The OVz stars in NGC 346: distribution, stellar parameters and insights into low-metallicity effects

Abstract

OVz stars are identified by their optical spectra, in which the He II 4686 absorption line is stronger than any other He line. This spectral characteristic suggests that these stars may be less luminous, less evolved, and located closer to the zero-age main sequence (ZAMS). Although their evolutionary status is still debated, OVz stars are key candidates for understanding the earliest stages of massive star evolution. In this study, we analyze OVz stars in the star-forming regions NGC 346 in the Small Magellanic Cloud (SMC) and 30 Doradus in the Large Magellanic Cloud (LMC), aiming to determine their physical properties and investigate the role of low metallicity in the emergence of the Vz peculiarity. We identified a sample of OVz and OV stars in NGC 346 using spectra obtained with the Magellan Echellette (MagE) spectrograph at Las Campanas Observatory. Spectral classification was based on the equivalent width ratios of key He lines. Quantitative spectroscopic analyses were carried out using the IACOB-BROAD and IACOB-GBAT/FASTWIND tools. For consistency, previously identified OV and OVz stars in 30 Doradus were reclassified following the same criteria.

arXiv commentAccepted for publication in A&A. 20 pages, 13 figures, 7 tables

References in corpus (31)

• Grids of stellar models with rotation - I. Models from 0.8 to 120 Msun at solar metallicity (Z = 0.014)
• Pre-Supernova Evolution of Massive Single and Binary Stars
• Rotating Massive Main-Sequence Stars I: Grids of Evolutionary Models and Isochrones
• Mass loss from hot massive stars
• The Galactic O-Star Spectroscopic Survey (GOSSS). II. Bright Southern Stars
• Atmospheric NLTE-Models for the Spectroscopic Analysis of Blue Stars with Winds. II. Line-Blanketed Models
• Quantitative Spectroscopy of O Stars at Low Metallicity. O Dwarfs in NGC 346
• The IACOB project: I. Rotational velocities in Northern Galactic O and early B-type stars revisited. The impact of other sources of line-broadening
• The VLT-FLAMES Survey of Massive Stars: Observations centered on the Magellanic Cloud clusters NGC 330, NGC 346, NGC 2004, and the N11 region
• The VLT-FLAMES Tarantula Survey XII. Rotational velocities of the single O-type stars
• The VLT-FLAMES survey of massive stars: Surface chemical compositions of B-type stars in the Magellanic Clouds
• The Physical Properties and Effective Temperature Scale of O-type Stars as a Function of Metallicity. II. Analysis of 20 More Magellanic Cloud Stars, and Results from the Complete Sample
• The MagE Spectrograph
• The VLT-FLAMES survey of massive stars: Mass loss and rotation of early-type stars in the SMC
• The VLT-FLAMES Tarantula Survey XVII. Physical and wind properties of massive stars at the top of the main sequence
• Fundamental parameters of Galactic luminous OB stars VI. Temperatures, masses and WLR of Cyg OB2 supergiants
• Spectral analysis of early-type stars using a genetic algorithm based fitting method
• The VLT-FLAMES Tarantula Survey III: A very massive star in apparent isolation from the massive cluster R136
• The VLT-FLAMES Tarantula Survey XIV. The O-Type Stellar Content of 30 Doradus
• The VLT-FLAMES Tarantula Survey. XXIX. Massive star formation in the local 30 Doradus starburst
• The IACOB project. V. Spectroscopic parameters of the O-type stars in the modern grid of standards for spectral classification
• The Massive Star Content of NGC 3603
• The VLT-FLAMES Tarantula Survey XXIV. Stellar properties of the O-type giants and supergiants in 30 Doradus
• X-Shooting ULLYSES: massive stars at low metallicity. I. Project Description
• Magnetic fields in massive stars, their winds, and their nebulae
• A census of massive stars in NGC 346. Stellar parameters and rotational velocities
• The IACOB project. VI. On the elusive detection of massive O-type stars close to the ZAMS
• Deep Chandra survey of the Small Magellanic Cloud. III. Formation efficiency of High-Mass X-ray binaries
• X-Shooting ULLYSES: Massive stars at low metallicity. III. Terminal wind speeds of ULLYSES massive stars
• Stellar wind properties of the nearly complete sample of O stars in the low metallicity young star cluster NGC346 in the SMC galaxy
• The IACOB project: II. On the scatter of O-dwarf spectral type -- effective temperature calibrations