scholarly journals The evolved fast rotator Sargas

2018 ◽  
Vol 619 ◽  
pp. A167 ◽  
Author(s):  
A. Domiciano de Souza ◽  
K. Bouchaud ◽  
M. Rieutord ◽  
F. Espinosa Lara ◽  
B. Putigny
Keyword(s):  
Rotation Axis ◽  
Model Fitting ◽  
Rotation Velocity ◽  
Surface Flux ◽  
Stellar Structure ◽  
High Resolution Spectroscopy ◽  
Physical Parameters ◽  
Polar Regions ◽  
Stellar Rotation ◽  
Instability Strip

Context. Gravity darkening (GD) and flattening are important consequences of stellar rotation. The precise characterization of these effects across the Hertzsprung–Russell (H-R) diagram is crucial to a deeper understanding of stellar structure and evolution. Aims. We seek to characterize such important effects on Sargas (θ Scorpii), an evolved, fast-rotating, intermediate-mass (∼5 M⊙) star, located in a region of the H-R diagram where they have never been directly measured as far as we know. Methods. We use our numerical model CHARRON to analyze interferometric (VLTI/PIONIER) and spectroscopic (VLT/UVES) observations through a MCMC model-fitting procedure. The visibilities and closure phases from the PIONIER data are particularly sensitive to rotational flattening and GD. Adopting the Roche approximation, we investigate two GD models: (1) the β-model (Teff ∝ geff β), which includes the classical von Zeipel’s GD law, and (2) the ω-model, where the flux is assumed to be anti-parallel to geff. Results. Using this approach we measure several physical parameters of Sargas, namely, equatorial radius, mass, equatorial rotation velocity, mean Teff, inclination and position angle of the rotation axis, and β. In particular, we show that the measured β leads to a surface flux distribution equivalent to the one given by the ω-model. Thanks to our results, we also show that Sargas is most probably located in a rare and interesting region of the H-R diagram: within the Hertzsprung gap and over the hot edge of the instability strip (equatorial regions inside it and polar regions outside it because of GD). Conclusions. These results show once more the power of optical/infrared long-baseline interferometry, combined with high-resolution spectroscopy, to directly measure fast-rotation effects and stellar parameters, in particular GD. As was the case for a few fast rotators previously studied by interferometry, the ω-model provides a physically more profound description of Sargas’ GD, without the need of a β exponent. It will also be interesting to further investigate the implications of the singular location of such a fast rotator as Sargas in the H-R diagram.

scholarly journals Sub-resolution limit spatio-spectral information using Differential Speckle Interferometry

1995 ◽  
Vol 149 ◽  
pp. 360-364 ◽  
Author(s):  
S. Lagarde ◽  
L.J. Sánchez ◽  
R.G. Petrov
Keyword(s):  
Rotation Axis ◽  
Angular Separation ◽  
Rotation Velocity ◽  
Position Angle ◽  
Speckle Interferometry ◽  
High Resolution Spectroscopy ◽  
High Angular Resolution ◽  
Stellar Rotation ◽  
Resolution Limit ◽  
Rotating Star

AbstractDifferential Speckle Interferometry (DSI) combines high angular resolution techniques with medium to high resolution spectroscopy. For non resolved sources, it yields the displacement of the object photocenter with wavelength. Combined with the spectrum s (λ), can give information with spatial and/or spectral resolution well beyond the telescope or spectrograph limits. This complementarity is illustrated here with experimental results. For the binary system Capella, we measure the angular separation, separate the spectra of the components and derive the radial velocity difference and the rotation velocity of each component. For the slowly rotating star Aldebaran we obtain the position angle of the stellar rotation axis and a relation between the angular diameter and the rotation velocity which in this case gives the latest.

scholarly journals Statistical analysis of roAp, He-weak, and He-rich stars

2019 ◽  
Vol 487 (4) ◽  
pp. 5922-5931
Author(s):  
S Ghazaryan ◽  
G Alecian ◽  
A A Hakobyan
Keyword(s):  
Data Base ◽  
Statistical Tests ◽  
Rotation Velocity ◽  
High Resolution Spectroscopy ◽  
Published Data ◽  
Physical Parameters ◽  
Peculiar Stars ◽  
Abundance Anomalies ◽  
Chemically Peculiar Stars ◽  
Ap Stars

Abstract To enlarge our data base of chemically peculiar stars, we compiled published data concerning the He-weak and He-rich stars observed by high-resolution spectroscopy techniques during last decades. Twenty He-weak and 28 He-rich stars have been added to the data base. We have also distinguished roAp stars from stars previously identified as Ap stars. To deepen our knowledge on statistical overview of the abundance anomalies versus the physical parameters of stars, we compared our data with previous compilations. We applied statistical tests on our data and found interesting correlations for effective temperature and surface gravity for all type of stars and a few correlations for projected rotation velocity only for He-rich stars. Because of the lack of the data, we could not check whether being a member of binary system is affecting on chemical peculiarities of those stars.

scholarly journals Light curve variation caused by accretion column switching stellar hemispheres

2019 ◽  
Author(s):  
Miljenko Čemeljić ◽  
Michał Siwak
Keyword(s):  
Light Curve ◽  
Hot Spots ◽  
Rotation Axis ◽  
Three Dimensional ◽  
Column Switching ◽  
Stellar Surface ◽  
Physical Parameters ◽  
Stellar Rotation ◽  
Three Dimensional Model ◽  
Ring Section

Abstract We investigate switching of the accretion column between the stellar hemispheres in the magnetosphere of a star with the dipole magnetic field aligned with the stellar rotation axis. We show that such switching can produce “hiccups” in the observed lightcurves. The intensity of emitted radiation from the stellar surface as seen by distant observers is computed from our two dimensional axisymmetric viscous and resistive magnetohydrodynamic numerical simulations. This result is used to construct a three-dimensional model of a star with the ring-shaped hot spots from the accretion columns at the stellar surface. We compute the intensity from such hot spots. To obtain a non-axisymmetric model with arc-shaped hot spots, we remove a ring section in the azimuthal direction from the hot-spots and compute the intensity of the radiated emission. Such models can be used to relate physical parameters in the simulations to the observations. We show an example with the intensity computed from our model compared to observational light curve.

scholarly journals Connecting measurements of solar and stellar brightness variations

2020 ◽  
Vol 638 ◽  
pp. A56
Author(s):  
N.-E. Nèmec ◽  
E. Işık ◽  
A. I. Shapiro ◽  
S. K. Solanki ◽  
N. A. Krivova ◽  
...  
Keyword(s):  
Transport Model ◽  
Rotation Axis ◽  
Surface Flux ◽  
Light Curves ◽  
The Sun ◽  
Solar Cycles ◽  
Stellar Rotation ◽  
Flux Transport ◽  
Surface Distribution ◽  
The Difference

Context. A comparison of solar and stellar brightness variations is hampered by the difference in spectral passbands that are used in observations, and also by the possible difference in the inclination of the solar and stellar rotation axes from the line of sight. Aims. We calculate the rotational variability of the Sun as it would be measured in passbands used for stellar observations. In particular, we consider the filter systems used by the CoRoT, Kepler, TESS, and Gaia space missions. We also quantify the effect of the inclination of the rotation axis on the solar rotational variability. Methods. We employed the spectral and total irradiance reconstruction (SATIRE) model to calculate solar brightness variations in different filter systems as observed from the ecliptic plane. We then combined the simulations of the surface distribution of the magnetic features at different inclinations using a surface flux transport model with the SATIRE calculations to compute the dependence of the variability on the inclination. Results. For an ecliptic-bound observer, the amplitude of the solar rotational variability, as observed in the total solar irradiance (TSI), is 0.68 mmag (averaged over solar cycles 21–24). We obtained corresponding amplitudes in the Kepler (0.74 mmag), CoRoT (0.73 mmag), TESS (0.62 mmag), Gaia G (0.74 mmag), Gaia GRP (0.62 mmag), and Gaia GBP (0.86 mmag) passbands. Decreasing the inclination of the rotation axis decreases the rotational variability. For a sample of randomly inclined stars, the variability is on average 15% lower in all filter systems we considered. This almost compensates for the difference in amplitudes of the variability in TSI and Kepler passbands, making the amplitudes derived from the TSI records an ideal representation of the solar rotational variability for comparison to Kepler stars with unknown inclinations. Conclusions. The TSI appears to be a relatively good measure of solar variability for comparisons with stellar measurements in the CoRoT, Kepler, TESS Gaia G, and Gaia GRP filters. Whereas the correction factors can be used to convert the variability amplitude from solar measurements into the values expected for stellar missions, the inclination affects the shapes of the light curves so that a much more sophisticated correction than simple scaling is needed to obtain light curves out of the ecliptic for the Sun.

scholarly journals Rotation of the asymptotic giant branch star R Doradus

2018 ◽  
Vol 613 ◽  
pp. L4 ◽  
Author(s):  
W. H. T. Vlemmings ◽  
T. Khouri ◽  
E. De Beck ◽  
H. Olofsson ◽  
G. García-Segura ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Mass Loss ◽  
Rotation Axis ◽  
Rotational Velocity ◽  
Rotation Velocity ◽  
Asymptotic Giant Branch ◽  
High Angular Resolution ◽  
Stellar Rotation ◽  
Angular Rotation ◽  
Asymptotic Giant Branch Star

High-resolution observations of the extended atmospheres of asymptotic giant branch (AGB) stars can now directly be compared to the theories that describe stellar mass loss. Using Atacama Large Millimeter/submillimeter Array (ALMA) high angular resolution (30 × 42 mas) observations, we have for the first time resolved stellar rotation of an AGB star, R Dor. We measure an angular rotation velocity of ωR sin i = (3.5 ± 0.3) × 10−9 rad s−1, which indicates a rotational velocity of |υrot sin i| = 1.0 ± 0.1 km s−1 at the stellar surface (R* = 31.2 mas at 214 GHz). The rotation axis projected on the plane of the sky has a position angle Φ = 7 ± 6°. We find that the rotation of R Dor is two orders of magnitude faster than expected for a solitary AGB star that will have lost most of its angular momentum. Its rotational velocity is consistent with angular momentum transfer from a close companion. As a companion has not been directly detected, we suggest R Dor has a low-mass, close-in companion. The rotational velocity approaches the critical velocity, set by the local sound speed in the extended envelope, and is thus expected to affect the mass-loss characteristics of R Dor.

scholarly journals An extensive photometric study of the Blazhko RR Lyrae star RZ Lyr*

2012 ◽  
Vol 423 (2) ◽  
pp. 993-1005 ◽  
Author(s):  
J. Jurcsik ◽  
Á. Sódor ◽  
G. Hajdu ◽  
B. Szeidl ◽  
Á. Dózsa ◽  
...  
Keyword(s):  
Light Curve ◽  
Light Curves ◽  
Stellar Structure ◽  
Time Base ◽  
Photometric Method ◽  
Physical Parameters ◽  
Component Solution ◽  
Rr Lyrae ◽  
Curve Variation ◽  
Type Variable

Abstract The analysis of recent, extended multicolour CCD and archive photoelectric, photographic and visual observations has revealed several important properties of RZ Lyr, an RRab-type variable exhibiting large-amplitude Blazhko modulation. On the time base of ∼110 yr, a strict anticorrelation between the pulsation- and modulation-period changes is established. The light curve of RZ Lyr shows a remarkable bump on the descending branch in the small-amplitude phase of the modulation, similarly to the light curves of bump Cepheids. We speculate that the stellar structure temporally suits a 4:1 resonance between the periods of the fundamental and one of the higher order radial modes in this modulation phase. The light-curve variation of RZ Lyr can be correctly fitted with a two-modulation-component solution; the 121-d period of the main modulation is nearly but not exactly four times longer than the period of the secondary modulation component. Using the inverse photometric method, the variations in the pulsation-averaged values of the physical parameters in different phases of both modulation components are determined.

Impacts of Rotation Axis and Frequency on Vestibular Perceptual Thresholds

2022 ◽  
pp. 1-29
Author(s):  
Andrew R. Wagner ◽  
Megan J. Kobel ◽  
Daniel M. Merfeld
Keyword(s):  
Multisensory Integration ◽  
Rotation Axis ◽  
Semicircular Canals ◽  
Rotation Velocity ◽  
Pass Filter ◽  
Motion Cues ◽  
Left Posterior ◽  
Rotation Plane ◽  
Self Motion ◽  
Lower Frequencies

Abstract In an effort to characterize the factors influencing the perception of self-motion rotational cues, vestibular self-motion perceptual thresholds were measured in 14 subjects for rotations in the roll and pitch planes, as well as in the planes aligned with the anatomic orientation of the vertical semicircular canals (i.e., left anterior, right posterior; LARP, and right anterior, left posterior; RALP). To determine the multisensory influence of concurrent otolith cues, within each plane of motion, thresholds were measured at four discrete frequencies for rotations about earth-horizontal (i.e., tilts; EH) and earth-vertical axes (i.e., head positioned in the plane of the rotation; EV). We found that the perception of rotations, stimulating primarily the vertical canals, was consistent with the behavior of a high-pass filter for all planes of motion, with velocity thresholds increasing at lower frequencies of rotation. In contrast, tilt (i.e, EH rotation) velocity thresholds, stimulating both the canals and otoliths (i.e., multisensory integration), decreased at lower frequencies and were significantly lower than earth-vertical rotation thresholds at each frequency below 2 Hz. These data suggest that multisensory integration of otolithic gravity cues with semicircular canal rotation cues enhances perceptual precision for tilt motions at frequencies below 2 Hz. We also showed that rotation thresholds, at least partially, were dependent on the orientation of the rotation plane relative to the anatomical alignment of the vertical canals. Collectively these data provide the first comprehensive report of how frequency and axis of rotation influence perception of rotational self-motion cues stimulating the vertical canals.

scholarly journals Pulsations of Ob-Stars: New Observations

1998 ◽  
Vol 185 ◽  
pp. 347-354 ◽  
Author(s):  
Dietrich Baade
Keyword(s):  
Main Sequence ◽  
Physical Parameters ◽  
Be Stars ◽  
Instability Strip ◽  
Ob Stars ◽  
Analysis Strategies ◽  
The Galaxy ◽  
Order Line ◽  
Nonradial Pulsation ◽  
Radial Pulsations

Improved observing and data analysis strategies have initiated a considerable expansion of the empirical knowledge about the pulsations of OB stars. Possible correlations between physical parameters and associated pulsation characteristics are becoming more clearly perceivable. This starts to include the asteroseismologically fundamental areas of g-modes and rapid rotation. The β Cephei instability strip continues to be the only locus where radial pulsations occur (but apparently not in all stars located in that strip). Except for spectral types B8/B9 near the main sequence, where pulsations are hardly detected even at low amplitudes, any major group of stars in the Galaxy that are obviously not candidate pulsators still remains to be identified. However, the incidence and amplitudes of OB star pulsations decrease steeply with metallicity. The behaviour of high-luminosity stars is less often dominated by very few modes. In broad-lined stars the moving-bump phenomenon is more common than low-order line-profile variability. But its relation to nonradial pulsation is not clear. The beating of low-ℓ nonradial pulsation modes that have identical angular mode indices may be the clockwork of the outbursts of at least some Be stars. The physics of this episodic mass loss process remains to be identified.

scholarly journals Search for Magnetic Stars at Early Stages of Evolution

1993 ◽  
Vol 137 ◽  
pp. 669-671
Author(s):  
Yu. V. Glagolevskij
Keyword(s):  
Magnetic Field ◽  
Main Sequence ◽  
Rotation Velocity ◽  
Electric Vector ◽  
Magnetic Star ◽  
Stellar Rotation ◽  
Magnetic Stars ◽  
Hydrogen Lines ◽  
Direction Of Polarization ◽  
Gaseous Envelope

Young stars, as a rule, are too faint for measurements of magnetic field either by photographic method with the use of Zeeman analizer, or photoelectrically from hydrogen lines. That is why it is necessary to look for indirect ways of magnetic field detection, for example, by measurement of polarization. Ae/Be Herbig stars without a magnetic field are surrounded by a gaseous envelope in the form of a globe or a spheroid, flattened along the rotational axes (as dependent on stellar rotation velocity), and also by a gaseous-dust accretion disc in the plane of equator. There are powerful flows in gaseous envelopes of stars, connected with mass loss and accretion. If a star is a magnetic oblique rotator (as a magnetic star of the Main Sequence), then the gaseous envelope may acquire the shape of alon-gated ellipsoid with the major axes coincident with that of dipole (Dolginov et al., 1979). From the poles there arises a jet flow controlled by a magnetic field, as in He-r and He-w stars, having already reached the Main Sequence (Barker et al., 1982). Calculations show (Dolginov et al., 1979), that maximum polarization in the extended envelope p ≈ 4% arises when the ratio of ellipsoid axes is ≈ 2.5b. The electric vector of the dominating oscillation of the light wave is perpendicular to the plane through the axis of symmetry of the ellipsoid and the line of sight. Naturally, the magnetosphere rotates together with the star, involving the gaseous envelope, resulting in the variation of the degree and direction of polarization. Additional polarization is created by the polar jets, where the direction of the dominating oscillations of the electric vector is perpendicular to the axis of the polar stream, and value of maximal polarization may reach 5% along the beam.

scholarly journals Surface Abundances of Light Elements as Diagnostics of Transport Processes in the Sun and Solar-type stars

1990 ◽  
Vol 121 ◽  
pp. 437-448
Author(s):  
A. Baglin ◽  
Y. Lebreton
Keyword(s):  
Solar Surface ◽  
Rotation Velocity ◽  
Transport Processes ◽  
Physical Parameters ◽  
The Sun ◽  
Light Elements ◽  
Cosmic Abundance ◽  
Solar Type ◽  
The Moment ◽  
Slow Transport

AbstractObservations of the surface abundances of lithium, beryllium and helium-3 in the Sun and in solar-type stars of different ages should be interpreted in a coherent way. The abundance of lithium at the surface of a star decreases slowly with age; for stars of the same age it decreases with mass and a dependence on the rotation velocity is suggested. The solar surface lithium is depleted by a factor of 100 relative to the cosmic abundance while an He-3 enrichment of 15% at the solar surface during evolution is suggested.Observations favour the hypothesis of a slow transport process at work between the outer convective zone and the radiative interior of these stars. Orders of magnitude of the transport coefficient as well as its dependence upon the physical parameters can be inferred from surface abundances of light elements, but at the moment we are far from producing a completely consistent modelization.

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