations resulting from rapid rotation has an impact on the final spectroscopic observables, and if so to what degree. Using the SPAMMS code, we generate a grid of synthetic spectra that account for the 3D geometry of rapidly rotating stars and compare them to synthetic spectra generated assuming spherical geometry. Using equivalent width and full width half maximum measurements as proxies, we determine how the measured temperature, helium abundance and projected rotation rates of individual lines in different ionization states vary with rotation rate and inclination. We find that the 3D geometry can have a significant impact on the measured parameters. We show that the temperature is highly dependent on both the rotation rate and the inclination, and that the same system viewed at different inclinations can have measured temperatures that differ by as much as 10\%. We also find that the helium abundance can be underestimated by as much as 60\%, and that lines in different ionization states can have measurable differences in rotation rates. We demonstrate that these differences in rotation rates can be seen in observed data and show that this could allow for an inclination independent measurement of the rotational velocity. Our results indicate that neglecting the 3D effects of rotation can cause significant biases in the measured spectroscopic parameters, and that in many cases, the measured values are more than 3$\sigma$ away from the true values.

Accepted for publication in A&A Letters; 6 pages (+2 appendix pages), 5 figures (+ 4 appendix figures)

References in corpus (11)

• Array Programming with NumPy
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• Pre-Supernova Evolution of Massive Single and Binary Stars
• ESPRESSO@VLT -- On-sky performance and first results
• Physics Of Eclipsing Binaries. II. Towards the Increased Model Fidelity
• Effects of gravitational darkening on the determination of fundamental parameters in fast rotating B-type stars
• The VLT-FLAMES survey of massive stars: rotation and nitrogen enrichment as the key to understanding massive star evolution
• The IACOB project: III. New observational clues to understand macroturbulent broadening in massive O- and B-type stars
• The young massive SMC cluster NGC 330 seen by MUSE. I. Observations and stellar content
• A census of OBe stars in nearby metal-poor dwarf galaxies reveals a high fraction of extreme rotators
• HST/COS Spectra of the Wind Lines of VFTS 102 and 285

Cited by in corpus (6)

• To Be or not to Be: the role of rotation in modeling Galactic Be X-ray Binaries
• The young massive SMC cluster NGC 330 seen by MUSE III. Stellar parameters and rotational velocities
• A low-metallicity massive contact binary undergoing slow Case A mass transfer: A detailed spectroscopic and orbital analysis of SSN 7 in NGC 346 in the SMC
• The IACOB project XIII. Helium enrichment in O-type stars as a tracer of past binary interaction
• The IACOB project XV. Updated calibrations of fundamental parameters of Galactic O-type stars
• Astrophysical parameters of LS 437 and the nature of X0726-260