Two-Dimensional Hydrodynamical Simulations of Wind-Compressed Disks Around Rapidly Rotating B-Stars

In high-mass microquasars (HMMQ), strong interactions between jets and stellar winds at binary system scales could occur. In order to explore this possibility, we have performed numerical two-dimensional hydrodynamical simulations of jets crossing the dense stellar material to study how the jet will be affected by these interactions. We find that the jet head generates strong shocks in the wind. These shocks reduce the jet advance speed, and compress and heat up the jet and wind material. In addition, strong recollimation shocks can occur where pressure balance between the jet side and the surrounding medium is reached. All this, together with jet bending, could lead to the destruction of jets with power < 1036 erg/s . The conditions around the outflow shocks would be convenient for accelerating particles up to ~ TeV energies. These accelerated particles could emit via synchrotron and inverse Compton (IC) scattering if they were leptons, and via hadronic processes if they were hadrons.

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Hydrodynamical simulations of the barred spiral galaxy NGC 1097

Proceedings of the International Astronomical Union ◽

10.1017/s174392131401148x ◽

2012 ◽

Vol 10 (H16) ◽

pp. 376-376

Author(s):

Lien-Hsuan Lin ◽

Hsiang-Hsu Wang ◽

Pei-Ying Hsieh ◽

Ronald E. Taam ◽

Chao-Chin Yang ◽

...

Keyword(s):

Spiral Galaxy ◽

Gas Flow ◽

Elliptical Galaxy ◽

The Self ◽

Two Dimensional ◽

Nuclear Ring ◽

Barred Spiral Galaxy ◽

Circumnuclear Disk ◽

Hydrodynamical Simulations ◽

Self Gravity

AbstractNGC 1097 is a nearby barred spiral galaxy believed to be interacting with the elliptical galaxy NGC 1097A located to its northwest. It hosts a Seyfert 1 nucleus surrounded by a circumnuclear starburst ring. Two straight dust lanes connected to the ring extend almost continuously out to the bar. The other ends of the dust lanes attach to two main spiral arms. To provide a physical understanding of its structural and kinematical properties, two-dimensional hydrodynamical simulations have been carried out. Numerical calculations reveal that many features of the gas morphology and kinematics can be reproduced provided that the gas flow is governed by a gravitational potential associated with a slowly rotating strong bar. By including the self-gravity of the gas disk in our calculation, we have found the starburst ring to be gravitationally unstable which is consistent with the observation in Hsieh et al. (2011). Our simulations also show that gas can flow into the region within the starburst ring even after its formation, leading to the coexistence of both a nuclear ring and a circumnuclear disk.

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Ultraviolet Spectrophotometry of Early-Type Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900008925 ◽

1976 ◽

Vol 72 ◽

pp. 161-165 ◽

Cited By ~ 3

Author(s):

K. Nandy ◽

G. I. Thompson ◽

C. M. Humphries

Keyword(s):

Classification Scheme ◽

Narrow Band ◽

Two Dimensional ◽

Early Type ◽

Ultraviolet Spectrophotometry ◽

B Stars ◽

Preliminary Results ◽

Ultraviolet Spectra ◽

Dimensional Classification ◽

Early Type Stars

The ultraviolet spectra of B stars obtained with the sky scan telescope in the TD1 satellite have been used to obtain narrow-band magnitudes at several wavelengths. These photometric bands have an effective half-width of 100 Å. We have proposed a two-dimensional classification scheme based on ultraviolet colours, and some preliminary results are presented.

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Migration of planets in circumbinary discs

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832804 ◽

2018 ◽

Vol 616 ◽

pp. A47 ◽

Cited By ~ 14

Author(s):

Daniel Thun ◽

Wilhelm Kley

Keyword(s):

Binary Stars ◽

Special Focus ◽

Two Dimensional ◽

Mass Ratio ◽

Orbital Elements ◽

Lower Mass ◽

Orbital Parameters ◽

Current Location ◽

Hydrodynamical Simulations ◽

Grid Based

Aims. The discovery of planets in close orbits around binary stars raises questions about their formation. It is believed that these planets formed in the outer regions of the disc and then migrated through planet-disc interaction to their current location. Considering five different systems (Kepler-16, -34, -35, -38, and -413) we model planet migration through the disc, with special focus on the final orbital elements of the planets. We investigate how the final orbital parameters are influenced by the disc and planet masses. Methods. Using two-dimensional, locally isothermal, and viscous hydrodynamical simulations, we first model the disc dynamics for all five systems, followed by a study of the migration properties of embedded planets with different masses. To strengthen our results, we apply two grid-based hydrodynamical codes using different numerics (PLUTO and FARGO3D). Results. For all systems, we find that the discs become eccentric and precess slowly. We confirm the bifurcation feature in the precession period – gap-size diagram for different binary mass ratios. The Kepler-16, -35, -38, and -413 systems lie on the lower branch and Kepler-34 on the upper one. For systems with small binary eccentricity, we find a new non-monotonic, loop-like feature. In all systems, the planets migrate to the inner edge of the disc cavity. Depending on the planet-disc mass ratio, we observe one of two different regimes. Massive planets can significantly alter the disc structure by compressing and circularising the inner cavity and they remain on nearly circular orbits. Lower-mass planets are strongly influenced by the disc, their eccentricity is excited to high values, and their orbits are aligned with the inner disc in a state of apsidal corotation. In our simulations, the final locations of the planets are typically too large with respect to the observations because of the large inner gaps of the discs. The migrating planets in the most eccentric discs (around Kepler-34 and -413) show the largest final eccentricity in agreement with the observations.

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Two-dimensional hydrodynamical simulations of wind-compressed disks around rapidly rotating B-stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900215647 ◽

1994 ◽

Vol 162 ◽

pp. 469-469 ◽

Cited By ~ 1

Author(s):

S. P. Owocki ◽

S. R. Cranmer ◽

J. M. Blondin

Keyword(s):

Simple Model ◽

Circumstellar Disks ◽

Rotating Stars ◽

Disk Model ◽

B Stars ◽

Half Angle ◽

Be Star ◽

Dynamical Treatment ◽

Hydrodynamical Simulations ◽

Rapidly Rotating Stars

We use a 2-D PPM code to simulate numerically the hydrodynamics of a radiation-driven stellar wind from a rapidly rotating Be-star. The results generally confirm predictions of the semi-analytic “Wind Compressed Disk” model recently proposed by Bjorkman and Cassinelli to explain the circumstellar disks inferred observationally to exist around such rapidly rotating stars. However, this numerical simulation is able to incorporate several important effects not accounted for in the simple model, including a dynamical treatment of the outward radiative driving and gas pressure, as well as a rotationally oblated stellar surface. This enables us to model quantitatively the compressed wind and shock that forms the equatorial disk. The simulation results thus do differ in several important details from the simple model, showing, for example, cases of inner disk inflow not possible in the heuristic approach of assuming a fixed outward velocity law. In addition, the disk opening typically has a half-angle of 2–4 degrees, somewhat larger than the ~ 0.5° predicted from the analytic model, and there is no evidence for the predicted detachment of the disk that arises in the fixed outflow picture.

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Two-dimensional simulations of internal gravity waves in the radiation zones of intermediate-mass stars

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2296 ◽

2020 ◽

Vol 497 (4) ◽

pp. 4231-4245 ◽

Cited By ~ 1

Author(s):

R P Ratnasingam ◽

P V F Edelmann ◽

T M Rogers

Keyword(s):

Gravity Waves ◽

Internal Gravity Waves ◽

Two Dimensional ◽

Intermediate Mass ◽

Single Wave ◽

Linear Interaction ◽

Generation Spectrum ◽

Non Linear ◽

Hydrodynamical Simulations ◽

Spectrum Slope

ABSTRACT Intermediate-mass main-sequence stars have large radiative envelopes overlying convective cores. This configuration allows internal gravity waves (IGWs) generated at the convective–radiative interface to propagate towards the stellar surface. The signatures of these waves can be observed in the photometric and spectroscopic data from stars. We have studied the propagation of these IGWs using two-dimensional (2D) fully non-linear hydrodynamical simulations with realistic stellar reference states from the 1D stellar evolution code, Modules for Stellar Astrophysics (mesa). When a single wave is forced, we observe wave self-interaction. When two waves are forced, we observe non-linear interaction (i.e. triadic interaction) between these waves forming waves at different wavelengths and frequencies. When a spectrum of waves similar to that found in numerical simulations is forced, we find that the surface IGW frequency slope is consistent with recent observations. This power law is similar to that predicted by linear theory for the wave propagation, with small deviations that can be an effect of non-linearities. When the same generation spectrum is applied to 3 M⊙ models at different stellar rotation and ages, the surface IGW spectrum slope is very similar to the generation spectrum slope.

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Photo-electric Hβ and uvby photometry

Symposium - International Astronomical Union ◽

10.1017/s0074180900053407 ◽

1966 ◽

Vol 24 ◽

pp. 170-180

Author(s):

D. L. Crawford

Keyword(s):

Narrow Band ◽

Line Strength ◽

Interference Filter ◽

B Stars ◽

Relative Line ◽

The Mean ◽

F Stars ◽

Two Parameters ◽

Filter Photometry ◽

The Continuum

Early in the 1950's Strömgren (1, 2, 3, 4, 5) introduced medium to narrow-band interference filter photometry at the McDonald Observatory. He used six interference filters to obtain two parameters of astrophysical interest. These parameters he calledlandc, for line and continuum hydrogen absorption. The first measured empirically the absorption line strength of Hβby means of a filter of half width 35Å centered on Hβand compared to the mean of two filters situated in the continuum near Hβ. The second index measured empirically the Balmer discontinuity by means of a filter situated below the Balmer discontinuity and two above it. He showed that these two indices could accurately predict the spectral type and luminosity of both B stars and A and F stars. He later derived (6) an indexmfrom the same filters. This index was a measure of the relative line blanketing near 4100Å compared to two filters above 4500Å. These three indices confirmed earlier work by many people, including Lindblad and Becker. References to this earlier work and to the systems discussed today can be found in Strömgren's article inBasic Astronomical Data(7).

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Spectrophotometric measurements of objective-prism spectra

Symposium - International Astronomical Union ◽

10.1017/s007418090005333x ◽

1966 ◽

Vol 24 ◽

pp. 118-119

Author(s):

Th. Schmidt-Kaler

Keyword(s):

Progress Report ◽

Two Dimensional ◽

Objective Prism ◽

Made In

I should like to give you a very condensed progress report on some spectrophotometric measurements of objective-prism spectra made in collaboration with H. Leicher at Bonn. The procedure used is almost completely automatic. The measurements are made with the help of a semi-automatic fully digitized registering microphotometer constructed by Hög-Hamburg. The reductions are carried out with the aid of a number of interconnected programmes written for the computer IBM 7090, beginning with the output of the photometer in the form of punched cards and ending with the printing-out of the final two-dimensional classifications.

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