A Be star with a low nitrogen abundance in the SMC cluster NGC330

Abstract

High-resolution UVES/VLT spectra of B12, an extreme pole-on Be star in the SMC cluster NGC330, have been analysed using non-LTE model atmospheres to obtain its chemical composition relative to the SMC standard star AV304. We find a general underabundance of metals which can be understood in terms of an extra contribution to the stellar continuum due to emission from a disk which we estimate to be at the ~25% level. When this is corrected for, the nitrogen abundance for B12 shows no evidence of enhancement by rotational mixing as has been found in other non-Be B-type stars in NGC330, and is inconsistent with evolutionary models which include the effects of rotational mixing. A second Be star, NGC330-B17, is also shown to have no detectable nitrogen lines. Possible explanations for the lack of rotational mixing in these rapidly rotating stars are discussed, one promising solution being the possibility that magnetic fields might inhibit rotational mixing.

7 pages, 4 figures. Submitted to A&A

References in corpus (13)

• Stellar evolution with rotation X: Wolf-Rayet star populations at solar metallicity
• Presupernova Evolution of Rotating Massive Stars II: -- Evolution of the Surface Properties
• Stellar evolution with rotation VII: Low metallicity models and the blue to red supergiant ratio in the SMC
• Be-star rotation: how close to critical?
• Quantitative Spectroscopy of O Stars at Low Metallicity. O Dwarfs in NGC 346
• A-type Supergiant Abundances in the SMC: Probes of Evolution
• Stellar evolution with rotation and magnetic fields II: General equations for the transport by Tayler--Spruit dynamo
• Understanding B-type Supergiants in the Low Metallicity Environment of the SMC
• Magnetic Fields in Massive Stars. II. The Buoyant Rise of Magnetic Flux Tubes Through the Radiative Interior
• B-type Supergiants in the SMC: Chemical compositions and comparison of static and unified models
• X-ray Modeling of Very Young Early Type Stars in the Orion Trapezium: Signatures of Magnetically Confined Plasmas and Evolutionary Implications
• More nitrogen rich B-type stars in the SMC cluster, NGC 330
• A non-LTE analysis of the spectra of two narrow lined main sequence stars in the SMC

Cited by in corpus (14)

• The VLT-FLAMES survey of massive stars: atmospheric parameters and rotational velocity distributions for B-type stars in the Magellanic Clouds
• Properties of OB star-black hole systems derived from detailed binary evolution models
• The VLT-FLAMES Tarantula Survey XIX. B-type Supergiants - Atmospheric parameters and nitrogen abundances to investigate the role of binarity and the width of the main sequence
• The ARAUCARIA project: Grid-Based Quantitative Spectroscopic Study of Massive Blue Stars in NGC55
• The Single Star Path to Be Stars
• The VLT-FLAMES Tarantula Survey. XXX. Red stragglers in the clusters Hodge 301 and SL 639
• The effects of stellar rotation along the main sequence of the 100 Myr old massive cluster NGC 1850
• The Araucaria Project: VLT-spectroscopy of blue massive stars in NGC 55
• The VLT-FLAMES survey of massive stars: Nitrogen abundances for Be-type stars in the Magellanic Clouds
• The VLT-FLAMES Tarantula Survey: XXVIII. Nitrogen abundances for apparently single dwarf and giant B-type stars with small projected rotational velocities
• Rotational Mixing in Be Stars: Nitrogen Abundances for a Sample of Be Stars from the MiMeS Survey
• Boron depletion in Galactic early B-type stars reveals two different main sequence star populations
• Non-LTE Equivalent Widths for NII with Error Estimates
• A stringent upper limit on Be star fractions produced by binary interaction