scholarly journals On the geometry and environment of repeating FRBs

2020 ◽  
Vol 500 (4) ◽  
pp. 4678-4684
Author(s):  
Shuang Du ◽  
Weihua Wang ◽  
Xuhao Wu ◽  
Renxin Xu
Keyword(s):  
Orbital Motion ◽  
Massive Stars ◽  
Asteroid Belt ◽  
Radio Bursts ◽  
Impact Model ◽  
Star Forming ◽  
Binary Separation ◽  
Companion Systems ◽  
Binary Separations ◽  
Geometrical Explanation

ABSTRACT We propose a geometrical explanation for periodically and non-periodically repeating fast radio bursts (FRBs) under neutron star (NS)–companion systems. We suggest a constant critical binary separation, rc, within which the interaction between the NS and companion can trigger FRBs. For an elliptic orbit with the minimum and maximum binary separations, rmin and rmax, a periodically repeating FRB with an active period could be reproduced if rmin < rc < rmax. However, if rmax < rc, the modulation of orbital motion will not work due to persistent interaction, and this kind of repeating FRBs should be non-periodic. We test relevant NS–companion binary scenarios on the basis of FRB 180916.J0158+65 and FRB 121102 under this geometrical frame. It is found that the pulsar–asteroid belt impact model is more suitable to explain these two FRBs since this model is compatible with different companions (e.g. massive stars and black holes). At last, we point out that FRB 121102-like samples are potential objects that can reveal the evolution of star-forming region.

scholarly journals The Circumstellar Environment of Embedded Massive Stars

2002 ◽  
Vol 12 ◽  
pp. 143-145 ◽  
Author(s):  
Lee G. Mundy ◽  
Friedrich Wyrowski ◽  
Sarah Watt
Keyword(s):  
Massive Star ◽  
Massive Stars ◽  
Low Mass Stars ◽  
Submillimeter Wavelength ◽  
Star Forming ◽  
Star Forming Regions ◽  
Low Mass ◽  
Circumstellar Environments ◽  
Near Future

Millimeter and submillimeter wavelength images of massive star-forming regions are uncovering the natal material distribution and revealing the complexities of their circumstellar environments on size scales from parsecs to 100’s of AU. Progress in these areas has been slower than for low-mass stars because massive stars are more distant, and because they are gregarious siblings with different evolutionary stages that can co-exist even within a core. Nevertheless, observational goals for the near future include the characterization of an early evolutionary sequence for massive stars, determination if the accretion process and formation sequence for massive stars is similar to that of low-mass stars, and understanding of the role of triggering events in massive star formation.

scholarly journals Populations of OB-type stars in galaxies

2010 ◽  
Vol 6 (S272) ◽  
pp. 233-241
Author(s):  
Christopher J. Evans
Keyword(s):  
Stellar Evolution ◽  
Massive Stars ◽  
Spectral Synthesis ◽  
High Redshift ◽  
Young Star ◽  
Magellanic Clouds ◽  
Star Forming ◽  
The Galaxy ◽  
External Galaxies

AbstractOne of the challenges for stellar astrophysics is to reach the point at which we can undertake reliable spectral synthesis of unresolved populations in young, star-forming galaxies at high redshift. Here I summarise recent studies of massive stars in the Galaxy and Magellanic Clouds, which span a range of metallicities commensurate with those in high-redshift systems, thus providing an excellent laboratory in which to study the role of environment on stellar evolution. I also give an overview of observations of luminous supergiants in external galaxies out to a remarkable 6.7 Mpc, in which we can exploit our understanding of stellar evolution to study the chemistry and dynamics of the host systems.

scholarly journals Formation of Orion fingers

2020 ◽  
Vol 495 (1) ◽  
pp. 1172-1187
Author(s):  
Ross Dempsey ◽  
Nadia L Zakamska ◽  
James E Owen
Keyword(s):  
Physical Properties ◽  
Time Scales ◽  
High Velocity ◽  
Massive Stars ◽  
Hydrodynamic Instabilities ◽  
Similar Time ◽  
Dynamical Interaction ◽  
Star Forming ◽  
Common System ◽  
Bow Shocks

ABSTRACT ‘Orion fingers’ are a system of dozens of bow shocks, with the wings of shocks pointing to a common system of origin, which is centred on a dynamically disintegrating system of several massive stars. The shock heads propagate with velocities of up to 300–400 km s−1, but the formation and physical properties of the ‘bullets’ leading the shocks are not known. Here, we summarize two possible scenarios for the formation of the ‘bullets’ and the resulting bow shocks (‘fingers’). In the first scenario, bullets are self-gravitating, Jupiter-mass objects that were formed rapidly and then ejected during the strong dynamical interactions of massive stars and their discs. This scenario naturally explains the similar time-scales for the outflow of bullets and for the dynamical interaction of the massive stars, but has some difficulty explaining the observed high velocities of the bullets. In the second scenario, bullets are formed via hydrodynamic instabilities in a massive, infrared-driven wind, naturally explaining the high velocities and the morphology of outflow, but the bullets are not required to be self-gravitating. The processes that created the Orion fingers are likely not unique to this particular star-forming region and may result in free-floating, high-velocity, core-less planets.

scholarly journals Star cluster formation and cloud dispersal by radiative feedback: dependence on metallicity and compactness

2020 ◽  
Vol 497 (3) ◽  
pp. 3830-3845 ◽  
Author(s):  
Hajime Fukushima ◽  
Hidenobu Yajima ◽  
Kazuyuki Sugimura ◽  
Takashi Hosokawa ◽  
Kazuyuki Omukai ◽  
...  
Keyword(s):  
Star Formation ◽  
Massive Stars ◽  
Cluster Formation ◽  
Star Clusters ◽  
Star Cluster ◽  
Star Forming ◽  
Dynamical Time ◽  
Low Metallicity ◽  
Higher Temperature ◽  
Dust Attenuation

ABSTRACT We study star cluster formation in various environments with different metallicities and column densities by performing a suite of 3D radiation hydrodynamics simulations. We find that the photoionization feedback from massive stars controls the star formation efficiency (SFE) in a star-forming cloud, and its impact sensitively depends on the gas metallicity Z and initial cloud surface density Σ. At Z = 1 Z⊙, SFE increases as a power law from 0.03 at Σ = 10 M⊙ pc−2 to 0.3 at $\Sigma = 300\,\mathrm{M}_{\odot }\, {\rm pc^{-2}}$. In low-metallicity cases $10^{-2}\!-\!10^{-1}\, \mathrm{Z}_{\odot }$, star clusters form from atomic warm gases because the molecule formation time is not short enough with respect to the cooling or dynamical time. In addition, the whole cloud is disrupted more easily by expanding H ii bubbles that have higher temperature owing to less efficient cooling. With smaller dust attenuation, the ionizing radiation feedback from nearby massive stars is stronger and terminate star formation in dense clumps. These effects result in inefficient star formation in low-metallicity environments: the SFE drops by a factor of ∼3 at Z = 10−2 Z⊙ compared to the results for Z = 1 Z⊙, regardless of Σ. Newborn star clusters are also gravitationally less bound. We further develop a new semi-analytical model that can reproduce the simulation results well, particularly the observed dependencies of the SFEs on the cloud surface densities and metallicities.

scholarly journals Extremely metal-poor galaxies with HST/COS: laboratories for models of low-metallicity massive stars and high-redshift galaxies

2019 ◽  
Vol 488 (3) ◽  
pp. 3492-3506 ◽  
Author(s):  
Peter Senchyna ◽  
Daniel P Stark ◽  
Jacopo Chevallard ◽  
Stéphane Charlot ◽  
Tucker Jones ◽  
...  
Keyword(s):  
Massive Stars ◽  
High Redshift ◽  
Formation Rate ◽  
Uv Spectra ◽  
High Redshift Galaxies ◽  
Star Forming ◽  
High Ionization ◽  
Moderate Resolution ◽  
Low Metallicity ◽  
Nearby Galaxies

Abstract Ultraviolet (UV) observations of local star-forming galaxies have begun to establish an empirical baseline for interpreting the rest-UV spectra of reionization-era galaxies. However, existing high-ionization emission line measurements at z > 6 ($\rm W_{C\, {\scriptscriptstyle IV},0}{} \gtrsim 20$ Å) are uniformly stronger than observed locally ($\rm W_{C\, {\scriptscriptstyle IV},0}{} \lesssim 2$ Å), likely due to the relatively high metallicities (Z/Z$\odot$ > 0.1) typically probed by UV surveys of nearby galaxies. We present new HST/COS spectra of six nearby (z < 0.01) extremely metal-poor galaxies (XMPs, Z/Z$\odot$ ≲ 0.1) targeted to address this limitation and provide constraints on the highly uncertain ionizing spectra powered by low-metallicity massive stars. Our data reveal a range of spectral features, including one of the most prominent nebular C iv doublets yet observed in local star-forming systems and strong He ii emission. Using all published UV observations of local XMPs to date, we find that nebular C iv emission is ubiquitous in very high specific star formation rate systems at low metallicity, but still find equivalent widths smaller than those measured in individual lensed systems at z > 6. Our moderate-resolution HST/COS data allow us to conduct an analysis of the stellar winds in a local nebular C iv emitter, which suggests that some of the tension with z > 6 data may be due to existing local samples not yet probing sufficiently high α/Fe abundance ratios. Our results indicate that C iv emission can play a crucial role in the JWST and ELT era by acting as an accessible signpost of very low metallicity (Z/Z$\odot$ < 0.1) massive stars in assembling reionization-era systems.

scholarly journals Analytic properties of the electromagnetic field of binary compact stars and electromagnetic precursors to gravitational waves

2020 ◽  
Vol 2020 (10) ◽  
Author(s):  
Tomoki Wada ◽  
Masaru Shibata ◽  
Kunihito Ioka
Keyword(s):  
Electromagnetic Field ◽  
Neutron Star ◽  
Gravitational Waves ◽  
Orbital Motion ◽  
Compact Stars ◽  
Close Binary ◽  
Radio Bursts ◽  
Poynting Flux ◽  
Electromagnetic Precursors ◽  
Spiral Arm

Abstract We analytically study the properties of the electromagnetic field in the vacuum around close binary compact stars containing at least one neutron star. We show that the orbital motion of the neutron star induces high multipole modes of the electromagnetic field just before the merger. These modes are superimposed to form a spiral arm configuration, and its edge is found to be a likely site for magnetic reconnection. These modes also enhance the total Poynting flux from neutron star binaries by a factor of 2–4. We also indicate that the electric field induced by the orbital motion leads to a magnetosphere around binaries and estimate its plasma density, which has a different parameter dependence than the Goldreich–Julian density. With these properties, we discuss possible electromagnetic counterparts to gravitational wave events, and identify radio precursors, such as fast radio bursts, as the most promising observational targets.

scholarly journals Fragmentation of a Protostellar Core: The Case of CB 230

2001 ◽  
Vol 200 ◽  
pp. 117-121 ◽  
Author(s):  
Ralf Launhardt
Keyword(s):  
Main Sequence ◽  
Angular Resolution ◽  
Continuum Emission ◽  
High Angular Resolution ◽  
Mass Star ◽  
Star Forming ◽  
Binary Separation ◽  
Molecular Outflow ◽  
Low Mass ◽  
Core Fragmentation

The Bok globule CB230 (L1177) contains an active, low-mass star-forming core which is associated with a double NIR reflection nebula, a collimated bipolar molecular outflow, and strong mm continuum emission. The morphology of the NIR nebula suggests the presence of a deeply embedded, wide binary protostellar system. High-angular resolution observations now reveal the presence of two sub-cores, two distinct outflow centers, and an embedded accretion disk associated with the western bipolar NIR nebula. Judging from the separation and specific angular momentum, the CB230 double protostar system probably results from core fragmentation and will end up at the upper end of the pre-main sequence binary separation distribution.

scholarly journals Massive Stars in the Tarantula Nebula: A Rosetta Stone for Extragalactic Supergiant HII Regions

Galaxies ◽  
2019 ◽  
Vol 7 (4) ◽  
pp. 88 ◽  
Author(s):  
Paul A. Crowther
Keyword(s):  
Massive Stars ◽  
Hii Regions ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
High Mass ◽  
Stellar Content ◽  
X Ray ◽  
Star Forming ◽  
Rosetta Stone ◽  
The Individual

A review of the properties of the Tarantula Nebula (30 Doradus) in the Large Magellanic Cloud is presented, primarily from the perspective of its massive star content. The proximity of the Tarantula and its accessibility to X-ray through radio observations permit it to serve as a Rosetta Stone amongst extragalactic supergiant HII regions since one can consider both its integrated characteristics and the individual properties of individual massive stars. Recent surveys of its high mass stellar content, notably the VLT FLAMES Tarantula Survey (VFTS), are reviewed, together with VLT/MUSE observations of the central ionizing region NGC 2070 and HST/STIS spectroscopy of the young dense cluster R136, provide a near complete Hertzsprung-Russell diagram of the region, and cumulative ionizing output. Several high mass binaries are highlighted, some of which have been identified from a recent X-ray survey. Brief comparisons with the stellar content of giant HII regions in the Milky Way (NGC 3372) and Small Magellanic Cloud (NGC 346) are also made, together with Green Pea galaxies and star forming knots in high-z galaxies. Finally, the prospect of studying massive stars in metal poor galaxies is evaluated.

scholarly journals Wiggling Structures Along the NGC 1333 IRAS 2A Outflow

2012 ◽  
Vol 8 (S292) ◽  
pp. 60-60
Author(s):  
Cheng-Hung Tsai ◽  
Huei-Ru Chen ◽  
Chin-Fei Lee ◽  
Naomi Hirano ◽  
Hsien Shang
Keyword(s):  
Binary System ◽  
Accretion Disk ◽  
Mirror Symmetry ◽  
Large Scale ◽  
Angular Resolution ◽  
Orbital Motion ◽  
Lateral Displacement ◽  
Binary Separation ◽  
Bipolar Outflow ◽  
Small Separation

AbstractWiggling structures in a bipolar outflow may be attributed to orbital motion of a binary system or precession of an accretion disk perturbed by a companion. The shocked knots along the outflow axis display a morphology with either mirror symmetry due to the orbital motion or point symmetry resulted from disk precession. Using the Submillimeter Array (SMA), our CO (2-1) and SiO (5-4) observations show wiggling structures in the collimated bipolar outflow driven by the NGC 1333 IRAS 2A Class 0 protostar (d ~ 200 pc). By fitting the peak positions of emission knots, we can examine the lateral displacement of the molecular jet to constrain parameters of the unresolved binary system, such as the binary separation and total binary mass. With an angular resolution of ~3″, we have determined the knot positions in SiO (5–4)(Fig. 1) and CO (2–1). As a first attempt, we consider the scenario of orbital motion in a binary system and estimate a total binary mass of ~ 1M⊙ and a binary separation of roughly ~ 20 AU, corresponding to ~ 0.1″. Such a small separation makes it challenging to resolve this hypothesized proto-binary system, which is thought to be responsible for the large-scale quadrupolar outflow nearly perpendicular with each other in CO (1–0).

scholarly journals A multifrequency study of the active star forming region NGC 6357

2006 ◽  
Vol 2 (S237) ◽  
pp. 400-400
Author(s):  
C. E. Cappa ◽  
R. H. Barbá ◽  
M. Arnal ◽  
N. Duronea ◽  
E. Fernández Lajús ◽  
...  
Keyword(s):  
Angular Resolution ◽  
Massive Stars ◽  
Radio Continuum ◽  
Large Array ◽  
Schmidt Telescope ◽  
Ionized Gas ◽  
Very Large Array ◽  
Active Star ◽  
Star Forming ◽  
Spiral Arm

To investigate the interaction of the massive stars with the gas and dust in the active star forming region NGC 6357, located in the Sagittarius spiral arm at a distance of 1.7-2.6 kpc (Massey et al. 2001), we analyzed the distribution of the neutral and ionized gas, and that of the dust, based on Hα, [OIII] and [SII] images obtained with the Curtis-Schmidt telescope at CTIO, radio continuum observations at 1.465 MHz obtained with the Very Large Array (NRAO) in the DnC configuration (synthesized beam = 38″), Hi data from the Parkes survey (angular resolution = 15′), CO(1-0) observations obtained with the Nanten radiotelescope at Las Campanas Observatory (angular resolution = 2.7′), and IR images in the four MSX bands (angular resolution = 18.3″).

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