Stellar population of the superbubble N 206 in the LMC

Context. Clusters or associations of early-type stars are often associated with a “superbubble” of hot gas. The formation of such superbubbles is caused by the feedback from massive stars. The complex N 206 in the Large Magellanic Cloud (LMC) exhibits a superbubble and a rich massive star population. Aims. Our goal is to perform quantitative spectral analyses of all massive stars associated with the N 206 superbubble in order to determine their stellar and wind parameters. We compare the superbubble energy budget to the stellar energy input and discuss the star formation history of the region. Methods. We observed the massive stars in the N 206 complex using the multi-object spectrograph FLAMES at ESO’s Very Large Telescope (VLT). Available ultra-violet (UV) spectra from archives are also used. The spectral analysis is performed with Potsdam Wolf–Rayet (PoWR) model atmospheres by reproducing the observations with the synthetic spectra. Results. We present the stellar and wind parameters of the OB stars and the two Wolf–Rayet (WR) binaries in the N 206 complex. Twelve percent of the sample show Oe/Be type emission lines, although most of them appear to rotate far below critical. We found eight runaway stars based on their radial velocity. The wind-momentum luminosity relation of our OB sample is consistent with the expectations. The Hertzsprung–Russell diagram (HRD) of the OB stars reveals a large age spread (1–30 Myr), suggesting different episodes of star formation in the complex. The youngest stars are concentrated in the inner part of the complex, while the older OB stars are scattered over outer regions. We derived the present day mass function for the entire N 206 complex as well as for the cluster NGC 2018. The total ionizing photon flux produced by all massive stars in the N 206 complex is Q0 ≈ 5 × 1050 s−1, and the mechanical luminosity of their stellar winds amounts to Lmec = 1.7 × 1038 erg s−1. Three very massive Of stars are found to dominate the feedback among 164 OB stars in the sample. The two WR winds alone release about as much mechanical luminosity as the whole OB star sample. The cumulative mechanical feedback from all massive stellar winds is comparable to the combined mechanical energy of the supernova explosions that likely occurred in the complex. Accounting also for the WR wind and supernovae, the mechanical input over the last five Myr is ≈ 2.3 × 1052 erg. Conclusions. The N206 complex in the LMC has undergone star formation episodes since more than 30 Myr ago. From the spectral analyses of its massive star population, we derive a current star formation rate of 2.2 × 10−3 M⊙ yr−1. From the combined input of mechanical energy from all stellar winds, only a minor fraction is emitted in the form of X-rays. The corresponding input accumulated over a long time also exceeds the current energy content of the complex by more than a factor of five. The morphology of the complex suggests a leakage of hot gas from the superbubble.

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Metallicity studies of the Galactic center: evidence for a top-heavy star formation history?

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314000696 ◽

2013 ◽

Vol 9 (S303) ◽

pp. 252-253

Author(s):

Francisco Najarro ◽

Diego de la Fuente ◽

Tom R. Geballe ◽

Don F. Figer

Keyword(s):

Star Formation ◽

Massive Star ◽

Local Group ◽

Galactic Center ◽

Massive Stars ◽

Star Formation History ◽

Test Bed ◽

Formation History ◽

History Of ◽

Stellar Properties

AbstractThe Galactic center (GC) region hosts three of the most massive resolved young clusters in the Local Group and constitutes a test bed for studying the star formation history of the region and inferring the possibility of a top-heavy scenario. Further, recent detection of a large number of apparently isolated massive stars within the inner 80 pc of the Galactic center has raised fundamental questions regarding massive star formation in a such a dense and harsh environment. Noting that most of the isolated massive stars have spectral analogs in the Quintuplet cluster, we have undertaken a combined analysis of the infrared spectra of both selected Quintuplet stars and the isolated objects using Gemini spectroscopy. We present preliminary results, aiming at α-elements versus iron abundances, stellar properties, ages and radial velocities which will differentiate the top-heavy and star-formation scenarios.

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Surround and Squash: the impact of superbubbles on the interstellar medium in Scorpius–Centaurus OB2

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732416 ◽

2018 ◽

Vol 619 ◽

pp. A120 ◽

Cited By ~ 16

Author(s):

Martin G. H. Krause ◽

Andreas Burkert ◽

Roland Diehl ◽

Katharina Fierlinger ◽

Benjamin Gaczkowski ◽

...

Keyword(s):

Star Formation ◽

Interstellar Medium ◽

Massive Star ◽

Massive Stars ◽

Three Dimensional ◽

X Rays ◽

Hot Gas ◽

Sky Survey ◽

Hydrodynamical Simulations ◽

The Impact

Context. Feedback by massive stars shapes the interstellar medium and is thought to influence subsequent star formation. The details of this process are under debate. Aims. We exploited observational constraints on stars, gas, and nucleosynthesis ashes for the closest region with recent massive-star formation, Scorpius–Centaurus OB2, and combined them with three-dimensional (3D) hydrodynamical simulations in order to address the physics and history of the Scorpius–Centaurus superbubble. Methods. We used published cold gas observations of continuum and molecular lines from Planck, Herschel, and APEX. We analysed the Galactic All Sky Survey (GASS) to investigate shell structures in atomic hydrogen, and used Hipparcos and Gaia data in combination with interstellar absorption against stars to obtain new constraints for the distance to the Hi features. Hot gas is traced in soft X-rays via the ROSAT all sky survey. Nucleosynthesis ejecta from massive stars were traced with new INTEGRAL spectrometer observations via 26Al radioactivity. We also performed 3D hydrodynamical simulations for the Sco–Cen superbubble. Results. Soft X-rays and a now more significant detection of 26Al confirm recent (≈1 Myr ago) input of mass, energy, and nucleosynthesis ejecta, likely from a supernova in the Upper Scorpius (USco) subgroup. We confirm a large supershell around the entire OB association and perform a 3D hydrodynamics simulation with a conservative massive star population that reproduces the morphology of the superbubble. High-resolution GASS observations reveal a nested, filamentary supershell. The filaments are possibly related to the Vishniac clumping instability, but molecular gas (Lupus I) is only present where the shell coincides with the connecting line between the subgroups of the OB association, suggesting a connection to the cloud, probably an elongated sheet, out of which the OB association formed. Stars have formed sequentially in the subgroups of the OB association and currently form in Lupus I. To investigate the impact of massive star feedback on extended clouds, we simulate the interaction of a turbulent cloud with the hot, pressurised gas in a superbubble. The hot gas fills the tenuous regions of the cloud and compresses the denser parts. Stars formed in these dense clumps would have distinct spatial and kinematic distributions. Conclusions. The combined results from observations and simulations are consistent with a scenario where dense gas was initially distributed in a band elongated in the direction now occupied by the OB association. Superbubbles powered by massive stars would then repeatedly break out of the elongated parent cloud, and surround and squash the denser parts of the gas sheet and thus induce more star formation. The expected spatial and kinematic distribution of stars is consistent with observations of Sco–Cen. The scenario might apply to many similar regions in the Galaxy and also to active galactic nucleus (AGN)-related superbubbles.

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Massive Star Formation in the Sparsest Environments

Proceedings of the International Astronomical Union ◽

10.1017/s174392131600822x ◽

2015 ◽

Vol 11 (S315) ◽

Author(s):

Sally Oey ◽

Joel B. Lamb

Keyword(s):

Star Formation ◽

Massive Star ◽

Massive Stars ◽

Hii Regions ◽

Magellanic Cloud ◽

Small Magellanic Cloud ◽

Massive Star Formation ◽

Ob Stars ◽

Runaway Stars

AbstractThere is growing evidence that massive stars sometimes form in extremely sparse environments. The RIOTS4 survey presents a variety of evidence supporting this scenario, including a sample of 14 OB stars in the Small Magellanic Cloud (SMC) that appear to have formed in situ as field stars. This is based on the presence of dense, symmetric HII regions hosting apparent non-runaway stars. We also present a spatially complete IMF of SMC field OB stars for masses > 7 M⊙, showing that the slope is much steeper than the Salpeter value. The binary fraction among field OB stars is also the same as in clusters, based on a RIOTS4 subsample. These results suggest a relative, but incomplete, suppression of massive star formation in the sparsest regimes.

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Gamma-ray bursts: the most powerful cosmic explosions

Symposium - International Astronomical Union ◽

10.1017/s0074180900211704 ◽

2003 ◽

Vol 212 ◽

pp. 106-114

Author(s):

Lex Kaper

Keyword(s):

Star Formation ◽

Massive Star ◽

Gamma Ray ◽

Massive Stars ◽

Star Formation History ◽

Host Galaxies ◽

Star Forming ◽

Binary Neutron Star ◽

Blue Galaxies ◽

Cosmic Explosions

With the detection of gamma-ray burst (GRB) afterglows, the cosmological origin of GRBs has been firmly established. Recent observations suggest that (long-duration) GRBs are due to the collapse of a massive star forming a black hole. Besides theoretical arguments, observational evidence supporting this hypothesis comes from the coincidence of several GRBs with a supernova. Also, all accurately located GRBs are contained in the optical (restframe UV) extent of distant, blue galaxies. Some of these host galaxies show relatively high star-formation rates, which is expected when massive stars and GRBs are physically linked. Alternatively, GRBs can be produced by the merging of a binary neutron star system, such as the Hulse-Taylor binary pulsar. Very likely GRBs trace the massive-star populations in distant galaxies. With their enormous brightness, GRBs are powerful probes of the early universe, providing information on the properties of their host galaxies, the cosmic star-formation history, and potentially the first generations of massive stars.

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Testing massive star evolution, star formation history, and feedback at low metallicity

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935365 ◽

2019 ◽

Vol 625 ◽

pp. A104 ◽

Cited By ~ 18

Author(s):

V. Ramachandran ◽

W.-R. Hamann ◽

L. M. Oskinova ◽

J. S. Gallagher ◽

R. Hainich ◽

...

Keyword(s):

Black Holes ◽

Star Formation ◽

Large Scale ◽

Massive Star ◽

Main Sequence ◽

Massive Stars ◽

Star Formation History ◽

Core Collapse ◽

Single Star ◽

Stellar Feedback

Stars that start their lives with spectral types O and early B are the progenitors of core-collapse supernovae, long gamma-ray bursts, neutron stars, and black holes. These massive stars are the primary sources of stellar feedback in star-forming galaxies. At low metallicities, the properties of massive stars and their evolution are not yet fully explored. Here we report a spectroscopic study of 320 massive stars of spectral types O (23 stars) and B (297 stars) in the Wing of the Small Magellanic Cloud (SMC). The spectra, which we obtained with the ESO Very Large Telescope, were analyzed using state-of-the-art stellar atmosphere models, and the stellar parameters were determined. We find that the stellar winds of our sample stars are generally much weaker than theoretically expected. The stellar rotation rates show broad, tentatively bimodal distributions. The upper Hertzsprung–Russell diagram (HRD) is well populated by the stars of our sample from a specific field in the SMC Wing. A few very luminous O stars are found close to the main sequence, while all other, slightly evolved stars obey a strict luminosity limit. Considering additional massive stars in evolved stages, with published parameters and located all over the SMC, essentially confirms this picture. The comparison with single-star evolutionary tracks suggests a dichotomy in the fate of massive stars in the SMC. Only stars with an initial mass below ∼30 M⊙ seem to evolve from the main sequence to the cool side of the HRD to become a red supergiant and to explode as type II-P supernova. In contrast, stars with initially more than ∼30 M⊙ appear to stay always hot and might evolve quasi chemically homogeneously, finally collapsing to relatively massive black holes. However, we find no indication that chemical mixing is correlated with rapid rotation. We measured the key parameters of stellar feedback and established the links between the rates of star formation and supernovae. Our study demonstrates that in metal-poor environments stellar feedback is dominated by core-collapse supernovae in combination with winds and ionizing radiation supplied by a few of the most massive stars. We found indications of the stochastic mode of massive star formation, where the resulting stellar population is fully capable of producing large-scale structures such as the supergiant shell SMC-SGS 1 in the Wing. The low level of feedback in metal-poor stellar populations allows star formation episodes to persist over long timescales.

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The Formation of Massive Stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311000184 ◽

2010 ◽

Vol 6 (S270) ◽

pp. 57-64

Author(s):

Ian A. Bonnell ◽

Rowan J Smith

Keyword(s):

Star Formation ◽

Magnetic Fields ◽

Massive Star ◽

Massive Stars ◽

Cluster Formation ◽

High Mass ◽

Prestellar Cores ◽

Stellar Mergers ◽

Massive Clusters ◽

Viable Mechanism

AbstractThere has been considerable progress in our understanding of how massive stars form but still much confusion as to why they form. Recent work from several sources has shown that the formation of massive stars through disc accretion, possibly aided by gravitational and Rayleigh-Taylor instabilities is a viable mechanism. Stellar mergers, on the other hand, are unlikely to occur in any but the most massive clusters and hence should not be a primary avenue for massive star formation. In contrast to this success, we are still uncertain as to how the mass that forms a massive star is accumulated. there are two possible mechanisms including the collapse of massive prestellar cores and competitive accretion in clusters. At present, there are theoretical and observational question marks as to the existence of high-mass prestellar cores. theoretically, such objects should fragment before they can attain a relaxed, centrally condensed and high-mass state necessary to form massive stars. Numerical simulations including cluster formation, feedback and magnetic fields have not found such objects but instead point to the continued accretion in a cluster potential as the primary mechanism to form high-mass stars. Feedback and magnetic fields act to slow the star formation process and will reduce the efficiencies from a purely dynamical collapse but otherwise appear to not significantly alter the process.

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Bimodal regime in young massive clusters leading to subsequent stellar generations

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315009023 ◽

2015 ◽

Vol 12 (S316) ◽

pp. 294-301

Author(s):

Richard Wünsch ◽

Jan Palouš ◽

Guillermo Tenorio-Tagle ◽

Casiana Muñoz-Tuñón ◽

Soňa Ehlerová

Keyword(s):

Stellar Evolution ◽

Column Density ◽

First Generation ◽

Massive Stars ◽

Ionising Radiation ◽

Cluster Center ◽

Stellar Winds ◽

Hot Gas ◽

Massive Clusters ◽

By Products

AbstractMassive stars in young massive clusters insert tremendous amounts of mass and energy into their surroundings in the form of stellar winds and supernova ejecta. Mutual shock-shock collisions lead to formation of hot gas, filling the volume of the cluster. The pressure of this gas then drives a powerful cluster wind. However, it has been shown that if the cluster is massive and dense enough, it can evolve in the so–called bimodal regime, in which the hot gas inside the cluster becomes thermally unstable and forms dense clumps which are trapped inside the cluster by its gravity. We will review works on the bimodal regime and discuss the implications for the formation of subsequent stellar generations. The mass accumulates inside the cluster and as soon as a high enough column density is reached, the interior of the clumps becomes self-shielded against the ionising radiation of stars and the clumps collapse and form new stars. The second stellar generation will be enriched by products of stellar evolution from the first generation, and will be concentrated near the cluster center.

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DDO68-V1: an extremely metal-poor LBV in a void galaxy

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318006439 ◽

2018 ◽

Vol 14 (S344) ◽

pp. 392-395

Author(s):

Yulia Perepelitsyna ◽

Simon Pustilnik

Keyword(s):

Star Formation ◽

Massive Star ◽

Massive Stars ◽

Rare Event ◽

Local Universe ◽

Hii Region ◽

V Band ◽

Star Evolution ◽

Low Metallicity ◽

Massive Star Evolution

AbstractThe lowest metallicity massive stars in the Local Universe with $Z\sim \left( {{Z}_{\odot }}/50-{{Z}_{\odot }}/30 \right)$ are the crucial objects to test the validity of assumptions in the modern models of very low-metallicity massive star evolution. These models, in turn, have major implications for our understanding of galaxy and massive star formation in the early epochs. DDO68-V1 in a void galaxy DDO68 is a unique extremely metal-poor massive star. Discovered by us in 2008 in the HII region Knot3 with $Z={{Z}_{\odot }}/35\,\left[ 12+\log \left( \text{O/H} \right)\sim 7.14 \right]$, DDO68-V1 was identified as an LBV star. We present here the LBV lightcurve in V band, combining own new data and the last archive and/or literature data on the light of Knot3 over the 30 years. We find that during the years 2008-2011 the LBV have experienced a very rare event of ‘giant eruption’ with V-band amplitude of 4.5 mag ($V\sim {{24.5}^{m}}-{{20}^{m}}$).

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Line-driven ablation of circumstellar discs – IV. The role of disc ablation in massive star formation and its contribution to the stellar upper mass limit

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/sty3394 ◽

2018 ◽

Vol 483 (4) ◽

pp. 4893-4900 ◽

Cited By ~ 3

Author(s):

Nathaniel Dylan Kee ◽

Rolf Kuiper

Keyword(s):

Star Formation ◽

Massive Star ◽

Loss Rate ◽

Massive Stars ◽

Mass Loss Rate ◽

Ablation Rate ◽

Massive Star Formation ◽

Future Studies ◽

Accretion Rates

Abstract Radiative feedback from luminous, massive stars during their formation is a key process in moderating accretion on to the stellar object. In the prior papers in this series, we showed that one form such feedback takes is UV line-driven disc ablation. Extending on this study, we now constrain the strength of this effect in the parameter range of star and disc properties appropriate to forming massive stars. Simulations show that ablation rate depends strongly on stellar parameters, but that this dependence can be parameterized as a nearly constant, fixed enhancement over the wind mass-loss rate, allowing us to predict the rate of disc ablation for massive (proto)stars as a function of stellar mass and metallicity. By comparing this to predicted accretion rates, we conclude that ablation is a strong feedback effect for very massive (proto)stars which should be considered in future studies of massive star formation.

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HII regions and star formation in the Magellanic Clouds

Symposium - International Astronomical Union ◽

10.1017/s0074180900200211 ◽

1991 ◽

Vol 148 ◽

pp. 139-144 ◽

Cited By ~ 2

Author(s):

Robert C. Kennicutt

Keyword(s):

Star Formation ◽

Interstellar Medium ◽

Massive Star ◽

Massive Stars ◽

Hii Regions ◽

Magellanic Clouds ◽

H Ii Regions ◽

Distant Galaxies ◽

Close Range ◽

Mass Functions

The H II regions in the Magellanic Clouds provide an opportunity to characterize the global star formation properties of a galaxy at close range. They also provide a unique laboratory for testing empirical tracers of the massive star formation rates and initial mass functions in more distant galaxies, and for studying the dynamical interactions between massive stars and the interstellar medium. This paper discusses several current studies in these areas.

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