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914 results on '"Circumstellar disk"'

1. Spectral Classification of Embedded Stars

Author

André, Philippe, Gargaud, Muriel, editor, Irvine, William M., editor, Amils, Ricardo, editor, Claeys, Philippe, editor, Cleaves, Henderson James, editor, Gerin, Maryvonne, editor, Rouan, Daniel, editor, Spohn, Tilman, editor, Tirard, Stéphane, editor, and Viso, Michel, editor

Published
2023
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2. GRMHD simulations of accretion flows onto massive binary black hole mergers embedded in a thin slab of gas

Author

Fedrigo, G, Cattorini, F, Giacomazzo, B, Colpi, M, Fedrigo G., Cattorini F., Giacomazzo B., Colpi M., Fedrigo, G, Cattorini, F, Giacomazzo, B, Colpi, M, Fedrigo G., Cattorini F., Giacomazzo B., and Colpi M.

Abstract

We present general relativistic magnetohydrodynamic simulations of merging equal-mass spinning black holes embedded in an equatorial thin slab of magnetized gas. We explore configurations with black holes that are nonspinning, with spins aligned to the orbital angular momentum, and with misaligned spins. The rest-mass density of the gas slab follows a Gaussian profile symmetric relative to the equatorial plane and it is initially either stationary or with Keplerian rotational support. As part of our diagnostics, we track the accretion of matter onto the black hole horizons and the Poynting luminosity. Throughout the inspiral phase, configurations with nonzero spins display modulations in the mass accretion rate that are proportional to the orbital frequency and its multiples. Frequency analysis suggests that these modulations are a generic feature of inflows on merging binaries. In contrast to binary models evolved in a gas cloud scenario, we do not observe a significant increase in the mass accretion rate after the merger in any of our simulations, suggesting the possibility of not detecting a peak luminosity at the time of merger in future electromagnetic observations.

Published
2024

3. Circumstellar Disk

Author

Gargaud, Muriel, editor, Irvine, William M., editor, Amils, Ricardo, editor, Claeys, Philippe, editor, Cleaves, Henderson James, editor, Gerin, Maryvonne, editor, Rouan, Daniel, editor, Spohn, Tilman, editor, Tirard, Stéphane, editor, and Viso, Michel, editor

Published
2023
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7. Spectral Classification of Embedded Stars

Author

André, Philippe, Gargaud, Muriel, editor, Irvine, William M., editor, Amils, Ricardo, editor, Cleaves, Henderson James (Jim), II, editor, Pinti, Daniele L., editor, Quintanilla, José Cernicharo, editor, Rouan, Daniel, editor, Spohn, Tilman, editor, Tirard, Stéphane, editor, and Viso, Michel, editor

Published
2015
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9. Optical and Near-Infrared Monitoring of Gamma-ray Binaries Hosting Be Stars

Author

Yuki Moritani and Akiko Kawachi

Subjects
gamma-ray binaries, optical and near-infrared, Be stars, circumstellar disk, gamma-ray binaries—individual (PSR B1259−63, LSI+61 303, HESS J0632+057), Elementary particle physics, QC793-793.5
Abstract

Optical and near-infrared observations are compiled for the three gamma-ray binaries hosting Be stars: PSR B1259−63, LSI+61 303, and HESS J0632+057. The emissions from the Be disk are considered to vary according to the changes in its structure, some of which are caused by interactions with the compact object (e.g., tidal forces). Due to the high eccentricity and large orbit of these systems, the interactions—and, hence the resultant observables—depend on the orbital phase. To explore such variations, multi-band photometry and linear polarization were monitored for the three considered systems, using two 1.5 m-class telescopes: IRSF at the South African Astronomical Observatory and Kanata at the Higashi–Hiroshima Observatory.

Published
2021
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12. Simulation of a Hydrodynamic Stellar Wind from a Rapidly Rotating Star.

Author

Bogovalov, S. V., Romanikhin, S. M., and Tronin, I. V.

Subjects
*STELLAR winds, *STELLAR rotation, *REYNOLDS number, *STELLAR mass, *SURFACE temperature, *STARS
Abstract

The mechanism for the formation of disk-like flows from rapidly rotating Be stars is not yet clear. An axisymmetric hydrodynamic stellar wind flow from a rapidly rotating star has been simulated numerically as a step in solving this problem. The change in the shape of the star as it rotates and the turbulence excited in the stellar wind at Reynolds numbers ∼109−1013 are taken into account. Calculations show the formation of a disk-like flow from the stellar surface at the equator, which expands into the polar regions due to a pressure gradient on scales of the order of the stellar radius. A poloidal velocity vortex is formed at high latitudes. No turbulence is excited near the equator within the simplest standard models and, therefore, no quasi-Keplerian disk-like flow emerges in the equatorial plane. A dependence of the total mass flux on the stellar rotation rate at various surface temperatures has been obtained. [ABSTRACT FROM AUTHOR]

Published
2019
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22. An Unbiased Mineral Compositional Analysis Technique for Circumstellar Disks

Author

Yung Kipreos and Inseok Song

Subjects
Mineral, Materials science, General Medicine, Astrophysics, Circumstellar disk
Abstract

A circumstellar disk that surrounds a star is composed of gas, dust, and rocky objects that are in orbit around it. Around infant stars, this disk can act as a source of material that can be used to form planetesimals, which can then accrete more material and form into planets. Studying the mineral composition of these disks can provide insight into the processes that created our solar system. The purpose of this paper is to analyze the mineral composition of these disks by using a newly created python package, Min-CaLM. This package determines the relative mineral abundance within a disk by using a linear regression technique called non-negative least square minimization. The circumstellar disks that are capable of undergoing compositional analysis must have a spectrum with both a detectable mid-infrared excess and prominent silicate features. From our sample, there are only eight debris disks that qualify to be candidates for the Min-CaLM program. The mineral compositions calculated by Min-CaLM are then compared to the Tholen asteroid classification scheme. HD 23514, HD 105234, HD 15407A, BD+20 307, HD 69830, and HD 172555 are found to have a compositions similar to that expected for C-type asteroids, TYC 9410-532-1 resembles the composition of S-type asteroids, and HD 100546 resembles D-type asteroids. Min-CaLM also calculates the mineral compositions of the comets Tempel 1 and Hale-Bopp, and they are used as a comparison between the material in our early solar system and the debris disk compositions. KEYWORDS: Debris disk; Mineral; Composition; Analysis; Asteroid; Circumstellar; Spectroscopy; Python

Published
2021

25. A sub-AU study of CI Tau with GRAVITY: The key to connect Stars, Disks and Planets

Author

Soulain, Anthony, Bouvier, Jérôme, Perraut, Karine, Tessore, Benjamin, Brun, Allan Sacha, Bouvier, Jérôme, and Petit, Pascal

Subjects
Magnetosphere, Circumstellar disk, Stars
Abstract

For a few million years after the gravitational collapse that led to their formation; young stellar systems remain surrounded by a circumstellar disk from which planets form. ALMA and VLT/SPHERE have provided spectacular images of the planet-forming disks on a scale of a few 10 au (Garufi et al. 2017) and; even more recently; led to the direct detection of forming planets within the disk (Benisty et al. 2021). In contrast; the exploration of the innermost disk regions (≲ 1 au) has remained quite challenging so far. Moreover; the Kepler satellite has revealed that the most ubiquitous planetary systems consist of compact strings of super-Earth and mini-Neptunes orbiting close to their host star (Porb ≲ 100 days; e.g.; Otegi et al. 2022;). It is; therefore; crucial to investigate the physics of the star-planet-inner disk interaction in young stars; not only for the role it plays in the early evolution of solar-type stars (e.g.; accretion/ejection; angular momentum; etc.) but also to determine the environmental conditions that prevail at the time of planetary formation. This is a necessary step towards understanding the formation of the plethora of compact inner low-mass planetary systems observed across the Galaxy. CI Tau is so far the only pre-main sequence star still accreting from its surrounding disk (classical T-Tauri star) claimed to host a hot Jupiter planet. However; the periodic radial velocity variation could result from magnetospheric accretion onto the star rather than from an orbiting body (Donati et al. 2020). The most interesting aspect of CI Tau regards its extreme magnetic field (3.7 kG) that disrupts the inner gaseous disk and generates accretion funnel flows down to the stellar surface. We propose to present our investigation about the inner region of CI Tau; aiming at reconnecting the different spatial scales of the system down to a few stellar radii (≲ 0.1 AU). Method: We investigated this puzzling question using the long-baseline interferometry technique; the only way to probe the inner region of the system at sub-AU precision. Thanks to the high spectral resolution of VLTI/GRAVITY (R=4000); we are both sensitive to the emitting dusty part of the inner rim (K-band continuum); and the magnetosphere itself traced by the Brγ emission line. Results: In the continuum; we characterise the disk's inner rim; which appeared to be disconnected from the outer disk with a large misalignment both in inclination and position angle. We report an internal rim position at 0.20 ± 0.02 AU; remarkably more significant than the theoretical sublimation radius of 0.03-0.06 AU. Such difference could infer the presence of a planet carving the inner part of the disk; as recently supported by hydrodynamical simulation (Muley et al. 2021). The non-zero closure phases measured by GRAVITY suggest an important asymmetry in the disk: the southwest side appears brighter than the northeast. Such difference argues in favour of an inclined disk where the brilliant (and farthest) part is seen from the bottom (distant observer point of view). We confirmed such behaviours using radiative transfer modelling with RADMC3d. In the Brγ line (2.1661 μm), our model suggests a bright but smaller emitting region than the thermal emission with a radius of 0.05 ± 0.01 AU (4 times smaller than the inner rim). Such characteristic is strongly supported by the magnetosphere accreting models developed in our team and will be presented for comparison. Conclusion: With GRAVITY; we characterise the inner disk of CI Tau with a sub-AU precision; allowing a direct comparison with the standard YSO's characteristic sizes such as sublimation; co-rotation or magnetic truncation radii. The existence of a larger than expected central cavity could be an observational signature of the well known 11.6 Mj planet (CI Tau b). The substantially detected misalignment between inner and outer disks constitutes a challenge for the modelling efforts and should be carefully investigated in the future., {"references":["Donati, J.-F. et al. (2019), MNRAS, 491, 5660-5670","Gravity Collaboration, Abuter, R. et. al (2017), A&A, 602, A94","Lazareff, B. et al. (2017), A&A, 599, A85","Gravity Collaboration, Perraut, K. et. al (2021), A&A, 655, A73","Bouvier, J. et al. (2017), A&A, 636, A108"]}

Published
2022
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32. The James Webb Space Telescope

Author

Gardner, Jonathan P, Mather, John C., Clampin, Mark, Doyon, Rene, Flanagan, Kathryn A., Franx, Marijn, Greenhouse, Matthew A., Hammel, Heidi B., Hutchings, John B., Jakobsen, Peter, Lilly, Simon J., Lunine, Jonathan I., McCaughrean, Mark J., Mountain, Matt, Rieke, George H., Rieke, Marcia J., Sonneborn, George, Stiavelli, Massimo, Windhorst, Rogier, Wright., Gillian S., Burton, W.B., editor, Christensen, Lars Lindberg, editor, Thronson, Harley A., editor, Stiavelli, Massimo, editor, and Tielens, Alexander, editor

Published
2009
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35. (Sub)mm Interferometry Applications in Star Formation Research

Author

Beuther, H., Beig, R., editor, Beiglböck, W., editor, Domcke, W., editor, Englert, B.-G., editor, Frisch, U., editor, Hänggi, P., editor, Hasinger, G., editor, Hepp, K., editor, Hillebrandt, W., editor, Imboden, D., editor, Jaffe, R. L., editor, Lipowsky, R., editor, Löhneysen, H.v., editor, Ojima, I., editor, Sornette, D., editor, Theisen, S., editor, Weise, W., editor, Wess, J., editor, Zittartz, J., editor, Bacciotti, Francesca, editor, Testi, Leonardo, editor, and Whelan, Emma, editor

Published
2008
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36. Observations of YSO Jets from Space: HST and Beyond

Author

Bacciotti, F., McCaughrean, M., Ray, T., Beig, R., editor, Beiglböck, W., editor, Domcke, W., editor, Englert, B.-G., editor, Frisch, U., editor, Hänggi, P., editor, Hasinger, G., editor, Hepp, K., editor, Hillebrandt, W., editor, Imboden, D., editor, Jaffe, R. L., editor, Lipowsky, R., editor, Löhneysen, H.v., editor, Ojima, I., editor, Sornette, D., editor, Theisen, S., editor, Weise, W., editor, Wess, J., editor, Zittartz, J., editor, Bacciotti, Francesca, editor, Testi, Leonardo, editor, and Whelan, Emma, editor

Published
2008
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39. Near-Infrared Fiber Imager for the VLTI

Author

Neuhäuser, Ralph, Tünnermann, Andreas, Hempel, Marc, Stecklum, Bringfried, Ruske, Jena-Peter, Guenther, Eike, Hatzes, Artie, Chini, Rolf, Lemke, Roland, Wuchterl, Günther, Lühe, Oskar von der, Leibundgut, Bruno, editor, Richichi, A., editor, Delplancke, F., editor, Paresce, F., editor, and Chelli, A., editor

Published
2008
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43. FU Orionis - The MIDI Perspective

Author

Quanz, Sascha P., Henning, Thomas, Leinert, Christoph, Ratzka, Thorsten, Wolf, Sebastian, Leibundgut, Bruno, editor, Richichi, A., editor, Delplancke, F., editor, Paresce, F., editor, and Chelli, A., editor

Published
2008
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48. Multiwavelength Vertical Structure in the AU Mic Debris Disk:Characterizing the Collisional Cascade

Author

Vizgan, David, Hughes, A. Meredith, Carter, Evan S., Flaherty, Kevin M., Pan, Margaret, Chiang, Eugene, Schlichting, Hilke, Wilner, David J., Andrews, Sean M., Carpenter, John M., Moor, Attila, MacGregor, Meredith A., Vizgan, David, Hughes, A. Meredith, Carter, Evan S., Flaherty, Kevin M., Pan, Margaret, Chiang, Eugene, Schlichting, Hilke, Wilner, David J., Andrews, Sean M., Carpenter, John M., Moor, Attila, and MacGregor, Meredith A.

Abstract

Debris disks are scaled-up analogs of the Kuiper Belt in which dust is generated by collisions between planetesimals. In the collisional cascade model of debris disks, the dust lost to radiation pressure and winds is constantly replenished by grinding collisions between planetesimals. The model assumes that collisions are destructive and involve large velocities; this assumption has not been tested beyond our solar system. We present 0.'' 25 (approximate to 2.4 au) resolution observations of the lambda = 450 mu m dust continuum emission from the debris disk around the nearby M dwarf AU Microscopii with the Atacama Large Millimeter/submillimeter Array. We use parametric models to describe the disk structure, and a Monte Carlo Markov Chain (MCMC) algorithm to explore the posterior distributions of the model parameters; we fit the structure of the disk to both our data and archival lambda = 1.3 mm data (Daley et al. 2019), from which we obtain two aspect ratio measurements at 1.3 mm (h(1300) = 0.025(-0.002)(+0.008)) and at 450 mu m (h(450) = 0.019(-0.001)(+0.006)), as well as the grain-size distribution index q = 3.03 +/- 0.02. Contextualizing our aspect ratio measurements within the modeling framework laid out in Pan & Schlichting (2012), we derive a power-law index of velocity dispersion as a function of grain size p = 0.28 +/- 0.06 for the AU Mic debris disk. This result implies that smaller bodies are more easily disrupted than larger bodies by collisions, which is inconsistent with the strength regime usually assumed for such small bodies. Possible explanations for this discrepancy are discussed.

Published
2022

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