Line profile variations caused by low-frequency nonradial pulsations of rapidly rotating stars

Context. As of today, asteroseismology mainly allows us to probe the internal rotation of stars when modes are only weakly affected by rotation using perturbative methods. Such methods cannot be applied to rapidly rotating stars, which exhibit complex oscillation spectra. In this context, the so-called traditional approximation, which neglects the terms associated with the latitudinal component of the rotation vector, describes modes that are strongly affected by rotation. This approximation is sometimes used for interpreting asteroseismic data, however, its domain of validity is not established yet. Aims. We aim at deriving analytical prescriptions for period spacings of low-frequency gravity modes strongly affected by rotation through the full Coriolis acceleration (i.e. without neglecting any component of the rotation vector), which can be used to probe stellar internal structure and rotation. Methods. We approximated the asymptotic theory of gravito-inertial waves in uniformly rotating stars using ray theory described in a previous paper in the low-frequency regime, where waves are trapped near the equatorial plane. We put the equations of ray dynamics into a separable form and used the Einstein-Brillouin-Keller (EBK) quantisation method to compute modes frequencies from rays. Results. Two spectral patterns that depend on stratification and rotation are predicted within this new approximation: one for axisymmetric modes and one for non-axisymmetric modes. Conclusions. The detection of the predicted patterns in observed oscillation spectra would give constraints on internal rotation and chemical stratification of rapidly rotating stars exhibiting gravity modes, such as γ Doradus, SPB, or Be stars. The obtained results have a mathematical form that is similar to that of the traditional approximation, but the new approximation takes the full Coriolis, which allows for propagation near the centre, and centrifugal accelerations into account.

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A Comparison of the Anelastic and Subseismic Approximations for Low-Frequency Stellar Oscillations: an Application to Rapidly Rotating Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100015955 ◽

2002 ◽

Vol 185 ◽

pp. 186-189

Author(s):

B. Dintrans ◽

M. Rieutord

Keyword(s):

Acoustic Waves ◽

Low Frequency ◽

Rotating Stars ◽

Stellar Oscillations ◽

Rapidly Rotating Stars ◽

Better Than

AbstractAfter showing that the anelastic approximation is better than the subseismic one to filter out acoustic waves when studying low-frequency stellar oscillations, we compute gravito-inertial modes of a typical γ Doradus star using this approximation. We show that eigenmodes can be regular or singular, according to the possible focusing towards attractors of the underlying characteristics. Consequences on the oscillations spectrum are then discussed.

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Line Profile and Photometric Variations of the Be Star η Cen

International Astronomical Union Colloquium ◽

10.1017/s0252921100016183 ◽

2002 ◽

Vol 185 ◽

pp. 252-253

Author(s):

R. Levenhagen ◽

N. Leister ◽

E. Janot-Pacheco ◽

J. Zorec ◽

A. Hubert ◽

...

Keyword(s):

High Resolution ◽

Line Profile ◽

Rotational Frequency ◽

Current Status ◽

Be Stars ◽

Rotating Stars ◽

Fundamental Parameters ◽

Spectrophotometric Data ◽

Be Star ◽

Rapidly Rotating Stars

AbstractWe review the current status of our monitoring project on Be stars. Line profile variations in Helλ667.8 nm were detected in the Be star η Cen, by means of high resolution and S/N Spectroscopic observations. They were interpreted in terms of nonradial pulsations (NRP). The fundamental parameters of η Cen obtained from BCD spectrophotometric data and interpreted using models of rapidly rotating stars, have been used to estimate the stellar rotational frequency.

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Transport of angular momentum by stochastically excited waves as an explanation for the outburst of the rapidly rotating Be star HD49330

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935858 ◽

2020 ◽

Vol 644 ◽

pp. A9 ◽

Cited By ~ 1

Author(s):

C. Neiner ◽

U. Lee ◽

S. Mathis ◽

H. Saio ◽

C. C. Lovekin ◽

...

Keyword(s):

Angular Momentum ◽

Low Frequency ◽

Be Stars ◽

Rotating Stars ◽

Transient Waves ◽

Frequency Signal ◽

Unstable Phase ◽

Be Star ◽

2D Structure ◽

Rapidly Rotating Stars

Context. HD 49330 is an early Be star that underwent an outburst during its five-month observation with the CoRoT satellite. An analysis of its light curve revealed several independent p and g pulsation modes, in addition to showing that the amplitude of the modes is directly correlated with the outburst. Aims. We modelled the results obtained with CoRoT to understand the link between pulsational parameters and the outburst of this Be star. Methods. We modelled the flattening of the structure of the star due to rapid rotation in two ways: Chandrasekhar-Milne’s expansion and 2D structure computed with ROTORC. We then modelled κ-driven pulsations. We also adapted the formalism of the excitation and amplitude of stochastically excited gravito-inertial modes to rapidly rotating stars, and we modelled those pulsations as well. Results. We find that while pulsation p modes are indeed excited by the κ mechanism, the observed g modes are, rather, a result of stochastic excitation. In contrast, g and r waves are stochastically excited in the convective core and transport angular momentum to the surface, increasing its rotation rate. This destabilises the external layers of the star, which then emits transient stochastically excited g waves. These transient waves produce most of the low-frequency signal detected in the CoRoT data and ignite the outburst. During this unstable phase, p modes disappear at the surface because their cavity is broken. Following the outburst and ejection of the surface layer, relaxation occurs, making the transient g waves disappear and p modes reappear. Conclusions. This work includes the first coherent model of stochastically excited gravito-inertial pulsation modes in a rapidly rotating Be star. It provides an explanation for the correlation between the variation in the amplitude of frequencies detected in the CoRoT data and the occurrence of an outburst. This scenario could apply to other pulsating Be stars, providing an explanation to the long-standing questions surrounding Be outbursts and disks.

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Unified NRP-Modelling of Be Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100016134 ◽

2002 ◽

Vol 185 ◽

pp. 240-243 ◽

Cited By ~ 4

Author(s):

Th. Rivinius ◽

D. Baade ◽

S. Štefl ◽

M. Maintz

Keyword(s):

Line Profile ◽

Inclination Angle ◽

Be Stars ◽

Rotating Stars ◽

Early Type ◽

Rapidly Rotating Stars ◽

Nonradial Pulsation ◽

Low Order

AbstractRecently, the line profile variability (lpv) of two low-v sin i Be stars, μ Cen and ω (28) CMa was successfully modelled as nonradial pulsation (nrp) of rapidly rotating stars seen pole-on. In this work, it is shown that the lpv of low-v sin i early-type Be stars in general closely resembles these two cases, and is therefore explainable by the same mechanism. The lpv of intermediate to high-v sin i Be stars can be explained by the same model if the inclination angle of the model alone is increased. Consequently, early-type Be stars form a distinct, fairly homogeneous class of non-radial low-order g-mode pulsators.

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The Reliability of Echelle Spectroscopy in Hot Rotating Star Research

International Astronomical Union Colloquium ◽

10.1017/s0252921100011350 ◽

2004 ◽

Vol 193 ◽

pp. 571-574 ◽

Cited By ~ 1

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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Rossby Waves in Astrophysics

Space Science Reviews ◽

10.1007/s11214-021-00790-2 ◽

2021 ◽

Vol 217 (1) ◽

Author(s):

T. V. Zaqarashvili ◽

M. Albekioni ◽

J. L. Ballester ◽

Y. Bekki ◽

L. Biancofiore ◽

...

Keyword(s):

Large Scale ◽

Rossby Waves ◽

Magnetic Activity ◽

Future Research ◽

Rotating Stars ◽

Spatial And Temporal Scales ◽

Physical Role ◽

Astrophysical Objects ◽

Exoplanetary Atmospheres ◽

Rapidly Rotating Stars

AbstractRossby waves are a pervasive feature of the large-scale motions of the Earth’s atmosphere and oceans. These waves (also known as planetary waves and r-modes) also play an important role in the large-scale dynamics of different astrophysical objects such as the solar atmosphere and interior, astrophysical discs, rapidly rotating stars, planetary and exoplanetary atmospheres. This paper provides a review of theoretical and observational aspects of Rossby waves on different spatial and temporal scales in various astrophysical settings. The physical role played by Rossby-type waves and associated instabilities is discussed in the context of solar and stellar magnetic activity, angular momentum transport in astrophysical discs, planet formation, and other astrophysical processes. Possible directions of future research in theoretical and observational aspects of astrophysical Rossby waves are outlined.

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Learning about Stellar Dynamos from Long–term Photometry of Starspots

International Astronomical Union Colloquium ◽

10.1017/s0252921100079914 ◽

1991 ◽

Vol 130 ◽

pp. 353-369 ◽

Cited By ~ 2

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.

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