scholarly journals Pillars, Jets and Dynamical Features

2010 ◽  
Vol 6 (S270) ◽  
pp. 319-322
Author(s):  
Matthias Gritschneder ◽  
Andreas Burkert ◽  
Thorsten Naab ◽  
Stefanie Walch
Keyword(s):  
Molecular Clouds ◽  
Hii Regions ◽  
Parameter Study ◽  
Low Mass Stars ◽  
Physical Conditions ◽  
Gravitational Forces ◽  
Irregular Structures ◽  
Low Mass ◽  
Dynamical Features ◽  
The Impact

AbstractWe present high resolution simulations on the impact of ionizing radiation on turbulent molecular clouds. The combination of hydrodynamics, gravitational forces and ionization in the tree-SPH code iVINE naturally leads to the formation of elongated filaments and clumps, which are in excellent agreement with the pillars observed around HII regions. Including gravity the formation of a second generation of low-mass stars with surrounding protostellar disks is triggered at the tips of the pillars, as also observed. A parameter study allows us to determine the physical conditions under which irregular structures form and whether they resemble large pillars or a system of small, isolated globules.

The impact of magnetism on tidal dynamics in the convective envelope of low-mass stars

2019 ◽  
Vol 15 (S354) ◽  
pp. 195-199
Author(s):  
A. Astoul ◽  
S. Mathis ◽  
C. Baruteau ◽  
F. Gallet ◽  
A. Strugarek ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Orbital Evolution ◽  
Magnetic Contribution ◽  
Low Mass Stars ◽  
Convective Envelope ◽  
Tidal Waves ◽  
Tidal Interactions ◽  
Rotational Evolution ◽  
Low Mass ◽  
The Impact

AbstractFor the shortest period exoplanets, star-planet tidal interactions are likely to have played a major role in the ultimate orbital evolution of the planets and on the spin evolution of the host stars. Although low-mass stars are magnetically active objects, the question of how the star’s magnetic field impacts the excitation, propagation and dissipation of tidal waves remains open. We have derived the magnetic contribution to the tidal interaction and estimated its amplitude throughout the structural and rotational evolution of low-mass stars (from K to F-type). We find that the star’s magnetic field has little influence on the excitation of tidal waves in nearly circular and coplanar Hot-Jupiter systems, but that it has a major impact on the way waves are dissipated.

scholarly journals Erosion of an exoplanetary atmosphere caused by stellar winds

2019 ◽  
Vol 630 ◽  
pp. A52 ◽  
Author(s):  
J. M. Rodríguez-Mozos ◽  
A. Moya
Keyword(s):  
Stellar Wind ◽  
Extreme Environment ◽  
Stellar Winds ◽  
Habitable Zone ◽  
Low Mass Stars ◽  
Zone Versus ◽  
Low Mass ◽  
The Difference ◽  
Interaction Regions ◽  
The Impact

Aims. We present a formalism for a first-order estimation of the magnetosphere radius of exoplanets orbiting stars in the range from 0.08 to 1.3 M⊙. With this radius, we estimate the atmospheric surface that is not protected from stellar winds. We have analyzed this unprotected surface for the most extreme environment for exoplanets: GKM-type and very low-mass stars at the two limits of the habitable zone. The estimated unprotected surface makes it possible to define a likelihood for an exoplanet to retain its atmosphere. This function can be incorporated into the new habitability index SEPHI. Methods. Using different formulations in the literature in addition to stellar and exoplanet physical characteristics, we estimated the stellar magnetic induction, the main characteristics of the stellar wind, and the different star-planet interaction regions (sub- and super-Alfvénic, sub- and supersonic). With this information, we can estimate the radius of the exoplanet magnetopause and thus the exoplanet unprotected surface. Results. We have conducted a study of the auroral aperture angles for Earth-like exoplanets orbiting the habitable zone of its star, and found different behaviors depending on whether the star is in rotational saturated or unsaturated regimes, with angles of aperture of the auroral ring above or below 36°, respectively, and with different slopes for the linear relation between the auroral aperture angle at the inner edge of the habitable zone versus the difference between auroral aperture angles at the two boundaries of the habitable zone. When the planet is tidally locked, the unprotected angle increases dramatically to values higher than 40° with a low likelihood of keeping its atmosphere. When the impact of stellar wind is produced in the sub-Alfvénic regime, the likelihood of keeping the atmosphere is almost zero for exoplanets orbiting very close to their star, regardless of whether they are saturated or not.

scholarly journals Low-mass Star Formation: Observations

2010 ◽  
Vol 6 (S270) ◽  
pp. 25-32 ◽  
Author(s):  
Neal J. Evans
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Planet Formation ◽  
Mass Star ◽  
Low Mass Stars ◽  
Chemical Changes ◽  
Open Questions ◽  
Low Mass ◽  
Over Time ◽  
The Imf

AbstractI briefly review recent observations of regions forming low mass stars. The discussion is cast in the form of seven questions that have been partially answered, or at least illuminated, by new data. These are the following: where do stars form in molecular clouds; what determines the IMF; how long do the steps of the process take; how efficient is star formation; do any theories explain the data; how are the star and disk built over time; and what chemical changes accompany star and planet formation. I close with a summary and list of open questions.

scholarly journals Does magnetic field impact tidal dynamics inside the convective zone of low-mass stars along their evolution?

2019 ◽  
Vol 631 ◽  
pp. A111 ◽  
Author(s):  
A. Astoul ◽  
S. Mathis ◽  
C. Baruteau ◽  
F. Gallet ◽  
A. Strugarek ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Scaling Laws ◽  
Low Mass Stars ◽  
Convective Envelope ◽  
Tidal Waves ◽  
Short Period ◽  
Tidal Flows ◽  
Low Mass ◽  
The Impact

Context. The dissipation of the kinetic energy of wave-like tidal flows within the convective envelope of low-mass stars is one of the key physical mechanisms that shapes the orbital and rotational dynamics of short-period exoplanetary systems. Although low-mass stars are magnetically active objects, the question of how the star’s magnetic field impacts large-scale tidal flows and the excitation, propagation and dissipation of tidal waves still remains open. Aims. Our goal is to investigate the impact of stellar magnetism on the forcing of tidal waves, and their propagation and dissipation in the convective envelope of low-mass stars as they evolve. Methods. We have estimated the amplitude of the magnetic contribution to the forcing and dissipation of tidally induced magneto-inertial waves throughout the structural and rotational evolution of low-mass stars (from M to F-type). For this purpose, we have used detailed grids of rotating stellar models computed with the stellar evolution code STAREVOL. The amplitude of dynamo-generated magnetic fields is estimated via physical scaling laws at the base and the top of the convective envelope. Results. We find that the large-scale magnetic field of the star has little influence on the excitation of tidal waves in the case of nearly-circular orbits and coplanar hot-Jupiter planetary systems, but that it has a major impact on the way waves are dissipated. Our results therefore indicate that a full magneto-hydrodynamical treatment of the propagation and dissipation of tidal waves is needed to properly assess the impact of star-planet tidal interactions throughout the evolutionary history of low-mass stars hosting short-period massive planets.

scholarly journals Asteroseismology of low-mass stars: the balance between partial ionization and Coulomb interactions

2021 ◽  
Vol 507 (4) ◽  
pp. 5747-5757
Author(s):  
Ana Brito ◽  
Ilídio Lopes
Keyword(s):  
Electrostatic Interactions ◽  
Chemical Elements ◽  
Acoustic Oscillation ◽  
Coulomb Interactions ◽  
Low Mass Stars ◽  
Stellar Oscillations ◽  
Diagnostic Potential ◽  
Low Mass ◽  
Coulomb Effects ◽  
The Impact

ABSTRACT All cool stars with outer convective zones have the potential to exhibit stochastically excited stellar oscillations. In this work, we explore the outer layers of stars less massive than the Sun. In particular, we have computed a set of stellar models ranging from 0.4 to 0.9 M⊙ with the aim at determining the impact on stellar oscillations of two physical processes occurring in the envelopes of these stars. Namely, the partial ionization of chemical elements and the electrostatic interactions between particles in the outer layers. We find that alongside with partial ionization, Coulomb effects also impact the acoustic oscillation spectrum. We confirm the well-known result that as the mass of a star decreases, the electrostatic interactions between particles become relevant. We found that their impact on stellar oscillations increases with decreasing mass, and for the stars with the lowest masses (M ≲ 0.6 M⊙), it is shown that Coulomb effects dominate over partial ionization processes producing a strong scatter on the acoustic modes. The influence of Coulomb interactions on the sound-speed gradient profile produces a strong oscillatory behaviour with diagnostic potential for the future.

scholarly journals Search for young low-mass stars in a ROSAT selected sample south of the Taurus-Auriga molecular clouds

1997 ◽  
Vol 124 (3) ◽  
pp. 449-467 ◽  
Author(s):  
A. Magazzù ◽  
E. L. Martín ◽  
M. F. Sterzik ◽  
R. Neuhäuser ◽  
E. Covino ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
Low Mass Stars ◽  
Low Mass

scholarly journals Jets in Molecular Clouds

1984 ◽  
Vol 110 ◽  
pp. 299-301
Author(s):  
Arieh Königl
Keyword(s):  
Molecular Clouds ◽  
Direct Evidence ◽  
Optical Emission ◽  
Central Star ◽  
Radio Continuum ◽  
Low Mass Stars ◽  
General Direction ◽  
Low Mass ◽  
Motion Measurements ◽  
Infrared Sources

There is now growing evidence that the cosmic jet phenomenon manifests itself in a remarkable way in regions of active star formation embedded in dense molecular clouds. The first indications for oppositely directed, supersonic outflows from young stars were provided by molecular line observations (most notably of CO) which detected spatially separated regions of redshifted and blueshifted emission in association with embedded infrared sources. About twenty sources of this kind have been identified so far, and more are continuously being discovered; they typically have radii ∼1018 cm, velocities ∼10–50 km s−1, dynamical ages ∼104 yr, and energies ∼1046-1047 erg s−1 (see Bally and Lada 1983 for a review). Statistical arguments indicate that energetic outflows of this type are probably a common feature in stellar evolution, and that they occur in both massive and low-mass stars. Direct evidence that the outflows in many cases are highly collimated was subsequently provided by the detection of high-velocity Herbig-Haro objects (optical emission clumps with typical masses ∼10−5M⊙) along the axes of the bipolar CO lobes. Proper-motion measurements are now available for a number of these objects (e.g., Herbig and Jones 1981), and they invariably reveal that the velocity vectors (of typical magnitudes 200–400 km s−1) point away from the central star. The clumps are often found to consist of many sub-condensations which move independently with disparate speeds, but which nevertheless travel in the same general direction with an angular spread ≲ 10°. Finally, radio continuum observations (e.g., Cohen et al. 1982) and deep CCD images (e.g., Mundt and Fried 1983) have shown that the collimation of the outflows is already well established on scales of ≲ 1015 cm.

scholarly journals Constraining How Star Formation Proceeds: Surveys in the Sub-mm and FIR

2009 ◽  
Vol 5 (H15) ◽  
pp. 406-407
Author(s):  
Doug Johnstone
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Mass Star ◽  
Star Forming ◽  
Physical Conditions ◽  
Star Forming Regions ◽  
Dense Cores ◽  
Multi Wavelength ◽  
Low Mass ◽  
High Column

AbstractCoordinated multi-wavelength surveys of molecular clouds are providing strong constraints on the physical conditions within low-mass star-forming regions. In this manner, Perseus and Ophiuchus have been exceptional laboratories for testing the earliest phases of star formation. Highlights of these results are: (1) dense cores form only in high column density regions, (2) dense cores contain only a few percent of the cloud mass, (3) the mass distribution of the dense cores is similar to the IMF, (4) the more massive cores are most likely to contain embedded protostars, and (5) the kinematics of the dense cores and the bulk gas show significant coupling.

Star Formation, Supernovae and the Structure of Disk Galaxies

1988 ◽  
Vol 101 ◽  
pp. 493-508
Author(s):  
Michael A. Dopita ◽  
Mt. Stromlo
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Collective Effects ◽  
Disk Galaxies ◽  
Solar Mass ◽  
Low Mass Stars ◽  
T Tauri ◽  
Steady Rate ◽  
Supernova Explosions ◽  
Low Mass

AbstractA physical model for bi-modal star formation and the structure of the interstellar medium and the self-regulating evolution of disk galaxies is presented. Stars heavier than about one solar mass are produced as a result of collisions of molecular clouds or in cloud crushing events whereas low-mass stars are produced at a steady rate in dense molecular clouds and the T-Tauri winds resulting maintain the support of these clouds against rapid collapse and fragmentation. Supernova explosions and stellar winds associated with the massive stars maintain the phase structure, and the scale height of the gas. The collective effects of these energetic processes may create a hole in the disk gas, and allow a galactic wind of metalenriched gas to develop.

scholarly journals Deep inside low-mass stars

2008 ◽  
Vol 4 (S252) ◽  
pp. 163-174 ◽  
Author(s):  
Corinne Charbonnel ◽  
Suzanne Talon
Keyword(s):  
Large Scale ◽  
Main Sequence ◽  
Internal Gravity Waves ◽  
Transport Processes ◽  
Atomic Diffusion ◽  
Physical Processes ◽  
Low Mass Stars ◽  
Low Mass ◽  
Stellar Properties ◽  
The Impact

AbstractLow-mass stars exhibit, at all stages of their evolution, the signatures of complex physical processes that require challenging modeling beyond standard stellar theory. In this review, we recall the most striking observational evidences that probe the interaction and interdependence of various transport processes of chemicals and angular momentum in these objects. We then focus on the impact of atomic diffusion, large scale mixing due to rotation, and internal gravity waves on stellar properties on the main sequence and slightly beyond.

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