scholarly journals Determination of Aspect and Degree of Differential Rotation, From Line Profiles in Rapidly Rotating Stars

1968 ◽  
Vol 140 (2) ◽  
pp. 121-139 ◽  
Author(s):  
T. R. Stoeckley
Keyword(s):  
Differential Rotation ◽  
Line Profiles ◽  
Rotating Stars ◽  
Rapidly Rotating Stars

scholarly journals Absolute Wavelength Shifts — A New Diagnostic for Rapidly Rotating Stars

2004 ◽  
Vol 215 ◽  
pp. 27-32
Author(s):  
Dainis Dravins
Keyword(s):  
Accurate Determination ◽  
Stellar Atmospheres ◽  
Line Profiles ◽  
Rotating Stars ◽  
Spectral Shifts ◽  
Space Astrometry ◽  
Stellar Motion ◽  
Rapidly Rotating Stars ◽  
Surface Convection

Accuracies reached in space astrometry now permit the accurate determination of astrometric radial velocities, without any use of spectroscopy. Knowing this true stellar motion, spectral shifts intrinsic to stellar atmospheres can be identified, for instance gravitational redshifts and those caused by velocity fields on stellar surfaces. The astrometric accuracy is independent of any spectral complexity, such as the smeared-out line profiles of rapidly rotating stars. Besides a better determination of stellar velocities, this permits more precise studies of atmospheric dynamics, such as possible modifications of stellar surface convection (granulation) by rotation-induced forces, as well as a potential for observing meridional flows across stellar surfaces.

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 The Determination and Interpretation of the Rotation Parameter v sin i

2004 ◽  
Vol 215 ◽  
pp. 3-16 ◽  
Author(s):  
George W. Collins
Keyword(s):  
Rotation Period ◽  
Rotation Parameter ◽  
Spectral Lines ◽  
Rotating Stars ◽  
Stellar Rotation ◽  
Indirect Methods ◽  
Stellar Spectroscopy ◽  
Rapidly Rotating Stars

In this paper we review the development of the concept of the stellar rotation parameter commonly known as v sin i. We emphasize that the interpretation of the parameter in terms of physical characteristics of the star always depends on comparison with a model that is intended to represent the physical properties of the star. To that end we will trace the development of such models along with the observational means of determining the parameter. Emphasis will be place on the traditional methods involving stellar spectroscopy, but some attention will be place on indirect methods involving direct measurement of the rotation period and recent interferometric determination of stellar oblatness. In addition we will comment on recent techniques involving the simultaneous measurement of many spectral lines and synthetic spectra to improve the accuracy of rotational half-widths.The natural desire for simplicity of such models has often resulted in erroneous values for stellar parameters. This is particularly the case for the most rapidly rotating stars generally of early spectral type, but may also be present in some giants and supergiants where rapid rotation is difficult to detect. Finally, we will comment on the possibilities of improving the quality of both the measurement and interpretation of this important stellar rotation parameter.

scholarly journals The Reliability of Echelle Spectroscopy in Hot Rotating Star Research

2004 ◽  
Vol 193 ◽  
pp. 571-574 ◽  
Author(s):  
Petr Škoda ◽  
Miroslav Šlechta
Keyword(s):  
Line Profile ◽  
Data Reduction ◽  
Rotating Stars ◽  
Precise Data ◽  
Wide Line ◽  
Rotating Star ◽  
Rapidly Rotating Stars ◽  
Echelle Spectroscopy ◽  
General Reduction

AbstractFor hot and rapidly rotating stars, the considerably wide line profile is spread over several echelle orders and thus a precise data reduction before merging several spectral orders together is required to obtain reliable results. As we show, the usage of automatic pipelines or wrong application of general reduction procedures may result in periodic ripple disturbances in the shape of the apparent stellar continuum and by this way introduce considerable errors into the determination of fundamental astrophysical quantities as gravity and mass of the stars.

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