4
4.0
-
-
-
by
R. Lombaert; L. Decin; P. Royer; A. de Koter; N. L. J. Cox; E. González-Alfonso; D. Neufeld; J. De Ridder; M. Agúndez; J. A. D. L. Blommaert; T. Khouri; M. A. T. Groenewegen; F. Kerschbaum; J. Cernicharo; B. Vandenbussche; C. Waelkens
texts
eye 4
favorite 0
comment 0
Context. The recent detection of warm H$_2$O vapor emission from the outflows of carbon-rich asymptotic giant branch (AGB) stars challenges the current understanding of circumstellar chemistry. Two mechanisms have been invoked to explain warm H$_2$O vapor formation. In the first, periodic shocks passing through the medium immediately above the stellar surface lead to H$_2$O formation. In the second, penetration of ultraviolet interstellar radiation through a clumpy circumstellar medium leads to...
Topics: Astrophysics, Solar and Stellar Astrophysics, Astrophysics of Galaxies
Source: http://arxiv.org/abs/1601.07017
11
11
-
-
-
by
E. O'Gorman; W. Vlemmings; A. M. S. Richards; A. Baudry; E. De Beck; L. Decin; G. M. Harper; E. M. Humphreys; P. Kervella; T. Khouri; S. Muller
texts
eye 11
favorite 0
comment 0
The processes leading to dust formation and the subsequent role it plays in driving mass loss in cool evolved stars is an area of intense study. Here we present high resolution ALMA Science Verification data of the continuum emission around the highly evolved oxygen-rich red supergiant VY CMa. These data enable us to study the dust in its inner circumstellar environment at a spatial resolution of 129 mas at 321 GHz and 59 mas at 658 GHz, thus allowing us to trace dust on spatial scales down to...
Topics: Astrophysics, Solar and Stellar Astrophysics
Source: http://arxiv.org/abs/1410.1622
4
4.0
-
-
-
by
T. Khouri; U. Zeitler; C. Reichl; W. Wegscheider; N. E. Hussey; S. Wiedmann; J. C. Maan
texts
eye 4
favorite 0
comment 0
We report a magnetotransport study of an ultra-high mobility ($\bar{\mu}\approx 25\times 10^6$\,cm$^2$\,V$^{-1}$\,s$^{-1}$) $n$-type GaAs quantum well up to 33 T. A strong linear magnetoresistance (LMR) of the order of 10$^5$ % is observed in a wide temperature range between 0.3 K and 60 K. The simplicity of our material system with a single sub-band occupation and free electron dispersion rules out most complicated mechanisms that could give rise to the observed LMR. At low temperature,...
Topics: Mesoscale and Nanoscale Physics, Condensed Matter
Source: http://arxiv.org/abs/1611.04857
5
5.0
-
-
-
by
T. Khouri; W. H. T. Vlemmings; S. Ramstedt; R. Lombaert; M. Maercker; E. De Beck
texts
eye 5
favorite 0
comment 0
We report the serendipitous detection with ALMA of the vibrationally-excited pure-rotational CO transition $v=1, J=3-2$ towards five asymptotic giant branch (AGB) stars, $o$ Cet, R Aqr, R Scl, W Aql, and $\pi^1$ Gru. The observed lines are formed in the poorly-understood region located between the stellar surface and the region where the wind starts, the so-called warm molecular layer. We successfully reproduce the observed lines profiles using a simple model. We constrain the extents,...
Topics: Astrophysics, Solar and Stellar Astrophysics
Source: http://arxiv.org/abs/1608.03271
6
6.0
-
-
-
by
T. Khouri; M. Maercker; L. B. F. M. Waters; W. H. T. Vlemmings; P. Kervella; A. de Koter; C. Ginski; E. De Beck; L. Decin; M. Min; C. Dominik; E. O'Gorman; H. -M. Schmid; R. Lombaert; E. Lagadec
texts
eye 6
favorite 0
comment 0
We use high-angular-resolution images obtained with SPHERE/ZIMPOL to study the photosphere, the warm molecular layer, and the inner wind of the close-by oxygen-rich AGB star R Doradus. We present observations in filters V, cntH$\alpha$, and cnt820 and investigate the surface brightness distribution of the star and of the polarised light produced in the inner envelope. Thanks to second-epoch observations in cntH$\alpha$, we are able to see variability on the stellar photosphere. We find that in...
Topics: Astrophysics, Solar and Stellar Astrophysics
Source: http://arxiv.org/abs/1605.05504
9
9.0
-
-
-
by
T. Khouri; A. de Koter; L. Decin; L. B. F. M. Waters; M. Maercker; R. Lombaert; J. Alcolea; J. A. D. L. Blommaert; V. Bujarrabal; M. A. T. Groenewegen; K. Justtanont; F. Kerschbaum; M. Matsuura; K. M. Menten; H. Olofsson; P. Planesas; P. Royer; M. R. Schmidt; R. Szczerba; D. Teyssier; J. Yates
texts
eye 9
favorite 0
comment 0
The evolution of low- and intermediate-mass stars on the asymptotic giant branch (AGB) is mainly controlled by the rate at which these stars lose mass in a stellar wind. Understanding the driving mechanism and strength of the stellar winds of AGB stars and the processes enriching their surfaces with products of nucleosynthesis are paramount to constraining AGB evolution and predicting the chemical evolution of galaxies. In a previous paper we have constrained the structure of the outflowing...
Topics: Astrophysics, Solar and Stellar Astrophysics
Source: http://arxiv.org/abs/1409.0396
17
17
-
-
-
by
T. Khouri; L. B. F. M. Waters; A. de Koter; L. Decin; M. Min; B. L. de Vries; R. Lombaert; N. L. J. Cox
texts
eye 17
favorite 0
comment 0
Low- and intermediate-mass stars go through a period of intense mass-loss at the end of their lives in a phase known as the asymptotic giant branch (AGB). During the AGB a significant fraction of their initial mass is expelled in a stellar wind. This process controls the final stages of their evolution and contributes to the chemical evolution of galaxies. However, the wind-driving mechanism of AGB stars is not yet well understood, especially so for oxygen-rich sources. Characterizing both the...
Topics: Solar and Stellar Astrophysics, Astrophysics
Source: http://arxiv.org/abs/1503.04765
43
43
-
-
-
by
J. Cernicharo; L. B. F. M. Waters; L. Decin; P. Encrenaz; A. G. G. M. Tielens; M. Agundez; E. De Beck; H. S. P. Muller; J. R. Goicoechea; M. J. Barlow; A. Benz; N. Crimier; F. Daniel; A. M. Di Giorgio; M. Fich; T. Gaier; P. Garcia-Lario; A. De Koter; T. Khouri; R. Liseau; R. Lombaert; N. Erickson; J. R. Pardo; J. C. Pearson; R. Shipman; C. Sanchez-Contreras; D. Teyssier
texts
eye 43
favorite 0
comment 0
We present the first results of a high-spectral-resolution survey of the carbon-rich evolved star IRC+10216 that was carried out with the HIFI spectrometer onboard Herschel. This survey covers all HIFI bands, with a spectral range from 488 to 1901GHz. In this letter we focus on the band-1b spectrum, in a spectral range 554.5-636.5GHz, where we identified 130 spectral features with intensities above 0.03 K and a signal-to-noise ratio >5. Detected lines arise from HCN, SiO, SiS, CS, CO,...
Source: http://arxiv.org/abs/1008.1199v1
5
5.0
-
-
-
by
T. Khouri; A. de Koter; L. Decin; L. B. F. M. Waters; R. Lombaert; P. Royer; B. Swinyard; M. J. Barlow; J. Alcolea; J. A. D. L. Blommaert; V. Bujarrabal; J. Cernicharo; M. A. T. Groenewegen; K. Justtanont; F. Kerschbaum; M. Maercker; A. Marston; M. Matsuura; G. Melnick; K. M. Menten; H. Olofsson; P. Planesas; E. Polehampton; Th. Posch; M. Schmidt; R. Szczerba; B. Vandenbussche; J. Yates
texts
eye 5
favorite 0
comment 0
Asymptotic giant branch (AGB) stars lose their envelopes by means of a stellar wind whose driving mechanism is not understood well. Characterizing the composition and thermal and dynamical structure of the outflow provides constraints that are essential for understanding AGB evolution, including the rate of mass loss and isotopic ratios. We modeled the CO emission from the wind of the low mass-loss rate oxygen-rich AGB star W Hya using data obtained by the HIFI, PACS, and SPIRE instruments...
Topics: Astrophysics, Solar and Stellar Astrophysics
Source: http://arxiv.org/abs/1403.2892
14
14
-
-
-
by
R. Lombaert; L. Decin; A. de Koter; J. A. D. L. Blommaert; P. Royer; E. De Beck; B. L. de Vries; T. Khouri; M. Min
texts
eye 14
favorite 0
comment 0
Context: AGB stars lose a large percentage of their mass in a dust-driven wind. This creates a circumstellar envelope, which can be studied through thermal dust emission and molecular emission lines. In the case of high mass-loss rates, this study is complicated by the high optical depths and the intricate coupling between gas and dust radiative transfer characteristics. An important aspect of the physics of gas-dust interactions is the strong influence of dust on the excitation of several...
Topics: Solar and Stellar Astrophysics, Astrophysics
Source: http://arxiv.org/abs/1505.07696
3
3.0
-
-
-
by
L. Decin; A. M. S. Richards; L. B. F. M. Waters; T. Danilovich; D. Gobrecht; T. Khouri; W. Homan; J. Bakker; M. Van de Sande; J. A. Nuth; E. De Beck
texts
eye 3
favorite 0
comment 0
(abbreviated) We aim to constrain the dust formation histories in the winds of oxygen-rich AGB stars. We have obtained ALMA observations with a spatial resolution of 120x150 mas tracing the dust formation region of a low mass-loss rate and a high mass-loss rate AGB star, R Dor and IK Tau. Emission line profiles of AlO, AlOH and AlCl are detected and are used to derive a lower limit of atomic aluminium incorporated in molecules. We show that the gas-phase aluminium chemistry is completely...
Topics: Solar and Stellar Astrophysics, Astrophysics
Source: http://arxiv.org/abs/1704.05237
4
4.0
-
-
-
by
S. Wiedmann; A. Jost; B. Fauque; J. van Dijk; M. J. Meijer; T. Khouri; S. Pezzini; S. Grauer; S. Schreyeck; C. Brune; H. Buhmann; L. W. Molenkamp; N. E. Hussey
texts
eye 4
favorite 0
comment 0
We report on high-field angle-dependent magneto-transport measurements on epitaxial thin films of Bi2Se3, a three-dimensional topological insulator. At low temperature, we observe quantum oscillations that demonstrate the simultaneous presence of bulk and surface carriers. The magneto- resistance of Bi2Se3 is found to be highly anisotropic. In the presence of a parallel electric and magnetic field, we observe a strong negative longitudinal magneto-resistance that has been consid- ered as a...
Topics: Mesoscale and Nanoscale Physics, Condensed Matter
Source: http://arxiv.org/abs/1608.03615
47
47
-
-
-
by
K. Justtanont; T. Khouri; M. Maercker; J. Alcolea; L. Decin; H. Olofsson; A. P. Marston; D. Teyssier; J. Cernicharo; C. Dominik; A. de Koter; G. Melnick; K. M. Menten; D. Neufeld; P. Planesas; M. Schmidt; R. Szczerba; R. Waters
texts
eye 47
favorite 0
comment 0
Spectra, taken with the heterodyne instrument, HIFI, aboard the Herschel Space Observatory, of O-rich asymptotic giant branch (AGB) stars which form part of the guaranteed time key program HIFISTARS are presented. The aim of this program is to study the dynamical structure, mass-loss driving mechanism, and chemistry of the outflows from AGB stars as a function of chemical composition and initial mass. We used the HIFI instrument to observe nine AGB stars, mainly in the H2O and high rotational...
Source: http://arxiv.org/abs/1111.5156v1
6
6.0
-
-
-
by
T. Khouri; M. Bendias; P. Leubner; C. Brüne; H. Buhmann; L. W. Molenkamp; U. Zeitler; N. E. Hussey; S. Wiedmann
texts
eye 6
favorite 0
comment 0
We report on the observation of the quantum Hall effect at high temperatures in HgTe quantum wells with a finite band gap and a thickness below and above the critical thickness $d_\textnormal{c}$ that separates a conventional semiconductor from a two-dimensional topological insulator. At high carrier concentrations we observe a quantized Hall conductivity up to 60\,K with energy gaps between Landau Levels of the order of 25\,meV, in good agreement with the Landau Level spectrum obtained from...
Topics: Mesoscale and Nanoscale Physics, Condensed Matter
Source: http://arxiv.org/abs/1605.03342
