The evolution of massive bipolar jets and the birth of H II regions

1986 ◽  
Vol 64 (4) ◽  
pp. 383-386 ◽  
Author(s):  
John Ballys
Keyword(s):  
Ionizing Radiation ◽  
Ultraviolet Radiation ◽  
Stellar Evolution ◽  
Main Sequence ◽  
Massive Stars ◽  
H Ii Regions ◽  
Neutral Wind ◽  
Final Phase ◽  
Molecular Outflows ◽  
Neutral Gas

Observations suggest that outflows of neutral gas are among the first visible signs of the birth of a new star. Stars destined to be of spectral type O or B on the main sequence eventually emit large quantities of ionizing ultraviolet radiation that produce H II regions. The powerful neutral wind associated with the bipolar outflow phase of pre-main-sequence stellar evolution produces cavities in the gas surrounding a newborn star and regulates the escape of ionizing radiation from the vicinity of the star. The birth and early evolution of H II regions is the final phase in the development of bipolar, molecular outflows surrounding massive stars.

scholarly journals On the turbulence driving mode of expanding H ii regions

2020 ◽  
Vol 493 (4) ◽  
pp. 4643-4656 ◽  
Author(s):  
Shyam H Menon ◽  
Christoph Federrath ◽  
Rolf Kuiper
Keyword(s):  
Star Formation ◽  
Ionizing Radiation ◽  
Massive Stars ◽  
Parameter Analysis ◽  
Ionization Front ◽  
H Ii Regions ◽  
Driving Mode ◽  
Neutral Gas ◽  
Natural Mixture ◽  
Hydrodynamical Simulations

Abstract We investigate the turbulence driving mode of ionizing radiation from massive stars on the surrounding interstellar medium. We run hydrodynamical simulations of a turbulent cloud impinged by a plane-parallel ionization front. We find that the ionizing radiation forms pillars of neutral gas reminiscent of those seen in observations. We quantify the driving mode of the turbulence in the neutral gas by calculating the driving parameter b, which is characterized by the relation $\sigma _s^2 = \ln ({1+b^2\mathcal {M}^2})$ between the variance of the logarithmic density contrast $\sigma _s^2$ [where s = ln (ρ/ρ0) with the gas density ρ and its average ρ0], and the turbulent Mach number $\mathcal {M}$. Previous works have shown that b ∼ 1/3 indicates solenoidal (divergence-free) driving and b ∼ 1 indicates compressive (curl-free) driving, with b ∼ 1 producing up to ten times higher star formation rates than b ∼ 1/3. The time variation of b in our study allows us to infer that ionizing radiation is inherently a compressive turbulence driving source, with a time-averaged b ∼ 0.76 ± 0.08. We also investigate the value of b of the pillars, where star formation is expected to occur, and find that the pillars are characterized by a natural mixture of both solenoidal and compressive turbulent modes (b ∼ 0.4) when they form, and later evolve into a more compressive turbulent state with b ∼ 0.5–0.6. A virial parameter analysis of the pillar regions supports this conclusion. This indicates that ionizing radiation from massive stars may be able to trigger star formation by producing predominately compressive turbulent gas in the pillars.

scholarly journals Stellar models and isochrones from low-mass to massive stars including pre-main sequence phase with accretion

2019 ◽  
Vol 624 ◽  
pp. A137 ◽  
Author(s):  
L. Haemmerlé ◽  
P. Eggenberger ◽  
S. Ekström ◽  
C. Georgy ◽  
G. Meynet ◽  
...  
Keyword(s):  
Star Formation ◽  
Stellar Evolution ◽  
Main Sequence ◽  
Massive Stars ◽  
Mass Range ◽  
Stellar Clusters ◽  
Solar Metallicity ◽  
Low Mass ◽  
Stellar Models ◽  
Young Clusters

Grids of stellar models are useful tools to derive the properties of stellar clusters, in particular young clusters hosting massive stars, and to provide information on the star formation process in various mass ranges. Because of their short evolutionary timescale, massive stars end their life while their low-mass siblings are still on the pre-main sequence (pre-MS) phase. Thus the study of young clusters requires consistent consideration of all the phases of stellar evolution. But despite the large number of grids that are available in the literature, a grid accounting for the evolution from the pre-MS accretion phase to the post-MS phase in the whole stellar mass range is still lacking. We build a grid of stellar models at solar metallicity with masses from 0.8 M⊙ to 120 M⊙, including pre-MS phase with accretion. We use the GENEC code to run stellar models on this mass range. The accretion law is chosen to match the observations of pre-MS objects on the Hertzsprung-Russell diagram. We describe the evolutionary tracks and isochrones of our models. The grid is connected to previous MS and post-MS grids computed with the same numerical method and physical assumptions, which provides the widest grid in mass and age to date.

scholarly journals On monolithic supermassive stars

2020 ◽  
Vol 494 (2) ◽  
pp. 2236-2243 ◽  
Author(s):  
Tyrone E Woods ◽  
Alexander Heger ◽  
Lionel Haemmerlé
Keyword(s):  
Early Universe ◽  
Stellar Evolution ◽  
Time Scale ◽  
Main Sequence ◽  
Massive Stars ◽  
Rotating Stars ◽  
One Dimensional ◽  
General Relativistic ◽  
The One ◽  
Limiting Case

ABSTRACT Supermassive stars have been proposed as the progenitors of the massive ($\sim \!10^{9}\, \mathrm{M}_{\odot }$) quasars observed at z ∼ 7. Prospects for directly detecting supermassive stars with next-generation facilities depend critically on their intrinsic lifetimes, as well as their formation rates. We use the one-dimensional stellar evolution code kepler to explore the theoretical limiting case of zero-metallicity non-rotating stars, formed monolithically with initial masses between $10$ and $190\, \mathrm{kM}_{\odot }$. We find that stars born with masses between $\sim\! 60$ and $\sim\! 150\, \mathrm{kM}_{\odot }$ collapse at the end of the main sequence, burning stably for $\sim\! 1.5\, \mathrm{Myr}$. More massive stars collapse directly through the general relativistic instability after only a thermal time-scale of $\sim\! 3$–$4\, \mathrm{kyr}$. The expected difficulty in producing such massive thermally relaxed objects, together with recent results for currently preferred rapidly accreting formation models, suggests that such ‘truly direct’ or ‘dark’ collapses may not be typical for supermassive objects in the early Universe. We close by discussing the evolution of supermassive stars in the broader context of massive primordial stellar evolution and the possibility of supermassive stellar explosions.

scholarly journals Boron depletion in 9 to 15 M⊙ stars with rotation

2009 ◽  
Vol 5 (S268) ◽  
pp. 421-422
Author(s):  
U. Frischknecht ◽  
R. Hirschi ◽  
G. Meynet ◽  
S. Ekström ◽  
C. Georgy ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Massive Stars ◽  
Nitrogen Enrichment ◽  
Rotating Stars ◽  
Mixing Processes ◽  
The Real ◽  
Real Effects ◽  
M Stars ◽  
Open Question

AbstractThe treatment of mixing is still one of the major uncertainties in stellar evolution models. One open question is how well the prescriptions for rotational mixing describe the real effects. We tested the mixing prescriptions included in the Geneva stellar evolution code (GENEC) by following the evolution of surface abundances of light isotopes in massive stars, such as boron and nitrogen. We followed 9, 12 and 15 M⊙ models with rotation from the zero age main sequence up to the end of He burning. The calculations show the expected behaviour with faster depletion of boron for faster rotating stars and more massive stars. The mixing at the surface is more efficient than predicted by prescriptions used in other codes and reproduces the majority of observations very well. However two observed stars with strong boron depletion but no nitrogen enrichment still can not be explained and let the question open whether additional mixing processes are acting in these massive stars.

scholarly journals The growth of H ii regions around massive stars: the role of metallicity and dust

2020 ◽  
Author(s):  
Ahmad A Ali
Keyword(s):  
Star Formation ◽  
Radiation Pressure ◽  
Massive Stars ◽  
Particle Method ◽  
Diffuse Radiation ◽  
Uv Absorption ◽  
Expansion Velocity ◽  
H Ii Regions ◽  
Metal Line ◽  
Neutral Gas

Abstract Gas metallicity Z and the related dust-to-gas ratio fd can influence the growth of H ii regions via metal line cooling and UV absorption. We model these effects in star-forming regions containing massive stars. We compute stellar feedback from photoionization and radiation pressure (RP) using Monte Carlo radiative transfer coupled with hydrodynamics, including stellar and diffuse radiation fields. We follow a 105 M⊙ turbulent cloud with Z/Z⊙ = 2, 1, 0.5, 0.1 and fd = 0.01Z/Z⊙ with a cluster-sink particle method for star formation. The models evolve for at least 1.5Myr under feedback. Lower Z results in higher temperatures and therefore larger H ii regions. For Z ≥ Z⊙, radiation pressure Prad can dominate locally over the gas pressure Pgas in the inner half-parsec around sink particles. Globally, the ratio of Prad/Pgas is around 1 (2Z⊙), 0.3 (Z⊙), 0.1 (0.5Z⊙), and 0.03 (0.1Z⊙). In the solar model, excluding RP results in an ionized volume several times smaller than the fiducial model with both mechanisms. Excluding RP and UV attenuation by dust results in a larger ionized volume than the fiducial case. That is, UV absorption hinders growth more than RP helps it. The radial expansion velocity of ionized gas reaches +15km s−1 outwards, while neutral gas has inward velocities for most of the runtime, except for 0.1Z⊙ which exceeds +4km s−1. Z and fd do not significantly alter the star formation efficiency, rate, or cluster half-mass radius, with the exception of 0.1Z⊙ due to the earlier expulsion of neutral gas.

scholarly journals Pulsation and mass loss across the H-R diagram: From OB stars to Cepheids to red supergiants

2013 ◽  
Vol 9 (S301) ◽  
pp. 205-212
Author(s):  
Hilding R. Neilson
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Main Sequence ◽  
Massive Stars ◽  
Main Sequence Stars ◽  
Ob Stars ◽  
Classical Cepheids ◽  
Growing Body ◽  
Red Supergiants ◽  
Enhance Mass

AbstractBoth pulsation and mass loss are commonly observed in stars and are important ingredients for understanding stellar evolution and structure, especially for massive stars. There is a growing body of evidence that pulsation can also drive and enhance mass loss in massive stars and that pulsation-driven mass loss is important for stellar evolution. In this review, I will discuss recent advances in understanding pulsation-driven mass loss in massive main-sequence stars, classical Cepheids and red supergiants and present some challenges remaining.

scholarly journals Hollow H II Regions: From Giant to Ultracompact

1987 ◽  
Vol 115 ◽  
pp. 198-200 ◽  
Author(s):  
T. Montmerle ◽  
H. Dorland ◽  
C. Doom
Keyword(s):  
Heat Conduction ◽  
Stellar Evolution ◽  
Massive Stars ◽  
Temperature Gradients ◽  
Stellar Winds ◽  
H Ii Regions ◽  
Thick Shell ◽  
X Ray ◽  
The Standard Model ◽  
Theoretical Developments

H II regions around OB associations have a thick-shell structure (see, e.g., the Carina and Rosette nebulae), and yet the standard “Hot Interstellar Bubble” model (e.g., Weaver et al. 1977) predicts thin H II shells around a large X-ray emitting volume, when associated with stellar winds. Observations suggest that strong dissipation must occur at the edge of the wind cavity: (i) expansion velocities there are much smaller than predicted by the standard model (e.g., Chu, 1983); (ii) in bubbles around WR stars, overabundances of N, He, etc., are seen, hence the need to cool these WR-produced elements down to observable temperatures (Kwitter, 1981). Also, two theoretical developments are important: (i) new stellar evolution models for massive stars, including mass loss and overshooting in convective cores (e.g., Doom, 1985); (ii) a non-linear theory for heat conduction with steep temperature gradients (Luciani et al. 1985).

scholarly journals Modeling High-Mass Star Formation and Ultracompact H ii Regions

2010 ◽  
Vol 6 (S270) ◽  
pp. 107-114 ◽  
Author(s):  
Ralf S. Klessen ◽  
Thomas Peters ◽  
Robi Banerjee ◽  
Mordecai-Mark Mac Low ◽  
Roberto Galván-Madrid ◽  
...  
Keyword(s):  
Ionizing Radiation ◽  
Massive Stars ◽  
Three Dimensional ◽  
High Mass ◽  
H Ii Regions ◽  
Mass Star ◽  
Unstable Flow ◽  
Interstellar Gas ◽  
Accretion Rates ◽  
Supernova Explosions

AbstractMassive stars influence the surrounding universe far out of proportion to their numbers through ionizing radiation, supernova explosions, and heavy element production. Their formation requires the collapse of massive interstellar gas clouds with very high accretion rates. We discuss results from the first three-dimensional simulations of the gravitational collapse of a massive, rotating molecular cloud core that include heating by both non-ionizing and ionizing radiation. Local gravitational instabilities in the accretion flow lead to the build-up of a small cluster of stars. These lower-mass companions subsequently compete with the high-mass star for the same common gas reservoir and limit its overall mass growth. This process is called fragmentation-induced starvation, and explains why massive stars are usually found as members of high-order stellar systems. These simulations also show that the H ii regions forming around massive stars are initially trapped by the infalling gas, but soon begin to fluctuate rapidly. Over time, the same ultracompact H ii region can expand anisotropically, contract again, and take on any of the observed morphological classes. The total lifetime of H ii regions is given by the global accretion timescale, rather than their short internal sound-crossing time. This solves the so-called lifetime problem of ultracompact H ii region. We conclude that the the most significant differences between the formation of low-mass and high-mass stars are all explained as the result of rapid accretion within a dense, gravitationally unstable flow.

scholarly journals The fates of massive stars: exploring uncertainties in stellar evolution with metisse

2020 ◽  
Vol 497 (4) ◽  
pp. 4549-4564
Author(s):  
Poojan Agrawal ◽  
Jarrod Hurley ◽  
Simon Stevenson ◽  
Dorottya Szécsi ◽  
Chris Flynn
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Massive Stars ◽  
Mass Range ◽  
Radial Expansion ◽  
Single Star ◽  
New Approach ◽  
Star Evolution ◽  
Order Of Magnitude ◽  
The Impact

ABSTRACT In the era of advanced electromagnetic and gravitational wave detectors, it has become increasingly important to effectively combine and study the impact of stellar evolution on binaries and dynamical systems of stars. Systematic studies dedicated to exploring uncertain parameters in stellar evolution are required to account for the recent observations of the stellar populations. We present a new approach to the commonly used single-star evolution (sse) fitting formulae, one that is more adaptable: method of interpolation for single star evolution (metisse). It makes use of interpolation between sets of pre-computed stellar tracks to approximate evolution parameters for a population of stars. We have used metisse with detailed stellar tracks computed by the modules for experiments in stellar astrophysics (mesa), the bonn evolutionary code (bec), and the Cambridge stars code. metisse better reproduces stellar tracks computed using the stars code compared to sse, and is on average three times faster. Using stellar tracks computed with mesa and bec, we apply metisse to explore the differences in the remnant masses, the maximum radial expansion, and the main-sequence lifetime of massive stars. We find that different physical ingredients used in the evolution of stars, such as the treatment of radiation-dominated envelopes, can impact their evolutionary outcome. For stars in the mass range 9–100 M⊙, the predictions of remnant masses can vary by up to 20 M⊙, while the maximum radial expansion achieved by a star can differ by an order of magnitude between different stellar models.

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