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1. HYDRODYNAMIC MODEL FOR A β Cephei VARIABLE BW Vulpeculae

Author

A. Fokin, Ph. Mathias, E. Chapellier, D. Gillet, and N. Nardetto

Subjects
Astronomy, QB1-991
Abstract

A hydrodynamical model for the high-amplitude β Cephei star BW Vulpeculae is generated, and the spectral line profiles are calculated for different pulsational phases. The pulsational characteristics and line profiles are compared with recent observational data obtained during seven consecutive nights in August 2000. We found a generally good agreement in the basic photometric and spectral parameters. Two strong shock waves appear during one period, and the "stillstand" is due to the gas dynamics between the passages of these shocks. Note that this good agreement suppose a metallicity Z=0.03, while a metallicity Z=0.02 does not lead to the correct amplitudes and shapes of the curves.

Published
2017
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2. Three-dimensional imaging of convective cells in the photosphere of Betelgeuse

Author

A. López Ariste, S. Georgiev, Ph. Mathias, A. Lèbre, M. Wavasseur, E. Josselin, R. Konstantinova-Antova, Th. Roudier, Institut de recherche en astrophysique et planétologie (IRAP), Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Centre National d'Études Spatiales [Toulouse] (CNES), Institute of Astronomy, Bulgarian Academy of Sciences, Sofia, Bulgaria, dinko@astro.bas.bg, Laboratoire Univers et Particules de Montpellier (LUPM), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo-France -Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Université Fédérale Toulouse Midi-Pyrénées-Centre National d'Études Spatiales [Toulouse] (CNES)-Météo-France -Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), and Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, stars: atmospheres, Astrophysics::Solar and Stellar Astrophysics, FOS: Physical sciences, supergiants, Astronomy and Astrophysics, [PHYS.ASTR.SR]Physics [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Solar and Stellar Astrophysics (astro-ph.SR)
Abstract

Understanding convection in red supergiants and the mechanisms that trigger the mass loss from these evolved stars are the general goals of most observations of Betelgeuse and its inner circumstellar environment. Linear spectropolarimetry of the atomic lines of the spectrum of Betelgeuse reveals information about the three-dimensional (3D) distribution of brightness in its atmosphere. We model the distribution of plasma and its velocities and use inversion algorithms to fit the observed linear polarization. We obtain the first 3D images of the photosphere of Betelgeuse. Within the limits of the used approximations, we recover vertical convective flows and measure the velocity of the rising plasma at different heights in the photosphere. In several cases, we find this velocity to be constant with height, indicating the presence of forces other than gravity acting on the plasma and counteracting it. In some cases, these forces are sufficient to maintain plasma rising at 60\,\kms to heights where this velocity is comparable to the escape velocity. Forces are present in the photosphere of Betelgeuse that allow plasma to reach velocities close to the escape velocity. These mechanisms may suffice to trigger mass loss and sustain the observed large stellar winds of these evolved stars., Comment: 15 pages, 10 figures. In press with A&A

Published
2022
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3. Pulsating chromosphere of classical Cepheids

Author

Andrea Chiavassa, Ph. Mathias, A. Mérand, Behnam Javanmardi, Eric Lagadec, Nancy Remage Evans, D. Gillet, V. Hocdé, Pierre Kervella, Simon Borgniet, Alexandre Gallenne, N. Nardetto, L. Breuval, Joseph Louis LAGRANGE (LAGRANGE), Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Observatoire de la Côte d'Azur (OCA), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), European Southern Observatory (ESO), Eurecom [Sophia Antipolis], Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratoire Hippolyte Fizeau (FIZEAU), Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Shock wave, Physics, stars: chromospheres, 010308 nuclear & particles physics, Infrared, Cepheid variable, chemistry.chemical_element, Astronomy and Astrophysics, Astrophysics, shock waves, Calcium, 01 natural sciences, chemistry, 13. Climate action, Space and Planetary Science, 0103 physical sciences, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], 010303 astronomy & astrophysics, Chromosphere, techniques: spectroscopic, stars: variables: Cepheids
Abstract

Context. It has recently been shown that the infrared (IR) emission of Cepheids, constant over the pulsation cycle, might be due to a pulsating shell of ionized gas with a radius of about 15% of that of the star radius, which could be attributed to the chromospheric activity of Cepheids. Aims. The aim of this paper is to investigate the dynamical structure of the chromosphere of Cepheids along the pulsation cycle and to quantify its size. Methods. We present Hα and calcium near-infrared triplet (Ca IR) profile variations using high-resolution spectroscopy with the UVES spectrograph of a sample of 24 Cepheids with a good period coverage from ≈3 to 60 days. After a qualitative analysis of the spectral line profiles, we quantified the Van Hoof effect (velocity gradient between the Hα and Ca IR) as a function of the period of the Cepheids. We then used the Schwarzschild mechanism (a line doubling due to a shock wave) to quantify the size of the chromosphere. Results. We find a significant Van Hoof effect for Cepheids with a period larger than P = 10 days. In particular, Hα lines are delayed with a velocity gradient up to Δv ≈ 30 km s−1 compared to Ca IR. By studying the shocks, we find that the size of the chromosphere of long-period Cepheids is of at least ≈50% of the stellar radius, which is consistent at first order with the size of the shell made of ionized gas previously found from the analysis of IR excess. Last, for most of the long-period Cepheids in the sample, we report a motionless absorption feature in the Hα line that we attribute to a circumstellar envelope that surrounds the chromosphere. Conclusions. Analyzing the Ca IR lines of Cepheids is of importance to potentially unbias the period–luminosity relation from their IR excess, particularly in the context of forthcoming observations of radial velocity measurements from the Radial Velocity Spectrometer on board Gaia, which could be sensitive to their chromosphere.

Published
2020
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4. Asymmetric shocks in $\chi$ Cyg observed with linear spectropolarimetry

Author

Julien Morin, E. S. Carlin, B. Tessore, Ph. Mathias, A. López Ariste, Michel Aurière, Fabrice Herpin, D. Gillet, Agnès Lèbre, Pascal Petit, Institut de recherche en astrophysique et planétologie (IRAP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG ), Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Instituto de Astrofisica de Canarias (IAC), Universidad de La Laguna [Tenerife - SP] (ULL), Istituto Ricerche Solari Locarno, Laboratoire Univers et Particules de Montpellier (LUPM), Université Montpellier 2 - Sciences et Techniques (UM2)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Observatoire de Haute-Provence (OHP), Institut Pythéas (OSU PYTHEAS), Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Institut de Recherche pour le Développement (IRD), Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), supported by 'Programme National de Physique Stellaire' (PNPS) of CNRS/INSU co-funded by CEA and CNES, Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), Centre National d'Études Spatiales [Toulouse] (CNES)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Centre National de la Recherche Scientifique (CNRS), Université de Montpellier (UM)-Université Montpellier 2 - Sciences et Techniques (UM2)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Franche-Comté Électronique Mécanique, Thermique et Optique - Sciences et Technologies (UMR 6174) (FEMTO-ST), Université de Franche-Comté (UFC)-Centre National de la Recherche Scientifique (CNRS)-Ecole Nationale Supérieure de Mécanique et des Microtechniques (ENSMM)-Université de Technologie de Belfort-Montbeliard (UTBM), FEMIS 2021, Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Centre National de la Recherche Scientifique (CNRS), and Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo-France -Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo-France -Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Convection, stars, Stars: imaging, 010504 meteorology & atmospheric sciences, Astrophysics::High Energy Astrophysical Phenomena, variables, Astrophysics, 01 natural sciences, Spectral line, Astronomical spectroscopy, Spherical geometry, Stars: HD 187796, 0103 physical sciences, Radiative transfer, Astrophysics::Solar and Stellar Astrophysics, general -stars, 010303 astronomy & astrophysics, ComputingMilieux_MISCELLANEOUS, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, Physics, Photosphere, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], [SDU.ASTR.SR]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], Computer Science::Information Retrieval, Astronomy and Astrophysics, Techniques: polarimetry, Astrophysics - Solar and Stellar Astrophysics, imaging -techniques, Space and Planetary Science, Homogeneous, Astrophysics::Earth and Planetary Astrophysics, polarimetric, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Stars: variable
Abstract

Aims: From a coherent interpretation of the linear polarisation detected in the spectral lines of the Mira star $\chi$ Cyg, we derive information about the dynamics of the stellar photosphere, including pulsation. Methods: From spectropolarimetric observations of $\chi$ Cyg, we perform careful analysis of the polarisation signals observed in atomic and molecular lines, both in absorption and emission, using the radiative transfer in the polarisation context, through two mechanisms: intrinsic polarisation and continuum depolarisation. We also explain the observed line doubling phenomenon in terms of an expanding shell in spherical geometry, which allows us to pinpoint the coordinates over the stellar disk with enhanced polarisation. Results: We find that the polarised spectrum of $\chi$ Cyg is dominated by intrinsic polarisation, with a negligible continuum depolarisation. The observed polarised signals can only be explained by assuming that this polarisation is locally enhanced by velocity fields. During the pulsation, radial velocities are not homogeneous over the disk. We map these regions of enhanced velocities. Conclusions: We have set an algorithm to distinguish in any stellar spectra of linear polarisation the origin of this polarisation and the way to increase signal by coherently adding many lines with an appropriated weight. Applied to the Mira star $\chi$ Cyg, we reached the unexpected result that during the pulsation, velocities are radial but not homogeneous over the disk. The reason for these local velocity enhancements are probably related to the interplay between the atmospheric pulsation dynamics and the underlying stellar convection., Comment: Accepted for publication in A&A

Published
2019
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5. New Nonlinear Model for the Long-Periodic Puzzling Cepheid l Car: Theoryvs.Observations

Author

A. Fokin, Ph. Mathias, and N. Nardetto

Subjects
Physics, Nonlinear system, Space and Planetary Science, Cepheid variable, Astrophysics::High Energy Astrophysical Phenomena, Nonlinear model, General Engineering, Radiative transfer, Astrophysics::Solar and Stellar Astrophysics, Astronomy and Astrophysics, Astrophysics, Circumstellar envelope, Astrophysics::Galaxy Astrophysics
Abstract

A nonlinear radiative pulsating model for the long-periodic Cepheid l Carinae is presented. The LTE metallic lines and non-LTE hydroen lines are calculated and compared with the HARPS observations. We found that the weak and medium metallic lines well correspond to the radial Cepheid pulsation, while the H α and some other strong lines reveal very strange behaviour which is not consistent with usual Cepheid pulsation. We conclude that l Car must have an extended circumstellar envelope, and discuss its possible parameters.

Published
2009
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6. Probing the dynamical structure ofδ Cephei atmosphere

Author

Denis Mourard, Ph. Mathias, N. Nardetto, and A. Fokin

Subjects
Physics, 010308 nuclear & particles physics, Cepheid variable, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, Spectral line, Interferometry, Wavelength, 13. Climate action, Space and Planetary Science, Limb darkening, Angular diameter, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Basso continuo, Spectroscopy, 010303 astronomy & astrophysics
Abstract

Context. Limb darkening and the projection factor are currently two limiting aspects of the interferometric Baade-Wesselink method of Cepheid distance determination. Aims. We first quantify the impact of the phase dependence of limb darkening on the derived distance. We then study a new way to probe the dynamical structure of Cepheid’s atmosphere through spectro-interferometric observations. Methods. A hydrodynamical model of δ Cep is used to derive stellar disk intensity distribution in the continuum and in different spectral lines, together with the corresponding wavelength- and phase-dependent visibility curves. Results. We find that considering a constant limb darkening in the visible leads to a systematic shift of about 0.02 in phase on the angular diameter curve. The derived distance is, however, not affected by this effect. Otherwise, for a spectroscopic resolution of R = 12 000 in the visible, we find in the most favourable case (maximum contraction velocity) a signature on the visibility curve of about 7% that is clearly detectable by current spectro-interferometers. Nevertheless, the projection factor has only a 1% (or less) effect on the visibility curve. Conclusions. The spectro-interferometry provides a new geometric view of Cepheid’s atmosphere. However, the combination of different techniques (high resolution spectroscopy, spectro- and differential-interferometry) are now needed to efficiently constrain the physical parameters of Cepheids’ atmosphere and, in particular the projection factor.

Published
2006
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7. Self consistent modelling of the projection factor for interferometric distance determination

Author

Nicolas Nardetto, Denis Mourard, D. Bersier, Ph. Mathias, Pierre Kervella, A. B. Fokin, Laboratoire Gemini (LG), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Pôle Astronomie du LESIA, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris

Subjects
Physics, Limiting factor, 010504 meteorology & atmospheric sciences, business.industry, Cepheid variable, Observational techniques, Astronomy and Astrophysics, Astrophysics, Radius, 01 natural sciences, Computational physics, Radial velocity, Optics, Space and Planetary Science, Angular diameter, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], business, Projection (set theory), 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Line (formation)
Abstract

The distance of galactic Cepheids can be derived through the interferometric Baade-Wesselink method. The interfer- ometric measurements lead to angular diameter estimations over the whole pulsation period, while the stellar radius variations can be deduced from the integration of the pulsation velocity. The latter is linked to the observational velocity deduced from line profiles by the so-called projection factor p. The knowledge of p is currently an important limiting factor for this method of distance determination. A self-consistent and time-dependent model of the star δ Cep is computed in order to study the dynamical structure of its atmosphere together with the induced line profile. Different kinds of radial and pulsation velocities are then derived. In particular, we compile a suitable average value for the projection factor related to different observational techniques, such as spectrometry, and spectral-line or wide-band interferometry. We show that the impact on the average pro- jection factor and consequently on the final distance deduced from this method is of the order of 6%. We also study the impact of a constant or variable p-factor on the Cepheid distance determination. We conclude on this last point that if the average value of the projection factor is correct, then the influence of the time dependence is not significant as the error in the final distance is of the order of 0.2%.

Published
2004
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8. HD 173977: An ellipsoidal δ Scuti star variable

Author

Ignasi Ribas, M. Alvarez, Ph. Mathias, R. Garrido, J. M. Le Contel, Andrés Moya, J. P. Sareyan, E. Chapellier, L. Parrao, J. H. Pena, Laboratoire Gemini (LG), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, and Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Physics, G-type main-sequence star, 010308 nuclear & particles physics, Hertzsprung–Russell diagram, Astronomy, Astronomy and Astrophysics, Astrophysics, Star (graph theory), A-type main-sequence star, Light curve, 01 natural sciences, symbols.namesake, [SDU]Sciences of the Universe [physics], Space and Planetary Science, 0103 physical sciences, Binary star, symbols, Binary system, 010303 astronomy & astrophysics, O-type main-sequence star
Abstract

We present spectroscopic and photometric observations of the star HD 173977. It appears that the star is part of a double line binary system, with a period of 1.801 d, corresponding to twice the period of the photometric variations. Hence the star is an ellipsoidal variable. The system is probably synchronized. The physical parameters of both components were derived through two independant methods, one based on evolutionary tracks, the other being the result of the behaviour of light curves in a close binary system. After removing the ellipsoidal variations, 3 frequencies are detected in the photometric data: 8.56, 14.51 and 16.42 d -1 , while 2 additional frequencies are also possible: 10.96 and 12.11 d -1 . In accordance with its position in the HR diagram, the primary component of HD 173977 should be considered as a δ Scuti star and no longer as a γ Doradus star. In addition, HD 173844, used as a check star, is discovered variable with a 15.79 d -1 frequency and is classified as a δ Scuti star.

Published
2004
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9. Pulsation of the $\delta$ Scuti multiple system DG Leo

Author

J. H. Pena, J. Cuypers, L. Parrao, P. van Cauteren, Ph. Mathias, Torben Arentoft, Herman Hensberge, M. Hobart, Patricia Lampens, Yves Fremat, R. Garrido, and P. De Cat

Subjects
Physics, Delta, Space and Planetary Science, Component (thermodynamics), Triple system, Astrophysics::Solar and Stellar Astrophysics, Astronomy, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Astrophysics::Galaxy Astrophysics
Abstract

DG Leo is a spectroscopic triple system showing Scuti type photometric and spectroscopic variations. The three components have nearly equal masses but different chemical compositions in the outer layers. All three are potential pulsators. Frequency analyses of the photometric data were carried out using various methods. These global results together with those of the spectroscopic analysis permit us to discuss of the behaviour of each component with respect to pulsation.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Published
2004
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10. High resolution spectroscopy of the triple system 20 Leo

Author

Torben Arentoft, J. H. Pena, P. van Cauteren, P. De Cat, Ph. Mathias, L. Parrao, Herman Hensberge, Patricia Lampens, Yves Fremat, and R. Garrido

Subjects
Physics, Orbital elements, business.industry, Effective temperature, Surface gravity, Spectral line, Fourier transform spectroscopy, Computational physics, symbols.namesake, Stars, Fourier transform, Optics, symbols, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, business, Spectrograph
Abstract

20 Leo is a spectroscopic triple system composed of 3 very similar stars, one of which seems to be aδSct star. Observations at high spectral and high time resolution have been obtained at the Observatoire de Haute Provence with the ELODIE spectrograph on the 1.9-m telescope. The spectra were taken during 7 nights in 2003 January and cover the whole optical domain from 3900 to 6800 Å. We used a Fourier transform technique recently developed by P. Hadrava to disentangle the combined spectrum. Application of the method allows the derivation of radial velocities at all orbital phases (even at phases of complete blending), as well as individual spectra for each component. From these computations we deduced more accurate individual radial velocities and improved orbital parameters describing the motion of the inner binary. Model atmospheres were used to analyze each individual spectrum and determine stellar fundamental parameters of the three components such as effective temperature, surface gravity and projected rotation velocity.

Published
2004
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11. MATISSE: perspective of imaging in the mid-infrared at the VLTI

Author

B. Lopez, P. Antonelli, S. Wolf, S. Lagarde, W. Jaffe, R. Navarro, U. Graser, R. Petrov, G. Weigelt, Y. Bresson, K. H. Hofmann, U. Beckman, T. Henning, W. Laun, Ch. Leinert, S. Kraus, S. Robbe-Dubois, F. Vakili, A. Richichi, P. Abraham, J.-C. Augereau, J. Behrend, Ph. Berio, N. Berruyer, O. Chesneau, J. M. Clausse, C. Connot, K. Demyk, W. C. Danchi, M. Dugué, G. Finger, S. Flament, A. Glazenborg, H. Hannenburg, M. Heininger, Y. Hugues, J. Hron, S. Jankov, F. Kerschbaum, G. Kroes, H. Linz, J.-L. Lizon, Ph. Mathias, R. Mathar, A. Matter, J. L. Menut, K. Meisenheimer, F. Millour, N. Nardetto, U. Neumann, E. Nussbaum, A. Niedzielski, L. Mosoni, J. Olofsson, Y. Rabbia, T. Ratzka, F. Rigal, A. Roussel, D. Schertl, F.-X. Schmider, B. Stecklum, E. Thiebaut, M. Vannier, B. Valat, K. Wagner, and L. B. F. M. Waters

Subjects
Physics, Very Large Telescope, business.industry, Aperture synthesis, Astrophysics::Instrumentation and Methods for Astrophysics, Spectral bands, law.invention, Telescope, Optics, law, Observatory, Closure phase, Astronomical interferometer, Astrophysics::Solar and Stellar Astrophysics, Angular resolution, Astrophysics::Earth and Planetary Astrophysics, business, Astrophysics::Galaxy Astrophysics, Remote sensing
Abstract

MATISSE is foreseen as a mid-infrared spectro-interferometer combining the beams of up to four UTs/ATs of the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory. The related science case study demonstrates the enormous capability of a new generation mid-infrared beam combiner. MATISSE will constitute an evolution of the two-beam interferometric instrument MIDI. MIDI is a very successful instrument which offers a perfect combination of spectral and angular resolution. New characteristics present in MATISSE will give access to the mapping and the distribution of the material (typically dust) in the circumstellar environments by using a wide mid-infrared band coverage extended to L, M and N spectral bands. The four beam combination of MATISSE provides an efficient UV-coverage : 6 visibility points are measured in one set and 4 closure phase relations which can provide aperture synthesis images in the mid-infrared spectral regime.

Published
2008
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12. MATISSE, perspective of imaging in the mid-infrared at the VLTI

Author

Lopez, B., Antonelli, P., Wolf, S., Lagarde, S., Jaffe, W., Navarro, R., Graser, U., Petrov, R., Weigelt, G., Bresson, Y., Hofmann, K. H., Beckman, U., Henning, T., Laun, W., Ch. Leinert, Robbe-Dubois, S., Vakili, F., Richichi, A., Abraham, P., C Augereau, J., Behrend, J., Ph. Berio, Berruyer, N., Chesneau, O., Clausse, J. M., Connot, C., Demyk, K., Danchi, W. C., Dugué, M., Finger, G., Flament, S., Glazenborg, A., Hannenburg, H., Heininger, M., Hugues, Y., Hron, J., Jankov, S., Kerschbaum, F., Kroes, G., Linz, H., L Lizon, J., Ph. Mathias, Mathar, R., Matter, A., Menut, J. L., Meisenheimer, K., Millour, F., Nardetto, N., Neumann, U., Nussbaum, E., Niedzielski, A., Mosoni, L., Olofsson, J., Rabbia, Y., Ratzka, T., Rigal, F., Roussel, A., Schertl, D., François-Xavier Schmider, Stecklum, B., Éric Thiébaut, Vannier, M., Valat, B., Wagner, K., Waters, L. B. F. M., Laboratoire Hippolyte Fizeau (FIZEAU), Université Nice Sophia Antipolis (... - 2019) (UNS), Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Max-Planck-Institut für Astronomie (MPIA), Max-Planck-Gesellschaft, Laboratoire Universitaire d'Astrophysique de Nice (LUAN), Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Max-Planck-Institut für Radioastronomie (MPIFR), Observatoire de la Côte d'Azur (OCA), Centre National de la Recherche Scientifique (CNRS), European Southern Observatory (ESO), Laboratoire d'Astrophysique de Grenoble (LAOG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Institut für Astrophysik [Wien], Universität Wien, Thüringer Landessternwarte Tautenburg (TLS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), and Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Astrophysics::Instrumentation and Methods for Astrophysics, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Astrophysics::Galaxy Astrophysics
Abstract

International audience; MATISSE is foreseen as a mid-infrared spectro-interferometer combining the beams of up to four UTs/ATs of the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory. The related science case study demonstrates the enormous capability of a new generation mid-infrared beam combiner. MATISSE will constitute an evolution of the two-beam interferometric instrument MIDI. MIDI is a very successful instrument which offers a perfect combination of spectral and angular resolution. New characteristics present in MATISSE will give access to the mapping and the distribution of the material (typically dust) in the circumstellar environments by using a wide mid-infrared band coverage extended to L, M and N spectral bands. The four beam combination of MATISSE provides an efficient UV-coverage : 6 visibility points are measured in one set and 4 closure phase relations which can provide aperture synthesis images in the mid-infrared spectral regime.

Published
2008

13. High resolution spectroscopy for Cepheids distance determination. II. A period- projection factor relation

Author

N. Nardetto, D. Mourard, Ph. Mathias, A. Fokin, D. Gillet, Laboratoire Gemini (LG), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, and Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Physics, 010308 nuclear & particles physics, Cepheid variable, media_common.quotation_subject, Milky Way, Astrophysics (astro-ph), FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, Asymmetry, Spectral line, Galaxy, Radial velocity, Stars, 13. Climate action, Space and Planetary Science, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, 010303 astronomy & astrophysics, media_common, Line (formation)
Abstract

Galactic Cepheids in the vicinity of the Sun have a residual line-of-sight velocity, or gamma-velocity, which shows a systematic blueshift of about 2 km/s compared to an axisymmetric rotation model of the Milky Way. This term is either related to the space motion of the star and, consequently, to the kinematic structure of our Galaxy, or it is the result of the dynamical structure of the Cepheids' atmosphere. We aim to show that these residual gamma-velocities are an intrinsic property of Cepheids. We observed nine galactic Cepheids with the HARPS spectroscope, focusing specifically on 17 spectral lines. For each spectral line of each star, we computed the gamma-velocity (resp. gamma-asymmetry) as an average value of the interpolated radial velocity (resp. line asymmetry) curve. For each Cepheid in our sample, a linear relation is found between the gamma-velocities of the various spectral lines and their corresponding gamma-asymmetries, showing that residual gamma-velocities stem from the intrinsic properties of Cepheids. We also provide a physical reference to the stellar gamma-velocity: it should be zero when the gamma-asymmetry is zero. Following this definition, we provide very precise and physically calibrated estimates of the gamma-velocities for all stars of our sample. To understand this very subtle gamma-asymmetry effect, further numerical studies are needed. Cepheids' atmosphere are strongly affected by pulsational dynamics, convective flows, nonlinear physics, and complex radiative transport. Hence, all of these effects have to be incorporated simultaneously and consistently into the numerical models to reproduce the observed line profiles in detail.

Published
2008
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14. High resolution spectroscopy for Cepheids distance determination. I. Line asymmetry

Author

D. Bersier, Ph. Mathias, Nicolas Nardetto, Denis Mourard, Antoine Mérand, Pierre Kervella, Laboratoire Gemini (LG), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, and Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Physics, 010308 nuclear & particles physics, Cepheid variable, media_common.quotation_subject, Astrophysics (astro-ph), FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Rotation, 01 natural sciences, Asymmetry, Spectral line, Radial velocity, Stars, Space and Planetary Science, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, Spectral resolution, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Line (formation), media_common
Abstract

The ratio of pulsation to radial velocity (the projection factor) is currently limiting the accuracy of the interferometric Baade-Wesselink method. This work aims at establishing a link between the line asymmetry evolution over the Cepheids' pulsation cycles and their projection factor, with the final objective to improve the accuracy of the Baade-Wesselink method for distance determinations. We present HARPS high spectral resolution observations of nine galactic Cepheids having a good period sampling. We fit spectral line profiles by an asymmetric bi-Gaussian to derive radial velocity, Full-Width at Half-Maximum in the line (FWHM) and line asymmetry for all stars. We then extract correlations curves between radial velocity and asymmetry. A geometric model providing synthetic spectral lines, including limb-darkening, a constant FWHM (hereafter sigma_c) and the rotation velocity is used to interpret these correlations curves. For all stars, comparison between observations and modelling is satisfactory, and we were able to determine the projected rotation velocities and sigma_c for all stars. We also find a correlation between the rotation velocity (Vrot sin i) and the period of the star: Vrot sin i = (11.5 +- 0.9) log(P) + (19.8 +- 1.0) [km/s]. Moreover, we observe a systematic shift in observational asymmetry curves (noted gamma_O), related to the period of the star, which is not explained by our static model: gamma_O = (10.7+-0.1) log(P) + (9.7+-0.2) [in %] . For long-period Cepheids, in which velocity gradients, compression or shock waves seem to be large compared to short- or medium period Cepheids we observe indeed a greater systematic shift in asymmetry curves. (abridged)

Published
2008
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15. APerture Synthesis in the MID-Infrared with the VLTI

Author

Uwe Graser, Ph. Gitton, E. DiFolco, Andreas Glindemann, Slobodan Jankov, Karl-Heinz Hofmann, E. Thiéebaut, Dieter Schertl, François-Xavier Schmider, Gerd Weigelt, H. Linz, Ph. Mathias, S. Flament, W. Jaffe, Ch. Leinert, B. Stecklum, Andrzej Niedzielski, F. Vakili, Anne Dutrey, A. Roussel, Ralf-Rainer Rohloff, S. Lagarde, J. Behrend, Sebastian Wolf, C. Connot, M. Duguée, Nicole Berruyer, P. Antonelli, J. C. Augereau, Udo Neumann, L. Mosoni, A. Glazenborg, Klaus Meisenheimer, J.-L. Menut, M. Heininger, K. Demyk, Bruno Lopez, Karl Wagner, Thorsten Ratzka, O. Chesneau, Y. Hugues, Th. Henning, Stefan Kraus, Y. Bresson, Frank Przygodda, and Florence Puech

Subjects
Physics, MIDI, business.industry, Aperture synthesis, Astrophysics::Instrumentation and Methods for Astrophysics, Mid infrared, computer.file_format, Interferometry, Optics, Closure phase, Astrophysics::Solar and Stellar Astrophysics, Spectral energy distribution, Visibility, business, computer, Beam (structure), Remote sensing
Abstract

Our objective is to develop of the mid-infrared imaging for the VLTI. Several areas of astrophysics will benefit of this new capability. APreS-MIDI comprises a beam combiner which interfaces with the current MIDI instrument. It thus constitutes an extension to the two-beam interferometric instrument MIDI by increasing the number of recombined beams up to four. This extension provides better uv-coverage (6 visibility points measured in one set) and moreover will allow measurement of 4 closure phase relations thus providing for the first time aperture synthesis images in the mid-infrared spectral regime.

Published
2007
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17. First AMBER/VLTI Observations of Hot Massive Stars

Author

Romain Petrov, Millour, F., Chesneau, O., Weigelt, G., Bonneau, D., Ph. Stee, Kraus, S., Mourard, D., Meilland, A., Vannier, M., Malbet, F., Lisi, F., Antonelli, P., Kern, P., Beckmann, U., Lagarde, S., Perraut, K., Gennari, S., Le Coarer, E., Th. Driebe, Accardo, M., Robbe-Dubois, S., Ohnaka, K., Busoni, S., Roussel, A., Zins, G., Behrend, J., Ferruzi, D., Bresson, Y., Duvert, G., Nussbaum, E., Marconi, A., Ph. Feautrier, Dugué, M., Chelli, A., Tatulli, E., Heininger, M., Delboulbe, A., Bonhomme, S., Schertl, D., Testi, L., Ph. Mathias, L Monin, J., Gluck, L., Hofmann, K. H., Salinari, P., Puget, P., Clausse, J. M., Didier Fraix-Burnet, D., Renaud Foy, Isella, A., Laboratoire Universitaire d'Astrophysique de Nice (LUAN), Université Nice Sophia Antipolis (... - 2019) (UNS), Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'Astrophysique de Grenoble (LAOG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Max-Planck-Institut für Astronomie (MPIA), Max-Planck-Gesellschaft, Laboratoire Gemini (LG), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Max-Planck-Institut für Radioastronomie (MPIFR), European Southern Observatory (ESO), INAF - Osservatorio Astrofisico di Arcetri (OAA), Istituto Nazionale di Astrofisica (INAF), Centre de Recherche Astrophysique de Lyon (CRAL), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-École normale supérieure - Lyon (ENS Lyon), Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS), École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), and Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)

Subjects
[PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), Astrophysics::Instrumentation and Methods for Astrophysics, FOS: Physical sciences, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Astrophysics, Astrophysics::Galaxy Astrophysics
Abstract

8 pages; International audience; AMBER is the first near infrared focal instrument of the VLTI. It combines three telescopes and produces spectrally resolved interferometric measures. This paper discusses some preliminary results of the first scientific observations of AMBER with three Unit Telescopes at medium (1500) and high (12000) spectral resolution. We derive a first set of constraints on the structure of the circumstellar material around the Wolf Rayet gamma2 Velorum and the LBV eta Carinae.

Published
2005

18. Hydrodynamic models for b Cephei variables. I. BW Vulpeculae revisited

Author

Ph. Mathias, E. Chapellier, N. Nardetto, D. Gillet, A. Fokin, Laboratoire Gemini (LG), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, and Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Shock wave, Physics, 010308 nuclear & particles physics, Metallicity, Astronomy, Astronomy and Astrophysics, Astrophysics, Gas dynamics, 01 natural sciences, Spectral line, Amplitude, Space and Planetary Science, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, 010303 astronomy & astrophysics, Line (formation)
Abstract

A hydrodynamical model is generated for the high-amplitude β Cephei star BW Vulpeculae, and the spectral line profiles are calculated for different pulsational phases. The pulsational characteristics and line profiles are compared with recent observational data obtained during seven consecutive nights in August 2000. We found a generally good agreement in the basic photometric and spectral parameters. Two strong shock waves appear during one period, and the "stillstand" is due to the gas dynamics between the passages of these shocks. Note that this good agreement suppose a metallicity Z = 0.03, while a metallicity Z = 0.02 does not lead to the correct amplitudes and shapes of the curves.

Published
2004
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19. Atmospheric Abundances in Post-AGB candidates of Intermediate Temperature

Author

Ph. Mathias, A. Arellano Ferro, and Sunetra Giridhar

Subjects
Physics, Stars, Nebula, Space and Planetary Science, Red giant, Astrophysics (astro-ph), Intermediate temperature, FOS: Physical sciences, Astronomy and Astrophysics, Emission spectrum, Astrophysics, Supergiant
Abstract

Detailed atmospheric abundances have been calculated for a sample of A-G supergiant stars with IR fluxes and/or high galactic latitudes. HD 172481 and HD 158616 show clear indications of being post-AGB stars that have experienced third dredge-up. HD 158616 is carbon-rich while the abundance pattern of HD 172481 and its large Li enhancement gives support to the hot bottom burning scenario that explains paucity of carbon-rich stars among AGB stars. HD 172324 is very likely a hot post-AGB star that shows a strong carbon deficiency. HD 725, HD 218753 and HD 331319 also appear to be evolved objects between the red giant and the AGB. HD 9167, HD 173638 with a few exceptions, reflect solar abundances and no signs of post red giant evolution. They are most likely young massive disk supergiants. Further analysis of proto-Planetary Nebula HDE 341617 reveals that He lines show signs of velocity stratification. The emission lines have weakened considerably since 1993. The envelope expands at 19 km s$^{-1}$ relative to the star. Atmospheric abundances, evolutionary tracks and isochrones are used to estimate masses and ages of all stars in the sample., Comment: 19 pages (text), 14 tables, 5 figures

Published
2001
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20. First AMBER/VLTI Observations of Hot Massive Stars

Author

R. G. Petrov, F. Millour, O. Chesneau, G. Weigelt, D. Bonneau, Ph. Stee, S. Kraus, D. Mourard, A. Meilland, M. Vannier, F. Malbet, F. Lisi, P. Antonelli, P. Kern, U. Beckmann, S. Lagarde, K. Perraut, S. Gennari, E. Le Coarer, Th. Driebe, M. Accardo, S. Robbe-Dubois, K. Ohnaka, S. Busoni, A. Roussel, G. Zins, J. Behrend, D. Ferruzi, Y. Bresson, G. Duvert, E. Nussbaum, A. Marconi, Ph. Feautrier, M. Dugué, A. Chelli, E. Tatulli, M. Heininger, A. Delboulbe, S. Bonhomme, D. Schertl, L. Testi, Ph. Mathias, J. -L. Monin, L. Gluck, K. H. Hofmann, P. Salinari, P. Puget, J. M. Clausse, D. Fraix-Burnet, R. Foy, and A. Isella

Subjects
Physics, Astrophysics::High Energy Astrophysical Phenomena, Near-infrared spectroscopy, Astrophysics::Instrumentation and Methods for Astrophysics, Astrophysics, 01 natural sciences, 010309 optics, Interferometry, Stars, Wolf–Rayet star, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Spectral resolution, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics
Abstract

AMBER is the first near infrared focal instrument of the VLTI. It combines three telescopes and produces spectrally resolved interferometric measures. This paper discusses some preliminary results of the first scientific observations of AMBER with three Unit Telescopes at medium (1500) and high (12000) spectral resolution. We derive a first set of constraints on the structure of the circumstellar material around the Wolf Rayet Gamma2 Velorum and the LBV Eta Carinae.

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