scholarly journals The rotation of α Oph investigated using polarimetry

2020 ◽  
Vol 494 (2) ◽  
pp. 2254-2267 ◽  
Author(s):  
Jeremy Bailey ◽  
Daniel V Cotton ◽  
Ian D Howarth ◽  
Fiona Lewis ◽  
Lucyna Kedziora-Chudczer
Keyword(s):  
Rotation Rate ◽  
Rotation Axis ◽  
Wavelength Dependence ◽  
Position Angle ◽  
Type Star ◽  
Sequence Evolution ◽  
Effects Of Rotation ◽  
Polar Radius ◽  
Rotating Star ◽  
Polarization Models

ABSTRACT Recently we have demonstrated that high-precision polarization observations can detect the polarization resulting from the rotational distortion of a rapidly rotating B-type star. Here, we investigate the extension of this approach to an A-type star. Linear-polarization observations of α Oph (A5IV) have been obtained over wavelengths from 400 to 750 nm. They show the wavelength dependence expected for a rapidly rotating star combined with a contribution from interstellar polarization. We model the observations by fitting rotating-star polarization models and adding additional constraints including a measured vesin i. However, we cannot fully separate the effects of rotation rate and inclination, leaving a range of possible solutions. We determine a rotation rate (ω = Ω/Ωc) between 0.83 and 0.98 and an axial inclination i > 60°. The rotation-axis position angle is found to be 142 ± 4°, differing by 16° from a value obtained by interferometry. This might be due to precession of the rotation axis due to interaction with the binary companion. Other parameters resulting from the analysis include a polar temperature Tp = 8725 ± 175 K, polar gravity log gp = 3.93 ± 0.08 (dex cgs), and polar radius Rp = 2.52 ± 0.06 R⊙. Comparison with rotating-star evolutionary models indicates that α Oph is in the later half of its main-sequence evolution and must have had an initial ω of 0.8 or greater. The interstellar polarization has a maximum value at a wavelength (λmax) of 440 ± 110 nm, consistent with values found for other nearby stars.

Rotation

2013 ◽  
Author(s):  
Gary A. Glatzmaier
Keyword(s):  
Spherical Shell ◽  
Accretion Disk ◽  
Gravity Waves ◽  
Equatorial Plane ◽  
Rotation Rate ◽  
Rate Of Change ◽  
Cylindrical Annulus ◽  
Planetary Rotation ◽  
Effects Of Rotation ◽  
Rotating Star

This chapter examines the effects of rotation on convection and gravity waves. Flows in the atmospheres, oceans, and liquid cores of terrestrial planets are dominated by the Coriolis forces, as are the interiors of giant planets and stars. The sum of gravitational and centrifugal forces can go to zero at the top boundary of a rapidly rotating star or accretion disk. The time rate of change of the planetary rotation rate gives rise to Poincaré forces. The chapter first considers Coriolis, centrifugal, and Poincaré forces before explaining the modifications needed to add these effects of rotation to previous models of convection and gravity waves in 2D cartesian box and cylindrical annulus geometries, both of which now lie within a rotating equatorial plane. It also describes 2.5D rotating models and 3D spherical-shell magnetohydrodynamic dynamo models.

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 Broadband Linear Polarization in Ap Stars

1993 ◽  
Vol 138 ◽  
pp. 305-309
Author(s):  
Marco Landolfi ◽  
Egidio Landi Degl’Innocenti ◽  
Maurizio Landi Degl’Innocenti ◽  
Jean-Louis Leroy ◽  
Stefano Bagnulo
Keyword(s):  
Magnetic Field ◽  
Circular Polarization ◽  
Linear Polarization ◽  
Rotation Axis ◽  
Spectral Lines ◽  
Line Of Sight ◽  
Long Time ◽  
Rotating Star ◽  
Ap Stars ◽  
The Magnetic Field

AbstractBroadband linear polarization in the spectra of Ap stars is believed to be due to differential saturation between σ and π Zeeman components in spectral lines. This mechanism has been known for a long time to be the main agent of a similar phenomenon observed in sunspots. Since this phenomenon has been carefully calibrated in the solar case, it can be confidently used to deduce the magnetic field of Ap stars.Given the magnetic configuration of a rotating star, it is possible to deduce the broadband polarization at any phase. Calculations performed for the oblique dipole model show that the resulting polarization diagrams are very sensitive to the values of i (the angle between the rotation axis and the line of sight) and β (the angle between the rotation and magnetic axes). The dependence on i and β is such that the four-fold ambiguity typical of the circular polarization observations ((i,β), (β,i), (π-i,π-β), (π-β,π-i)) can be removed.

Some effects of rotation rate on planetary ? scale wave flows

1996 ◽  
Vol 55 (1-4) ◽  
pp. 199-210
Author(s):  
G. -Q. Li ◽  
R. Kung ◽  
R. L. Pfeffer
Keyword(s):  
Rotation Rate ◽  
Planetary Scale ◽  
Effects Of Rotation ◽  
Wave Flows

scholarly journals Simultaneous Five Color (UBVRI) Polarimetry of VV Puppis

1987 ◽  
Vol 93 ◽  
pp. 203-203
Author(s):  
V. Piirola ◽  
A. Reiz ◽  
G.V. Coyne
Keyword(s):  
Circular Polarization ◽  
Linear Polarization ◽  
Wavelength Dependence ◽  
Position Angle ◽  
Orbital Inclination ◽  
V Band ◽  
Highly Active ◽  
Phase Interval ◽  
In The Beginning ◽  
Bright Phase

AbstractObservations of linear and circular polarization in five colour bands during a highly active state of VV Puppis in January 86 are reported. A strong linear polarization pulse with the maximum in the blue, PB ≈ 22%, is observed at the end of the bright phase when the active pole is at the limb and a weaker secondary pulse, PB ≈ 7%, is seen in the beginning of the bright phase, when the active pole reappears. Strong positive circular polarization is also observed in the blue and the ultraviolet, РU ≈ PB ≈ 18%, PV ≈ 10% during the bright phase. The circular polarization reverses the sign in the B and V bands during the faint phase and a negative polarization hump is seen when the active pole crosses the limb. The circular polarization in the V band reaches the value PV ≈ −10% at the hump, after which it remains near PV ≈ −5% during the faint phase. This is probably due to radiation coming from the second, less active pole and accretion thus takes place onto both poles. The wavelength dependences of the positive and negative parts of the circular polarization curve are different and no polarization reversal is seen in the U band. The position angle of the linear polarization is well determined during a large portion of the cycle, especially in the V band, thanks to the activity from both poles. A best fit to the position angle curve, taking into account also the duration of the positive circular polarization phase interval ΔΦ = 0.40 (in the V band), yields the values of orbital inclination i = 78° ± 2° and the colatitude of the active magnetic pole ß = 146° ± 2°. The relatively good fit to the position angle data indicates that the simple dipole model is nearly correct in the case of VV Puppis. Some wavelength dependence is, however, seen in the position angle curves, especially in the I band where the slope Δθ/ΔΦ at the main pulse is considerably smaller than in the other bands. The shape of the position angle curves changes also in the blue and the ultraviolet around the middle of the bright phase. This is probably due to optical thickness effects as the side of the accretion column which is toward the observer changes near this phase.

scholarly journals Symmetric Parsec-Scale Radio Jets in NGC 4261

1998 ◽  
Vol 164 ◽  
pp. 63-64
Author(s):  
Dayton L. Jones ◽  
Ann E. Wehrle
Keyword(s):  
Accretion Disk ◽  
Rotation Axis ◽  
Position Angle ◽  
Narrow Gap ◽  
Apparent Rotation ◽  
Radio Jets

AbstractVLBA observations of NGC 4261 (3C 270) reveal highly symmetric radio structures at both 1.6 and 8.4 GHz. There is little evidence for free-free absorption in the inner few pc, despite the fact that HST imaging shows this galaxy to contain a nearly edge-on disk of gas and dust in its nucleus. However, at our highest resolution we find a narrow gap in emission just east of the radio core which we interpret as evidence for a small (sub-parsec) nearly edge-on accretion disk which is obscuring the base of the counterjet. The position angle of the pc-scale radio axis agrees with the position angle of the VLA-scale jets, which differs from the apparent rotation axis of the nuclear disk seen by HST.

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 Direct Imaging of Planet Transit Events

2012 ◽  
Vol 8 (S293) ◽  
pp. 378-381
Author(s):  
Gerard T. van Belle ◽  
Kaspar von Braun ◽  
Tabetha Boyajian ◽  
Gail Schaefer
Keyword(s):  
Wavelength Dependence ◽  
Position Angle ◽  
Atmospheric Composition ◽  
Optical Interferometer ◽  
Direct Imaging ◽  
Stellar Radius ◽  
System Parameters ◽  
Optical Interferometers ◽  
Host Stars

AbstractExoplanet transit events are attractive targets for the ultrahigh-resolution capabilities afforded by optical interferometers. The intersection of two developments in astronomy enable direct imaging of exoplanet transits: first, improvements in sensitivity and precision of interferometric instrumentation; and second, identification of ever-brighter host stars. Efforts are underway for the first direct high-precision detection of closure phase signatures with the CHARA Array and Navy Precision Optical Interferometer. When successful, these measurements will enable recovery of the transit position angle on the sky, along with characterization of other system parameters, such as stellar radius, planet radius, and other parameters of the transit event. This technique can directly determine the planet's radius independent of any outside observations, and appears able to improve substantially upon other determinations of that radius; it will be possible to extract wavelength dependence of that radius determination, for connection to characterization of planetary atmospheric composition & structure. Additional directly observed parameters - also not dependent on transit photometry or spectroscopy - include impact parameter, transit ingress time, and transit velocity.

Sign in / Sign up

Export Citation Format

Share Document