scholarly journals The NGC 346 massive star census

2020 ◽  
Vol 634 ◽  
pp. A6 ◽  
Author(s):  
P. L. Dufton ◽  
C. J. Evans ◽  
D. J. Lennon ◽  
I. Hunter
Keyword(s):  
Magnetic Field ◽  
Massive Star ◽  
Main Sequence ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Evolutionary Models ◽  
Qualitative Comparison ◽  
Single Star ◽  
Early Type Stars ◽  
The Magnetic Field

Previous analyses of two large spectroscopic surveys of early-type stars in the Large Magellanic Cloud (LMC) have found an excess of nitrogen enriched B-type targets with a ve sin i ≤ 40 km s−1 compared with the predictions of single star evolutionary models that incorporate rotational mixing. By contrast, the number of such targets with 40 <  ve sin i ≤ 80 km s−1 was consistent with such models. We have undertaken a similar analysis for 61 B-type targets which lie towards the young cluster, NGC 346 in the Small Magellanic Cloud (SMC). These again have projected rotational velocities, ve sin i ≤ 80 km s−1, are not classified as supergiants, and are apparently single. Approximately 65% of these SMC targets could have nitrogen enhancements of less than 0.3 dex, which is consistent with them having experienced only small amounts of mixing due to their low rotational velocities. However, as with the previous LMC surveys, an excess of stars with low projected rotational velocities, ve sin i ≤ 40 km s−1, and significant nitrogen enrichments is found. This is estimated to be approximately 5% of the total population of apparently single B-type stars or 40% of all stars with current rotational velocities of less than 40 km s−1; these percentages are similar to those found previously for the two LMC samples. For all three surveys, the presence of undetected binaries and other uncertainties imply that these percentages might be underestimated and that it is indeed possible for all the single stars with current rotational velocities of less than 40 km s−1 to be nitrogen enriched. Two possible explanations incorporate the effects of the magnetic field, via either a stellar merger followed by magnetic braking or the evolution of a single star with a large magnetic field. Both mechanisms would appear to be compatible with the observed frequency of nitrogen-enriched stars in the Magellanic Clouds. Differences in the properties of the nitrogen-enriched stars compared with the remainder of the sample would be consistent with the former mechanism. For the latter, a qualitative comparison with Galactic evolutionary models that incorporate magnetic fields is encouraging in terms of the amount of nitrogen enrichment and its presence in stars near the zero-age main sequence.

scholarly journals The Physical Parameters of Four WC-type Wolf–Rayet Stars in the Large Magellanic Cloud: Evidence of Evolution*

2022 ◽  
Vol 924 (2) ◽  
pp. 44
Author(s):  
Erin Aadland ◽  
Philip Massey ◽  
D. John Hillier ◽  
Nidia Morrell
Keyword(s):  
Spectral Synthesis ◽  
Mass Loss Rate ◽  
Large Magellanic Cloud ◽  
Stellar Atmosphere ◽  
Magellanic Cloud ◽  
Physical Parameters ◽  
Evolutionary Models ◽  
Single Star ◽  
Oxygen Abundance ◽  
Solar Metallicity

Abstract We present a spectral analysis of four Large Magellanic Cloud (LMC) WC-type Wolf–Rayet (WR) stars (BAT99-8, BAT99-9, BAT99-11, and BAT99-52) to shed light on two evolutionary questions surrounding massive stars. The first is: are WO-type WR stars more oxygen enriched than WC-type stars, indicating further chemical evolution, or are the strong high-excitation oxygen lines in WO-type stars an indication of higher temperatures. This study will act as a baseline for answering the question of where WO-type stars fall in WR evolution. Each star’s spectrum, extending from 1100 to 25000 Å, was modeled using cmfgen to determine the star’s physical properties such as luminosity, mass-loss rate, and chemical abundances. The oxygen abundance is a key evolutionary diagnostic, and with higher resolution data and an improved stellar atmosphere code, we found the oxygen abundance to be up to a factor of 5 lower than that of previous studies. The second evolutionary question revolves around the formation of WR stars: do they evolve by themselves or is a close companion star necessary for their formation? Using our derived physical parameters, we compared our results to the Geneva single-star evolutionary models and the Binary Population and Spectral Synthesis (BPASS) binary evolutionary models. We found that both the Geneva solar-metallicity models and BPASS LMC-metallicity models are in agreement with the four WC-type stars, while the Geneva LMC-metallicity models are not. Therefore, these four WC4 stars could have been formed either via binary or single-star evolution.

scholarly journals Magnetic Fields in the Irregular Galaxy LMC

1993 ◽  
Vol 157 ◽  
pp. 317-319
Author(s):  
Richard Wielebinski
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Radio Continuum ◽  
The South ◽  
Irregular Galaxy ◽  
New Radio ◽  
The Magnetic Field

New radio continuum surveys allowed the determination of the magnetic field in the Large Magellanic Cloud. The magnetic field is filamentary, extending to the south of the 30 Doradus nebula. Some possible explanations for this unusual morphology are discussed.

scholarly journals The magnetic field structure of the Small Magellanic Cloud

2008 ◽  
Vol 4 (S256) ◽  
pp. 178-183 ◽  
Author(s):  
Antonio Mário Magalhães ◽  
Aiara Lobo Gomes ◽  
Aline de Almeida Vidotto ◽  
Cláudia Vilega Rodrigues ◽  
Antonio Pereyra ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Intensity ◽  
Magnetic Field Intensity ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Point Sources ◽  
Small Magellanic Cloud ◽  
Imaging Data ◽  
Polarization Data ◽  
The Magnetic Field

AbstractWe describe two studies of the interstellar magnetic field in regions of the Small Magellanic Cloud (SMC), including those affected by the interaction with the Large Magellanic Cloud (LMC). We use optical polarization data from aligned grains in the interstellar medium of the SMC in order to map the sky-projected direction of the magnetic field and determine characteristics of the SMC and Pan-Magellanic field structures. The earlier, photoelectric data are reanalyzed and they provide values for the average projected magnetic field intensity (1.7 × 10−6G) and the random field component intensity (3.5 × 10−6G). Another on-going program uses imaging data and, when concluded, will allow more local estimates of the field intensity in the SMC NE/Wing regions. Additional goals include cross-correlating our field mapping results with those of point sources and structures found by the Spitzer Space Telescope in the SMC between 3.6 and 8 μm.

scholarly journals The effects of surface fossil magnetic fields on massive star evolution: III. The case of τ Sco

2021 ◽  
Author(s):  
Z Keszthelyi ◽  
G Meynet ◽  
F Martins ◽  
A de Koter ◽  
A David-Uraz
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Massive Star ◽  
Slow Rotation ◽  
Single Star ◽  
Surface Magnetic Field ◽  
Fundamental Parameters ◽  
Chemical Enrichment ◽  
Star Models ◽  
Nitrogen Excess

Abstract τ Sco, a well-studied magnetic B-type star in the Uτer Sco association, has a number of surprising characteristics. It rotates very slowly and shows nitrogen excess. Its surface magnetic field is much more complex than a purely dipolar configuration which is unusual for a magnetic massive star. We employ the cmfgen radiative transfer code to determine the fundamental parameters and surface CNO and helium abundances. Then, we employ mesa and genec stellar evolution models accounting for the effects of surface magnetic fields. To reconcile τ Sco’s properties with single-star models, an increase is necessary in the efficiency of rotational mixing by a factor of 3 to 10 and in the efficiency of magnetic braking by a factor of 10. The spin down could be explained by assuming a magnetic field decay scenario. However, the simultaneous chemical enrichment challenges the single-star scenario. Previous works indeed suggested a stellar merger origin for τ Sco. However, the merger scenario also faces similar challenges as our magnetic single-star models to explain τ Sco’s simultaneous slow rotation and nitrogen excess. In conclusion, the single-star channel seems less likely and versatile to explain these discrepancies, while the merger scenario and other potential binary-evolution channels still require further assessment as to whether they may self-consistently explain the observables of τ Sco.

scholarly journals Modelling the photometric variability of magnetic massive stars with the Analytical Dynamical Magnetosphere model

2019 ◽  
Author(s):  
M S Munoz ◽  
G A Wade ◽  
Y Nazé ◽  
J Puls ◽  
S Bagnulo ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electron Scattering ◽  
Massive Star ◽  
Massive Stars ◽  
Mass Density ◽  
Magellanic Clouds ◽  
Light Curves ◽  
Photometric Variability ◽  
P Type ◽  
The Magnetic Field

Abstract In this paper, we investigate the photometric variability of magnetic O-type stars. Such stars possess oblique, predominantly dipolar magnetic fields that confine their winds roughly axisymmetrically about the magnetic equator, thus forming a magnetosphere. We interpret their photometric variability as phase-dependent magnetospheric occultations. For massive star winds dominated by electron scattering opacity in the optical and NIR, we can compute synthetic light curves from simply knowing the magnetosphere’s mass density distribution. We exploit the newly-developed Analytical Dynamical Magnetosphere model (ADM) in order to obtain the predicted circumstellar density structures of magnetic O-type stars. The simplicity in our light curve synthesis model allows us to readily conduct a parameter space study. For validation purposes, we first apply our algorithm to HD 191612, the prototypical Of?p star. Next, we attempt to model the photometric variability of the Of?p-type stars identified in the Magellanic Clouds using OGLE photometry. We evaluate the compatibility of the ADM predictions with the observed photometric variations, and discuss the magnetic field properties that are implied by our modelling.

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