Long Baseline Interferometry of Rotating Stars Across the HR Diagram: Flattening, Gravity Darkening, Differential Rotation

2009 ◽  
pp. 171-194 ◽  
Author(s):  
A. Domiciano de Souza
Keyword(s):  
Differential Rotation ◽  
Rotating Stars ◽  
Long Baseline ◽  
Hr Diagram

scholarly journals Learning about Stellar Dynamos from Long–term Photometry of Starspots

1991 ◽  
Vol 130 ◽  
pp. 353-369 ◽  
Author(s):  
Douglas S. Hall
Keyword(s):  
Differential Rotation ◽  
Rotation Period ◽  
Turnover Time ◽  
Rotating Stars ◽  
Photometric Variability ◽  
Solar Type ◽  
Magnetic Cycles ◽  
The Many ◽  
Rapidly Rotating Stars

AbstractSpottedness, as evidenced by photometric variability in 277 late-type binary and single stars, is found to occur when the Rossby number is less than about 2/3. This holds true when the convective turnover time versus B–V relation of Gilliland is used for dwarfs and also for subgiants and giants if their turnover times are twice and four times longer, respectively, than for dwarfs. Differential rotation is found correlated with rotation period (rapidly rotating stars approaching solid-body rotation) and also with lobe-filling factor (the differential rotation coefficient k is 2.5 times larger for F = 0 than F = 1). Also reviewed are latitude extent of spottedness, latitude drift during a solar-type cycle, sector structure and preferential longitudes, starspot lifetimes, and the many observational manifestations of magnetic cycles.

scholarly journals Interferometric studies of rapid rotators

2010 ◽  
Vol 6 (S272) ◽  
pp. 44-55 ◽  
Author(s):  
Ming Zhao ◽  
John D. Monnier ◽  
Xiao Che
Keyword(s):  
Fundamental Property ◽  
Optical Interferometry ◽  
Rotating Stars ◽  
Stellar Rotation ◽  
Rapid Rotation ◽  
Long Baseline ◽  
Imaging Results ◽  
Basic Physics ◽  
Stellar Photosphere

AbstractStellar rotation, like stellar mass and metallicity, is a fundamental property of stars. Rapid rotation distorts the stellar photosphere and affects a star's luminosity, abundances and evolution. It is also linked to stellar wind and mass loss. The distortion of the stellar photosphere due to rapid rotation causes the stellar surface brightness and effective temperature to vary with latitude, leading to a bright pole and a dark equator - a phenomenon known as ‘Gravity Darkening’. Thanks to the development of long baseline optical interferometry in recent years, optical interferometers have resolved the elongation of rapidly rotating stars, and have even imaged a few systems for the first time, directly confirming the gravity darkening effect. In this paper, we review the recent interferometric studies of rapid rotators, particularly the imaging results from CHARA-MIRC. These sub-milliarcsecond resolution observations permit the determination of the inclination, the polar and equatorial radius and temperature, as well as the fractional rotation speed of several rapid rotators with unprecedented precision. The modeling also allows the determination of the true effective temperatures and luminosities of these stars, permitting the investigation of their true locations on the HR diagram. Discrepancies from standard models were also found in some measurements, suggesting the requirement of more sophisticated mechanisms such as non-uniform rotation in the model. These observations have demonstrated that optical interferometry is now sufficiently mature to provide valuable constraints and even model-independent images to shed light on the basic physics of stars.

scholarly journals Asymptotic theory of gravity modes in rotating stars

2018 ◽  
Vol 615 ◽  
pp. A106 ◽  
Author(s):  
V. Prat ◽  
S. Mathis ◽  
K. Augustson ◽  
F. Lignières ◽  
J. Ballot ◽  
...  
Keyword(s):  
Dispersion Relation ◽  
Differential Rotation ◽  
Chemical Elements ◽  
Hamiltonian Formalism ◽  
Stellar Model ◽  
Rotating Stars ◽  
Inertial Waves ◽  
Local Dispersion ◽  
Propagation Of Waves ◽  
The Impact

Context. Differential rotation has a strong influence on stellar internal dynamics and evolution, notably by triggering hydrodynamical instabilities, by interacting with the magnetic field, and more generally by inducing transport of angular momentum and chemical elements. Moreover, it modifies the way waves propagate in stellar interiors and thus the frequency spectrum of these waves, the regions they probe, and the transport they generate. Aims. We investigate the impact of a general differential rotation (both in radius and latitude) on the propagation of axisymmetric gravito-inertial waves. Methods. We use a small-wavelength approximation to obtain a local dispersion relation for these waves. We then describe the propagation of waves thanks to a ray model that follows a Hamiltonian formalism. Finally, we numerically probe the properties of these gravito-inertial rays for different regimes of radial and latitudinal differential rotation. Results. We derive a local dispersion relation that includes the effect of a general differential rotation. Subsequently, considering a polytropic stellar model, we observe that differential rotation allows for a large variety of resonant cavities that can be probed by gravito-inertial waves. We identify that for some regimes of frequency and differential rotation, the properties of gravito-inertial rays are similar to those found in the uniformly rotating case. Furthermore, we also find new regimes specific to differential rotation, where the dynamics of rays is chaotic. Conclusions. As a consequence, we expect modes to follow the same trend. Some parts of oscillation spectra corresponding to regimes similar to those of the uniformly rotating case would exhibit regular patterns, while parts corresponding to the new regimes would be mostly constituted of chaotic modes with a spectrum rather characterised by a generic statistical distribution.

scholarly journals Lithium and Rotation in Pop I stars

2004 ◽  
Vol 215 ◽  
pp. 234-239
Author(s):  
Sushma V. Mallik
Keyword(s):  
Main Sequence ◽  
Rotating Stars ◽  
One To One ◽  
Red Giant ◽  
Effects Of Rotation ◽  
Fast Rotating ◽  
Hr Diagram

Lithium abundances have been determined for 130 stars sampled on the basis that they have just about completed depletion of Li on the main sequence and have not yet begun their ascent on the red giant branch. The main goal is to study the effects of rotation on Li depletion. Analysis of the data reveals that fast rotating stars have suffered little depletion whereas slowly rotating stars have both low and high Li abundances. No one-to-one correlation appears to exist between Li abundance and the present v sini. The large observed spread in Li abundance is perhaps a consequence of an initial range in rotational velocities in stars spinning down to low values on the main sequence. An attempt is made to study the Li evolution as a function of age, mass and rotation against the backdrop of the evolutionary tracks on the HR diagram.

scholarly journals Gravito-inertial waves in a differentially rotating spherical shell

2016 ◽  
Vol 800 ◽  
pp. 213-247 ◽  
Author(s):  
G. M. Mirouh ◽  
C. Baruteau ◽  
M. Rieutord ◽  
J. Ballot
Keyword(s):  
Spherical Shell ◽  
Differential Rotation ◽  
Power Laws ◽  
Boussinesq Approximation ◽  
Theoretical Explanation ◽  
Heat Diffusion ◽  
Complex Spectrum ◽  
Rotating Stars ◽  
Inertial Waves ◽  
Short Period

The gravito-inertial waves propagating over a shellular baroclinic flow inside a rotating spherical shell are analysed using the Boussinesq approximation. The wave properties are examined by computing paths of characteristics in the non-dissipative limit, and by solving the full dissipative eigenvalue problem using a high-resolution spectral method. Gravito-inertial waves are found to obey a mixed-type second-order operator and to be often focused around short-period attractors of characteristics or trapped in a wedge formed by turning surfaces and boundaries. We also find eigenmodes that show a weak dependence with respect to viscosity and heat diffusion just like truly regular modes. Some axisymmetric modes are found unstable and likely destabilized by baroclinic instabilities. Similarly, some non-axisymmetric modes that meet a critical layer (or corotation resonance) can turn unstable at sufficiently low diffusivities. In all cases, the instability is driven by the differential rotation. For many modes of the spectrum, neat power laws are found for the dependence of the damping rates with diffusion coefficients, but the theoretical explanation for the exponent values remains elusive in general. The eigenvalue spectrum turns out to be very rich and complex, which lets us suppose an even richer and more complex spectrum for rotating stars or planets that own a differential rotation driven by baroclinicity.

Differential rotation on rapidly rotating stars

2007 ◽  
Vol 328 (10) ◽  
pp. 1030-1033 ◽  
Author(s):  
A. Collier Cameron
Keyword(s):  
Differential Rotation ◽  
Rotating Stars ◽  
Rapidly Rotating Stars
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