scholarly journals Outflow from Protostars and Angular Momentum Transfer

2001 ◽  
Vol 200 ◽  
pp. 401-405
Author(s):  
Kohji Tomisaka
Keyword(s):  
Angular Momentum ◽  
Momentum Transfer ◽  
Main Sequence ◽  
Magnetic Torque ◽  
Main Sequence Stars ◽  
The Core ◽  
Mhd Simulations ◽  
Self Similar Solution ◽  
Self Similar ◽  
Almost All

Dynamical contraction of a slowly-rotating magnetized cloud is studied using 2D magnetohydrodynamical (MHD) simulations. In the isothermal stage (n ≲ nA ∼ 1010cm−3), the cloud evolves similarly to that expected from the Larson-Penston self-similar solution and experiences a run-away collapse. However, after the central density exceeds ∼ nA, an accretion disk is formed around an adiabatic core. Just outside the core, an outflow is ejected by the effect of magnetic torque (magneto-centrifugal wind). Since ∼ 10% of the mass is ejected with almost all the angular momentum, the specific angular momentum of the protostellar core reduces to that observed in pre-main-sequence stars.

Angular momentum transport in pre-main-sequence stars of intermediate mass

Solar Physics ◽  
1990 ◽  
Vol 128 (1) ◽  
pp. 287-298 ◽  
Author(s):  
C. Vigneron ◽  
A. Mangeney ◽  
C. Catala ◽  
E. Schatzman
Keyword(s):  
Angular Momentum ◽  
Main Sequence ◽  
Momentum Transport ◽  
Main Sequence Stars ◽  
Intermediate Mass ◽  
Angular Momentum Transport

scholarly journals The Origin of the RS CVn Binaries

1976 ◽  
Vol 73 ◽  
pp. 381-387 ◽  
Author(s):  
P. Biermann ◽  
D. S. Hall
Keyword(s):  
Angular Momentum ◽  
Star Formation ◽  
Total Mass ◽  
Total Angular Momentum ◽  
Main Sequence ◽  
Be Stars ◽  
Large Space ◽  
Single Star ◽  
The Core ◽  
Thermal Phase

We consider six possible origins for the RS CVn binaries based on the following possibilities. RS CVn binaries might now be either pre-main-sequence or post-main-sequence. A pre-main-sequence binary might not always have been a binary but might have resulted from fission of a rapidly rotating single pre-main-sequence star. The main-sequence counterparts might be either single stars or binaries.To decide which of the six origins is possible, we consider the following observed data for the RS CVn binaries: total mass, total angular momentum, lack of observed connection with regions of star formation, large space density, kinematical age, and the visual companion of WW Dra. In addition we consider lifetimes and space densities of single stars and other types of binaries.The only origin possible is that the RS CVn binaries are in a thermal phase following fission of a main-sequence single star. In this explanation the single star had a rapidly rotating core which became unstable due to the core contraction which made it begin to evolve off the main sequence. The present Be stars might be examples of such parent single stars.

scholarly journals Angular-Momemtum Transfer by Nonradial Oscillations in Massive Main-Sequence Stars

1993 ◽  
Vol 137 ◽  
pp. 287-289
Author(s):  
Umin Lee ◽  
Hideyuki Saio
Keyword(s):  
Angular Momentum ◽  
Reynolds Stress ◽  
Main Sequence ◽  
Rotation Velocity ◽  
Main Sequence Stars ◽  
Oscillation Analysis ◽  
Oscillation Velocity ◽  
Time Average ◽  
Linear Oscillation ◽  
Nonradial Oscillations

Angular mementum distribution is one of the most important factors for stellar structutre and evolution. Among other mechanisms, angular momentum is transfered by non-axisymmetric oscillations (nonradial oscillations). In this mechanism the angular momentum is carried mainly by the Reynolds stress, which is proportional to the product between radial and azimuthal components of oscillation velocity; i.e., (Φ direction is the direction of rotation velocity). In the linear oscillation analysis, the phase difference between and is with A finite value of δ, which arises from excitation or damping of the oscillation, makes the time average of finite. Positive angular momentum is transfered from the driving zone to the damping zone by a prograde mode (Osaki 1986).

scholarly journals The rotational evolution of young low mass stars

2007 ◽  
Vol 3 (S243) ◽  
pp. 231-240 ◽  
Author(s):  
Jérôme Bouvier
Keyword(s):  
Angular Momentum ◽  
Accretion Disk ◽  
Main Sequence ◽  
Young Stars ◽  
Sequence Evolution ◽  
Main Sequence Stars ◽  
Low Mass Stars ◽  
Rotational Evolution ◽  
Low Mass

AbstractStar-disk interaction is thought to drive the angular momentum evolution of young stars. In this review, I present the latest results obtained on the rotational properties of low mass and very low mass pre-main sequence stars. I discuss the evidence for extremely efficient angular momentum removal over the first few Myr of pre-main sequence evolution and describe recent results that support an accretion-driven braking mechanism. Angular momentum evolution models are presented and their implication for accretion disk lifetimes discussed.

scholarly journals The Rotation of Pre-Main Sequence Stars

1980 ◽  
Vol 5 ◽  
pp. 835-837
Author(s):  
Leonard V. Kuhi ◽  
Stuart Vogel
Keyword(s):  
Angular Momentum ◽  
Spectral Type ◽  
Main Sequence ◽  
Rotational Velocity ◽  
The Sun ◽  
Main Sequence Stars ◽  
Lower Mass ◽  
B Stars ◽  
Large Numbers ◽  
Rapid Deceleration

Kraft (1970) obtained the rotational velocities for large numbers of stars located in the field and in clusters of different ages. He noted that (a) among the field stars those stars with strong Call K emission had larger rotational velocities than those without; (b) stars in the Hyades and Pleiades (which are much younger than the field) had both larger rotational velocities and stronger Call K emission than field stars; (c) there was a pronounced break at spectral type early F in v sini as a function of spectral type and (d) the distribution of angular momentum per unit, mass J(M⊚) was proportional to M0.57 for main sequence stars with mass M > 1.5 Mʘ. This distribution predicted a v sini of ˜75 km/sec for stars of lower mass (e.g. G type) but such high velocities were not seen in the Pleiades nor in the sun. This implied a more rapid deceleration of v sini for lower mass stars and led to estimates of the e-folding time of ˜4×l08 years for stars of 1.2 M⊚ to reduce their v sini from that of the Pleiades to that of the Hyades and ˜4×l09 years to go from the Hyades to the sun’s v sini. We note also that the age of the Pleiades is approximately equal to the pre-main sequence lifetime of a 1.0 M0 star so that the zero-age main sequence cannot have J(M) α M0.57 for ˜1 M0 stars. Skumanich (1972) showed that both the Call k emission and the rotational velocity decayed as the (age)-½ for main-sequence stars.

scholarly journals The Rotation of Low-Mass Pre-Main-Sequence Stars

2004 ◽  
Vol 215 ◽  
pp. 113-122 ◽  
Author(s):  
Robert D. Mathieu
Keyword(s):  
Angular Momentum ◽  
Main Sequence ◽  
Rotation Period ◽  
Rotating Stars ◽  
Stellar Rotation ◽  
Main Sequence Stars ◽  
Star Forming ◽  
Rotation Periods ◽  
Order Of Magnitude ◽  
Critical Velocities

Major photometric monitoring campaigns of star-forming regions in the past decade have provided rich rotation period distributions of pre-main-sequence stars. The rotation periods span more than an order of magnitude in period, with most falling between 1 and 10 days. Thus the broad rotation period distributions found in 100 Myr clusters are already established by an age of 1 Myr. The most rapidly rotating stars are within a factor of 2-3 of their critical velocities; if angular momentum is conserved as they evolve to the ZAMS, these stars may come to exceed their critical velocities. Extensive efforts have been made to find connections between stellar rotation and the presence of protostellar disks; at best only a weak correlation has been found in the largest samples. Magnetic disk-locking is a theoretically attractive mechanism for angular momentum evolution of young stars, but the links between theoretical predictions and observational evidence remain ambiguous. Detailed observational and theoretical studies of the magnetospheric environments will provide better insight into the processes of pre-main-sequence stellar angular momentum evolution.

scholarly journals On the behavior of stellar rotation in the solar neighbourhood

2012 ◽  
Vol 8 (S294) ◽  
pp. 195-196
Author(s):  
Daniel B. de Freitas ◽  
J. R. De Medeiros
Keyword(s):  
Angular Momentum ◽  
Momentum Transfer ◽  
Main Sequence ◽  
Rotational Velocity ◽  
Close Binary ◽  
Stellar Rotation ◽  
Tidal Interactions ◽  
Formation And Evolution ◽  
Fundamental Physical ◽  
Better Than

AbstractRotation is a fundamental physical parameter in stellar astrophysics, playing an important role on the formation and evolution of stars. This parameter may also offer valuable information on stellar magnetism, mixing in the stellar interior, tidal interactions in close binary, as well as on angular momentum transfer and rotational breaking due to planets. The present work brings the results of an unprecedented study on the behavior of the distribution of the projected rotational velocity (v sin i) as a function of galactic position, on the basis of an unique sample of 14000 main-sequence field stars, along the spectral regions F and G. The vsini measurements used in this analyses were obtained from observations carried out with the CORAVEL spectrometers, with a precision better than about 1 km/s.

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