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

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.

scholarly journals IPHAS A-type Stars with Mid-IR Excesses in Spitzer Surveys

2009 ◽  
Vol 5 (H15) ◽  
pp. 815-815
Author(s):  
Antonio S. Hales ◽  
Michael J. Barlow ◽  
Janet E. Drew ◽  
Yvonne C. Unruh ◽  
Robert Greimel ◽  
...  
Keyword(s):  
Cross Correlation ◽  
Main Sequence ◽  
Terrestrial Planet ◽  
Circumstellar Disks ◽  
Main Sequence Stars ◽  
Intermediate Mass ◽  
Mid Infrared ◽  
Isaac Newton ◽  
Intermediate Mass Stars ◽  
Dust Disks

AbstractThe Isaac Newton Photometric H-Alpha Survey (IPHAS) provides (r′-Hα)-(r′-i′) colors, which can be used to select AV0-5 Main Sequence star candidates (age~20-200 Myr). By combining a sample of 23050 IPHAS-selected A-type stars with 2MASS, GLIMPSE and MIPSGAL photometry we searched for mid-infrared excesses attributable to dusty circumstellar disks. Positional cross-correlation yielded a sample of 2692 A-type stars, of which 0.6% were found to have 8-μm excesses above the expected photospheric values. The low fraction of main sequence stars with mid-IR excesses found in this work indicates that dust disks in the terrestrial planet zone of Main Sequence intermediate mass stars are rare. Dissipation mechanisms such as photo-evaporation, grain growth, collisional grinding or planet formation could possibly explain the depletion of dust detected in the inner regions of these disks.

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 γ Doradus stars as a test of angular momentum transport models

2019 ◽  
Vol 626 ◽  
pp. A121 ◽  
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.

scholarly journals The Population of Debris Discs Orbiting Subgiants

2013 ◽  
Vol 8 (S299) ◽  
pp. 328-329
Author(s):  
Amy Bonsor ◽  
Grant M. Kennedy ◽  
Justin R. Crepp ◽  
John A. Johnson ◽  
Mark C. Wyatt ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Main Sequence ◽  
Planetary Systems ◽  
Main Sequence Stars ◽  
Intermediate Mass ◽  
Intermediate Mass Stars

AbstractWhilst debris discs orbiting main-sequence stars are well studied, very little is known regarding their fate when the star evolves onto the giant branch. For intermediate mass (A-type) stars, giants provide a unique opportunity to detect planets using the radial velocity technique, otherwise prohibited by high jitter levels and rotationally broadened lines in main-sequence intermediate mass (A-type) stars. Such stars can provide key insights into the structure of planetary systems around intermediate mass stars. In our Herschel OT1 program (PI Bonsor) we searched for the presence of debris discs orbiting a sample of 36 subgiants, half of which have RV detected companions. Our best detection is the resolved debris disc orbiting κ CrB.

scholarly journals First evidence of inertial modes in γ Doradus stars: The core rotation revealed

2020 ◽  
Vol 640 ◽  
pp. A49
Author(s):  
R.-M. Ouazzani ◽  
F. Lignières ◽  
M.-A. Dupret ◽  
S. J. A. J. Salmon ◽  
J. Ballot ◽  
...  
Keyword(s):  
Main Sequence ◽  
Density Stratification ◽  
Uniform Density ◽  
Main Sequence Stars ◽  
Intermediate Mass ◽  
The Core ◽  
Intermediate Mass Stars ◽  
Convective Core ◽  
Coupling Factors ◽  
Core Rotation

The advent of space photometry with CoRoT and Kepler has allowed for the gathering of exquisite and extensive time series for a wealth of main-sequence stars, including γ Doradus stars, whose detailed seismology was not achievable from the ground. γ Doradus stars present an incredibly rich pulsation spectra, with gravito-inertial modes, in some cases supplemented with δ Scuti-like pressure modes – for the hybrid stars – and, in many cases, with Rossby modes. The present paper aims to show that in addition to these modes which have been established in the radiative envelope, pure inertial modes that are trapped in the convective core can be detected in Kepler observations of γ Doradus stars thanks to their resonance with the gravito-inertial modes. We started by using a simplified model of perturbations in a full sphere of uniform density. Under these conditions, the spectrum of pure inertial modes is known from analytical solutions of the so-called Poincaré equation. We then computed coupling factors, which helped select the pure inertial modes which interact best with the surrounding dipolar gravito-inertial modes. Using complete calculations of gravito-inertial modes in realistic models of γ Doradus stars, we are able to show that the pure inertial and gravito-inertial resonances appear as “dips” in the gravito-inertial mode period spacing series at spin parameters that are close to those predicted by the simple model. We find the first evidence of such dips in the Kepler γ Doradus star KIC 5608334. Finally, using complete calculations in isolated convective cores, we find that the spin parameters of the pure inertial and gravito-inertial resonances are also sensitive to the density stratification of the convective core. In conclusion, we have discovered that certain dips in gravito-inertial mode period spacings that have been observed in some Kepler stars are, in fact, signatures of resonances with pure-inertial modes that are trapped in the convective core. This holds the promise that it would be possible to finally access the central conditions, namely, the rotation and density stratification, of intermediate-mass stars in the main sequence.

scholarly journals Small and Intermediate Mass Stellar Evolution - Main Sequence and Close to It

1993 ◽  
Vol 137 ◽  
pp. 410-425 ◽  
Author(s):  
A. Noels ◽  
N. Grevesse
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Turbulent Diffusion ◽  
Main Sequence ◽  
Main Sequence Stars ◽  
Intermediate Mass ◽  
Physical Mechanisms ◽  
Standard Models

AbstractWe present the standard models for small and intermediate main sequence stars and we discuss some of the problems arising with semiconvection and overshooting. The surface abundance of Li serves as a test for other physical mechanisms, including microscopic and turbulent diffusion, rotation and mass loss.

scholarly journals The effects of Rotation on Wolf–Rayet Stars and on the Production of Primary Nitrogen by Intermediate Mass Stars

2004 ◽  
Vol 215 ◽  
pp. 579-588 ◽  
Author(s):  
Georges Meynet ◽  
Max Pettini
Keyword(s):  
Star Formation ◽  
Time Delay ◽  
Main Sequence ◽  
Massive Stars ◽  
Sequence Evolution ◽  
Stellar Rotation ◽  
Intermediate Mass ◽  
Intermediate Mass Stars ◽  
Solar Metallicity ◽  
Effects Of Rotation

We use the rotating stellar models described in the paper by A. Maeder & G. Meynet in this volume to consider the effects of rotation on the evolution of the most massive stars into and during the Wolf–Rayet phase, and on the post-Main Sequence evolution of intermediate mass stars. The two main results of this discussion are the following. First, we show that rotating models are able to account for the observed properties of the Wolf–Rayet stellar populations at solar metallicity. Second, at low metallicities, the inclusion of stellar rotation in the calculation of chemical yields can lead to a longer time delay between the release of oxygen and nitrogen into the interstellar medium following an episode of star formation, since stars of lower masses (compared to non-rotating models) can synthesize primary N. Qualitatively, such an effect may be required to explain the relative abundances of N and O in extragalactic metal–poor environments, particularly at high redshifts.

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 Pan-Pacific Planet Search – VIII. Complete results and the occurrence rate of planets around low-luminosity giants

2019 ◽  
Vol 491 (4) ◽  
pp. 5248-5257 ◽  
Author(s):  
Robert A Wittenmyer ◽  
R P Butler ◽  
Jonathan Horner ◽  
Jake Clark ◽  
C G Tinney ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Main Sequence ◽  
Giant Planets ◽  
Occurrence Rate ◽  
Velocity Measurements ◽  
Intermediate Mass ◽  
Giant Stars ◽  
Intermediate Mass Stars ◽  
Final Data ◽  
Solar Type

ABSTRACT Our knowledge of the populations and occurrence rates of planets orbiting evolved intermediate-mass stars lags behind that for solar-type stars by at least a decade. Some radial velocity surveys have targeted these low-luminosity giant stars, providing some insights into the properties of their planetary systems. Here, we present the final data release of the Pan-Pacific Planet Search (PPPS), a 5 yr radial velocity survey using the 3.9 m Anglo-Australian Telescope. We present 1293 precise radial velocity measurements for 129 stars, and highlight 6 potential substellar-mass companions, which require additional observations to confirm. Correcting for the substantial incompleteness in the sample, we estimate the occurrence rate of giant planets orbiting low-luminosity giant stars to be approximately 7.8$^{+9.1}_{-3.3}$ per cent. This result is consistent with the frequency of such planets found to orbit main-sequence A-type stars, from which the PPPS stars have evolved.

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.

Sign in / Sign up

Export Citation Format

Share Document