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

AbstractThe rotation rates in the interior and at the surface is determined for the 22 main-sequence stars with masses between 1.0 and 1.6 M⊙. The average interior rotation is measured using asteroseismology, while the surface rotation is measured by the spectroscopic v sin i or the periodic light variation due to surface structures, such as spots. It is found that the difference between the surface rotation rate determined by spectroscopy and the average rotation rate for most of stars is small enough to suggest that an efficient process of angular momentum transport operates during and/or before the main-sequence stage of stars. By comparing the surface rotation rate measured from the light variation with those measured by spectroscopy, we found hints of latitudinal differential rotation. However, this must be confirmed by a further study because our result is sensitive to a few data points.

Download Full-text

Tidally–Induced Angular Momentum Transport in Disks

Symposium - International Astronomical Union ◽

10.1017/s0074180900225461 ◽

2001 ◽

Vol 200 ◽

pp. 406-409 ◽

Cited By ~ 2

Author(s):

Caroline E. J. M. L. J. Terquem

Keyword(s):

Angular Momentum ◽

Main Sequence ◽

Dominant Role ◽

Momentum Transport ◽

Tidal Effects ◽

Mhd Turbulence ◽

Angular Momentum Transport ◽

Tidal Waves ◽

Protostellar Disks ◽

Bending Waves

We discuss the transport of angular momentum induced by tidal effects in a disk surrounding a star in a pre–main sequence binary system. We consider the effect of both density and bending waves. Although tidal effects are important for truncating protostellar disks and for determining their size, it is unlikely that tidally–induced angular momentum transport plays a dominant role in the evolution of protostellar disks. Where the disk is magnetized, transport of angular momentum is probably governed by MHD turbulence. In a non self–gravitating laminar disk, the amount of transport provided by tidal waves is probably too small to account for the lifetime of protostellar disks. In addition, tidal effects tend to be localized in the disk outer regions.

Download Full-text

γ Doradus stars as a test of angular momentum transport models

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832607 ◽

2019 ◽

Vol 626 ◽

pp. A121 ◽

Cited By ~ 19

Author(s):

R.-M. Ouazzani ◽

J. P. Marques ◽

M.-J. Goupil ◽

S. Christophe ◽

V. Antoci ◽

...

Keyword(s):

Angular Momentum ◽

Main Sequence ◽

Evolutionary Models ◽

Intermediate Mass ◽

Angular Momentum Transport ◽

Rotation Rates ◽

Giant Stars ◽

Intermediate Mass Stars ◽

Red Giant ◽

Core Rotation

Helioseismology and asteroseismology of red giant stars have shown that distribution of angular momentum in stellar interiors, and the evolution of this distribution with time remains an open issue in stellar physics. Owing to the unprecedented quality and long baseline of Kepler photometry, we are able to seismically infer internal rotation rates in γ Doradus stars, which provide the main-sequence counterpart to the red-giants puzzle. Here, we confront these internal rotation rates to stellar evolution models which account for rotationally induced transport of angular momentum, in order to test angular momentum transport mechanisms. On the one hand, we used a stellar model-independent method developed by our team in order to obtain accurate, seismically inferred, buoyancy radii and near-core rotation for 37 γ Doradus stars observed by Kepler. We show that the stellar buoyancy radius can be used as a reliable evolution indicator for field stars on the main sequence. On the other hand, we computed rotating evolutionary models of intermediate-mass stars including internal transport of angular momentum in radiative zones, following the formalism developed in the series of papers started by Zahn (1992, A&A, 265, 115), with the CESTAM code. This code calculates the rotational history of stars from the birth line to the tip of the RGB. The initial angular momentum content has to be set initially, which is done here by fitting rotation periods in young stellar clusters. We show a clear disagreement between the near-core rotation rates measured in the sample and the rotation rates obtained from the evolutionary models including rotationally induced transport of angular momentum following Zahn’s prescriptions. These results show a disagreement similar to that of the Sun and red giant stars in the considered mass range. This suggests the existence of missing mechanisms responsible for the braking of the core before and along the main sequence. The efficiency of the missing mechanisms is investigated. The transport of angular momentum as formalized by Zahn and Maeder cannot explain the measurements of near-core rotation in main-sequence intermediate-mass stars we have at hand.

Download Full-text

The Evolution of Angular Momentum of Intermediate Mass Stars: From the Birthline to the Main Sequence

Symposium - International Astronomical Union ◽

10.1017/s0074180900195993 ◽

2004 ◽

Vol 215 ◽

pp. 431-437

Author(s):

S. C. Wolff ◽

S. E. Strom ◽

L. A. Hillenbrand

Keyword(s):

Angular Momentum ◽

Accretion Disks ◽

Power Law ◽

Main Sequence ◽

Sharp Decrease ◽

Zero Point ◽

Main Sequence Stars ◽

Intermediate Mass ◽

Intermediate Mass Stars ◽

Continuous Power

Measurements of stars in the Orion OB association show that there is a continuous power law relationship between specific angular momentum (J/M) and mass (M) for stars on convective tracks having masses in the range ~0.5 to ~3 M⊙; this power law extends smoothly into the domain of more massive stars on the ZAMS. If we assume that stars are “locked” to circumstellar accretion disks via their magnetic fields until they are deposited on the stellar birthline, we can account for the observed slope and zero point of the power law fit to the upper envelope of the observed J/M vs M distribution.Pre-main sequence stars with M<2 M⊙ on radiative tracks do not follow the power law relationship. A sharp decrease in J/M with decreasing mass has been recognized for more than 30 years for older field stars, but remarkably is seen already among our Orion sample of stars that are only a few million years old. We show that this break in the power law is a consequence of loss of angular momentum on convective tracks, combined with core-envelope decoupling at the time of the transition from the convective to radiative tracks.

Download Full-text

Asteroseismology of evolved stars to constrain the internal transport of angular momentum

Astronomy and Astrophysics ◽

10.1051/0004-6361/202037568 ◽

2020 ◽

Vol 634 ◽

pp. L16 ◽

Cited By ~ 4

Author(s):

J. W. den Hartogh ◽

P. Eggenberger ◽

S. Deheuvels

Keyword(s):

Angular Momentum ◽

Stellar Evolution ◽

White Dwarf ◽

Momentum Transport ◽

Intermediate Mass ◽

Angular Momentum Transport ◽

Rotation Rates ◽

The Core ◽

Intermediate Mass Stars ◽

Core Rotation

Context. The internal characteristics of stars, such as their core rotation rates, are obtained via asteroseismic observations. A comparison of core rotation rates found in this way with core rotation rates as predicted by stellar evolution models demonstrate a large discrepancy. This means that there must be a process of angular momentum transport missing in the current theory of stellar evolution. A new formalism was recently proposed to fill in for this missing process, which has the Tayler instability as its starting point (by Fuller et al. 2019, MNRAS, 485, 3661, hereafter referred to as “Fuller-formalism”). Aims. We investigate the effect of the Fuller-formalism on the internal rotation of stellar models with an initial mass of 2.5 M⊙. Methods. Stellar evolution models, including the Fuller-formalism, of intermediate-mass stars were calculated to make a comparison between asteroseismically obtained core rotation rates in the core He burning phase and in the white dwarf phase. Results. Our main results show that models including the Fuller-formalism can match the core rotation rates obtained for the core He burning phases. However, these models are unable to match the rotation rates obtained for white dwarfs. When we exclude the Fuller-formalism at the end of the core He burning phase, the white dwarf rotation rates of the models match the observed rates. Conclusions. We conclude that in the present form, the Fuller-formalism cannot be the sole solution for the missing process of angular momentum transport in intermediate-mass stars.

Download Full-text