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Start Over Author "Wittkowski, Markus" Topic astrophysics::galaxy astrophysics
12 results on '"Wittkowski, Markus"'

1. Investigating mass loss from evolved stars: First results and perspectives using VLTI-MATISSE

Author

Wittkowski, Markus

Subjects
Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Astrophysics::Galaxy Astrophysics
Abstract

Cool evolves stars, including asymptotic giant branch (AGB) red supergiants (RSGs) form molecules and dust in their atmospheres, which are subsequently expelled into the interstellar medium via stellar winds. For AGB stars, it has been shown that pulsation and convection lead to strongly extended molecular atmospheres, where the temperature is cool enough for dust to form. For RSGs, however, current dynamic model atmospheres of RSGs, based on pulsation and convection alone, cannot explain observed extensions of RSG atmospheres by far. Here, we present first preliminary results of our mid-infrared interferometric imaging of one AGB star, R Aqr, and one RSG, AH Sco, obtained with the newly available VLTI-MATISSE instrument during science verification and early science operations. We also present our plans to further follow up on evolved star imaging at near- and mid-infrared to constrain latest dynamic models of the mass loss process.

Published
2020
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2. Precision Monitoring of Cool Evolved Stars: Constraining Effects of Convection and Pulsation

Author

Wittkowski, Markus, Bladh, Sara, Chiavassa, Andrea, De Wit, Willem-Jan, Eriksson, Kjell, Freytag, Bernd, Haubois, Xavier, Höfner, Susanne, Kravchenko, Kateryna, Paladini, Claudia, Paumard, Thibaut, Rau, Gioia, and Wood, Peter R.

Subjects
Astrophysics::Instrumentation and Methods for Astrophysics, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Astrophysics::Galaxy Astrophysics
Abstract

Mass loss from cool evolved stars is an important ingredient of the cosmic matter cycle, enriching the Universe with newly formed elements and dust. However, physical processes that are not considered in current models represent uncertainties in our general understanding of mass loss. Time-series of interferometric data provide the strongest tests of dynamical processes in the atmospheres of these stars. Here, we present a pilot study of such measurements obtained with the GRAVITY instrument on the Very Large Telescope Interferometer., Published in The Messenger vol. 178, pp. 34-35, December 2019.

Published
2019
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3. VLTI-PIONIER imaging of the carbon AGB star R Sculptoris and the supergiant V766 Centauri

Author

Wittkowski, Markus

Subjects
Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Astrophysics::Galaxy Astrophysics
Abstract

I will present reconstructed images of the carbon-rich AGB star R Scl and of the supergiant V766 Cen, both recently obtained from VLTI-PIONIER data. The images are compared to state-of-the art atmosphere and wind models. The images of R Scl exhibit a complex structure within the stellar disk. This structure is most likely caused by giant convection cells, resulting in large-scale shock fronts, and their effects on clumpy molecule and dust formation seen against the photosphere. Images of V 766 Cen were obtained at three epochs. The first epoch shows a complex elongated structure within the photospheric disk, consistent with a red supergiant harboring giant photospheric convection cells. The second and third epochs show a qualitatively and quantitatively different structure with significantly increased contrast, which is not compatible with current models of convection. Instead we interpret the 2016 and 2017 epochs as showing a previously suggested close eclipsing companion in front of the primary, which was located behind the primary at the 2014 epoch. Finally, I will show preliminary reconstructed images of a small sample of further red supergiants.

Published
2018
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4. Constraining Convection in Evolved Stars with the VLTI

Author

Paladini, Claudia, Baron, Fabien, Jorissen, Alain, Le Bouquin, Jean-Baptiste, Freytag, Bernd, Van Eck, Sophie, Wittkowski, Markus, Hron, Josef, Chiavassa, Andrea, Berger, Jean-Philippe, Siopis, Christos, Mayer, Andreas, Sadowski, Gilles, Kravchenko, Kateryna, Shetye, Shreeya, Kerschbaum, Franz, Kluska, Jacques, and Ramstedt, Sofia

Subjects
Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Astrophysics::Galaxy Astrophysics
Abstract

We used the Precision Integrated-Optics Near-infrared Imaging ExpeRiment (PIONIER) at the Very Large Telescope Interferometer (VLTI) to image the stellar surface of the S-type Asymptotic Giant Branch (AGB) star π1 Gruis. The angular resolution of two milliarcseconds allowed us to observe the surface of this giant star in unprecedented detail. At the observed wavelength the stellar disc appears circular and dust-free. Moreover, the disc is characterised by a few bubbles of a convective nature. We determine the contrast, and the characteristic horizontal length-scale of the convective granules. The latter is determined, for the first time, directly from the image, without involving the usual geometric modelling that has been used in the literature. The measurements fall along empirical scaling relations between stellar parameters and convective sizes, which are determined on the basis of three-dimensional stellar convection models. Our results open up a new era for the characterisation of stellar convection in stars other than the Sun., Published in The Messenger vol. 172, pp. 24-26, June 2018.

Published
2018
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5. Multiple star systems in the Orion nebula

Author

GRAVITY Collaboration, Karl, Martina, Pfuhl, Oliver, Eisenhauer, Frank, Genzel, Reinhard, Grellmann, Rebekka, Habibi, Maryam, Abuter, Roberto, Accardo, Matteo, Amorim, Ant��nio, Anugu, Narsireddy, ��vila, Gerardo, Benisty, Myriam, Berger, Jean-Philippe, Bland, Nicolas, Bonnet, Henri, Bourget, Pierre, Brandner, Wolfgang, Brast, Roland, Buron, Alexander, Garatti, Alessio Caratti o, Chapron, Fr��d��ric, Cl��net, Yann, Collin, Claude, Foresto, Vincent Coud�� du, de Wit, Willem-Jan, de Zeeuw, Tim, Deen, Casey, Delplancke-Str��bele, Fran��oise, Dembet, Roderick, Derie, Fr��d��ric, Dexter, Jason, Duvert, Gilles, Ebert, Monica, Eckart, Andreas, Esselborn, Michael, F��dou, Pierre, Finger, Gert, Garcia, Paulo, Dabo, Cesar Enrique Garcia, Lopez, Rebeca Garcia, Gao, Feng, Gandron, ��ric, Gillessen, Stefan, Gont��, Fr��d��ric, Gordo, Paulo, Gr��zinger, Ulrich, Guajardo, Patricia, Guieu, Sylvain, Haguenauer, Pierre, Hans, Oliver, Haubois, Xavier, Haug, Marcus, Hau��mann, Frank, Henning, Thomas, Hippler, Stefan, Horrobin, Matthew, Huber, Armin, Hubert, Zoltan, Hubin, Norbert, Hummel, Christian A., Jakob, Gerd, Jochum, Lieselotte, Jocou, Laurent, Kaufer, Andreas, Kellner, Stefan, Kandrew, Sarah, Kern, Lothar, Kervella, Pierre, Kiekebusch, Mario, Klein, Ralf, K��hler, Rainer, Kolb, Johan, Kulas, Martin, Lacour, Sylvestre, Lapeyr��re, Vincent, Lazareff, Bernard, Bouquin, Jean-Baptiste Le, L��na, Pierre, Lenzen, Rainer, L��v��que, Samuel, Lin, Chien-Cheng, Lippa, Magdalena, Magnard, Yves, Mehrgan, Leander, M��rand, Antoine, Moulin, Thibaut, M��ller, Eric, M��ller, Friedrich, Neumann, Udo, Oberti, Sylvain, Ott, Thomas, Pallanca, Laurent, Panduro, Johana, Pasquini, Luca, Paumard, Thibaut, Percheron, Isabelle, Perraut, Karine, Perrin, Guy, Pfl��ger, Andreas, Duc, Thanh Phan, Plewa, Philipp M., Popovic, Dan, Rabien, Sebastian, Ram��rez, Andr��s, Ramos, Jose, Rau, Christian, Riquelme, Miguel, Rodr��guez-Coira, Gustavo, Rohloff, Ralf-Rainer, Rosales, Alejandra, Rousset, G��rard, Sanchez-Bermudez, Joel, Scheithauer, Silvia, Sch��ller, Markus, Schuhler, Nicolas, Spyromilio, Jason, Straub, Odele, Straubmeier, Christian, Sturm, Eckhard, Suarez, Marcos, Tristram, Konrad R. W., Ventura, Noel, Vincent, Fr��d��ric, Waisberg, Idel, Wank, Imke, Widmann, Felix, Wieprecht, Ekkehard, Wiest, Michael, Wiezorrek, Erich, Wittkowski, Markus, Woillez, Julien, Wolff, Burkhard, Yazici, Senol, Ziegler, Denis, Zins, G��rard, Max Planck Institute for Extraterrestrial Physics (MPE), Max-Planck-Gesellschaft, European Southern Observatory (ESO), SIM/IDL Faculdade de Ciências da Universidade de Lisboa (FCUL), University of Lisboa, CENTRA Instituto Superior Tecnico, 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 de Planétologie et d'Astrophysique de Grenoble (IPAG), 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), European Southern Observatory [Santiago] (ESO), Max-Planck-Institut für Astronomie (MPIA), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Astronomie et techniques spatiales, Université Paris Diderot - Paris 7 (UPD7), Physikalisches Institut [Köln], Universität zu Köln, Centro de Astrofísica da Universidade do Porto (CAUP), Universidade do Porto [Porto], State Key Laboratory of Molecular Developmental Biology, Institute of genetics and developmental Biology, CAS, CENTRA, Universidade de Lisboa, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), leiden Obsevatory, Universiteit Leiden [Leiden], Laboratoire d'Astrophysique, Laboratoire des interactions plantes micro-organismes (LIPM), Centre National de la Recherche Scientifique (CNRS)-Institut National de la Recherche Agronomique (INRA), Matériaux divisés, interfaces, réactivité, électrochimie (MADIREL), Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS), Institut d'Astrophysique de Paris (IAP), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Observatoire de Paris - Site de Meudon (OBSPM), Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), Michigan State University [East Lansing], Michigan State University System, 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]), 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), Universität zu Köln = University of Cologne, Universidade do Porto = University of Porto, 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), Universiteit Leiden, Institut National de la Recherche Agronomique (INRA)-Centre National de la Recherche Scientifique (CNRS), Aix Marseille Université (AMU)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), European Project: 8003119(1980), Universidade do Porto, and Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)

Subjects
Initial mass function, Population, FOS: Physical sciences, Star count, Astrophysics, 01 natural sciences, 0103 physical sciences, Orion Nebula, Astrophysics::Solar and Stellar Astrophysics, education, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), ComputingMilieux_MISCELLANEOUS, O-type star, Physics, [PHYS]Physics [physics], education.field_of_study, 010308 nuclear & particles physics, Astronomy and Astrophysics, Mass ratio, Accretion (astrophysics), Stars, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Astrophysics::Earth and Planetary Astrophysics, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract

This work presents an interferometric study of the massive-binary fraction in the Orion Trapezium Cluster with the recently comissioned GRAVITY instrument. We observe a total of 16 stars of mainly OB spectral type. We find three previously unknown companions for $\theta ^1$ Ori B, $\theta ^2$ Ori B, and $\theta ^2$ Ori C. We determine a separation for the previously suspected companion of NU Ori. We confirm four companions for $\theta ^1$ Ori A, $\theta ^1$ Ori C, $\theta ^1$ Ori D, and $\theta ^2$ Ori A, all with substantially improved astrometry and photometric mass estimates. We refine the orbit of the eccentric high-mass binary $\theta ^1$ Ori C and we are able to derive a new orbit for $\theta ^1$ Ori D. We find a system mass of 21.7 $M_{\odot}$ and a period of $53$ days. Together with other previously detected companions seen in spectroscopy or direct imaging, eleven of the 16 high-mass stars are multiple systems. We obtain a total number of 22 companions with separations up to 600 AU. The companion fraction of the early B and O stars in our sample is about 2, significantly higher than in earlier studies of mostly OB associations. The separation distribution hints towards a bimodality. Such a bimodality has been previously found in A stars, but rarely in OB binaries, which up to this point have been assumed to be mostly compact with a tail of wider companions. We also do not find a substantial population of equal-mass binaries. The observed distribution of mass ratios declines steeply with mass, and like the direct star counts, indicates that our companions follow a standard power law initial mass function. Again, this is in contrast to earlier findings of flat mass ratio distributions in OB associations. We exclude collision as a dominant formation mechanism but find no clear preference for core accretion or competitive accretion., Comment: Accepted for publication in A&A

Published
2018
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6. Report on the ESO Workshop 'Imaging of Stellar Surfaces'

Author

Wittkowski, Markus and Humphreys, Liz

Subjects
Astrophysics::Instrumentation and Methods for Astrophysics, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Astrophysics::Galaxy Astrophysics
Abstract

There have recently been tremendous advances in observational techniques enabling the resolution of the surfaces of stars other than the Sun. Current VLTI instruments, SPHERE on the VLT, and ALMA, as well as other interferometric facilities, have recently succeeded in resolving stellar surfaces. The workshop aimed to bring together observers specialising in different techniques and wavelength regimes, and theoreticians working on stellar atmospheres and stellar structure. We aimed to organise a focused workshop with ample time devoted to the discussion of recent images of stellar surfaces and their extended atmospheres out to a few stellar radii, as well as observational strategies and the relevant underlying physical processes. The workshop was the first to be held in the seminar room of the new ESO Supernova Planetarium & Visitor Centre, and it was also the first workshop for which the new code of conduct for ESO workshops & conferences was in place, Published in The Messenger vol. 172, pp. 35-39, June 2018.

Published
2018
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7. First light for GRAVITY: Phase referencing optical interferometry for the Very Large Telescope Interferometer

Author

Abuter, Roberto, Accardo, Matteo, Antonio, Amorim, Narsireddy, Anugu, Avila, Gerardo, Azouaoui, N., Benisty, Myriam, Berger, Jean-Philippe, Blind, Nicolas, Bonnet, Henri, Bourget, Pierre, Brandner, Wolfgang, Brast, Roland, Buron, Alexander, Burtscher, L., Cassaing, Frederic, Chapron, Frédéric, Choquet, Elodie, Clénet, Yann, Collin, Claude, Coudé du Forestol, Vincent, de Wit, Willem-Jan, De Zeeuw, Tim, Casey, Deen, Delplancke-Ströbele, Françoise, Dembet, Roderick, Derie, Frédéric, Dexter, Jason, Duvert, Gilles, Ebert, Monica, Eckart, Andreas, Eisenhauer, Frank, Michael, Esselborn, Fédou, Pierre, Finger, Gert, Garcia, Paulo, Garcia Dabo, Cesar Enrique, Garcia Lopez, Rebeca, Gendron, Eric, Genzel, Reinhard, Gillessen, Stefan, Conté, Frédéric, Gordo, Paulo, Grould, Marion, Groözinger, Ulrich, Guieu, Sylvain, Haguenauer, Pierre, Hans, Olivier, Haubois, Xavier, Haug, Marcus, Haussmann, Frank, Henning, Thomas, Hippler, Stefan, Horrobin, Matthew, Huber, Armin, Hubert, Zoltan, Hubin, Norbert, Hummel, Christian, Jakob, Gerd, Janssen, A., Jochum, Lieselotte, Jocou, Laurent, Kaufer, Andreas, Kellner, Stefan, Kendrew, Sarah, Kern, Lothar, Kervella, Pierre, Kiekebusch, Mario, Klein, Ralf, Kok, Y., Kolb, Johan, Kulas, Martin, Lacour, Sylvestre, Lapeyrère, Vincent, Lazareff, Bernard, Le Bouquin, Jean-Baptiste, Léna, Pierre, Lenzen, Rainer, Levêque, Samuel, Lippa, Magdalena, Magnard, Yves, Mehrgan, Leander, Mellein, Marcus, Merand, Antoine, Moreno-Ventas, Javier, Moulin, Thibaut, Müller, Eric, Müller, Fredrich, Neumann, Udo, Oberti, Sylvain, Ott, Thomas, Pallanca, Laurent, Panduro, Johana, Pasquini, Luca, Paumard, Thibaut, Percheron, Isabelle, Perraut, Karine, Perrin, Guy, Pflüger, Andreas, Pfuhl, Olivier, Duc, Thanh Phan, Plewa, Philipp, Popovic, Dan, Rabien, Sebastian, Ramirez, Andres, Ramos, Jose, Rau, Christian, Riquelme, Miguel, Rohloff, Ralf-Rainer, Rousset, Gérard, Sanchez-Bermudez, Joel, Scheithauer, Sylvia, Schöller, Marcus, Schuhler, Nicolas, Spyromilio, Jason, Straubmeier, Christian, Sturm, Eckhard, Suarez, Marco, Tristram, Konrad, Ventura, Noel, Vincent, Frédéric, Waisberg, Idel, Wank, Imke, Weber, J., Wieprecht, Ekkehard, Wiest, Michael, Wiezorrek, Erich, Wittkowski, Markus, Woillez, Julien, Wolff, Burkhard, Yazici, Senol, Ziegler, Denis, Zins, Gérard, Amorim, A., Anugu, N., Ávila, G., Clenet, Y., Coudé Du Foresto, V., de Zeeuw, P., Deen, C., Esselborn, M., Dabo, C, Gonte, F., Grözinger, U., Henning, Th, Le Bouquin, J.-B, Lèna, P., Lévêque, S., Mérand, A., Muller, E., Muller, F., Phan Duc, T., Ramírez, A., Garcia Dabo, E., Henning, Th., Le Bouquin, B., Plewa, M., European Southern Observatory (ESO), CENTRA, Universidade de Lisboa, CENTRA, Universidade do Porto, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), 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), Observatoire Astronomique de l'Université de Genève (ObsGE), Université de Genève (UNIGE), Max-Planck-Institut für Astronomie (MPIA), Max-Planck-Gesellschaft, Max Planck Institute for Extraterrestrial Physics (MPE), Leiden Observatory [Leiden], Universiteit Leiden [Leiden], ONERA - The French Aerospace Lab [Châtillon], ONERA, Physikalisches Institut [Köln], Universität zu Köln, Max Planck Institute for Radio Astronomy, Department of Physics [Berkeley], University of California [Berkeley], University of California-University of California, European Space Agency (ESA), European Southern Observatory [Santiago] (ESO), Institute Patology and Imunology Molecular, Fac Ciencias, Universidade do Porto [Porto], Brain Mind Institute (BMI - EPFL), Ecole Polytechnique Fédérale de Lausanne (EPFL), Technische Universität Dresden (TUD), Departamento de Control Automático (CINVESTAV-IPN), Center for Research and Advanced Studies of the National Polytechnic Institute (CINVESTAV-IPN), Universidade do Porto, 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), 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]), ONERA-Université Paris Saclay (COmUE), GRAVITY Collaboration, European Southern Observatory ( ESO ), 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 Diderot - Paris 7 ( UPD7 ) -Centre National de la Recherche Scientifique ( CNRS ), Institut de Planétologie et d'Astrophysique de Grenoble ( IPAG ), Observatoire des Sciences de l'Univers de Grenoble ( OSUG ), 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 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 ) -Centre National de la Recherche Scientifique ( CNRS ), Observatoire Astronomique de l'Université de Genève ( ObsGE ), Université de Genève ( UNIGE ), Max-Planck-Institut für Astronomie ( MPIA ), Max Planck Institute for Extraterrestrial Physics ( MPE ), ONERA - The French Aerospace Lab ( Chatillon ), Max Planck Institute for Radio Astronomy, Bonn, European Space Agency ( ESA ), Universidad de Santiago de Chile [Santiago] ( USACH ), European Southern Observatory [Santiago] ( ESO ), University of Porto, Center for Brain Simulation, Ecole Polytechnique Fédérale de Lausanne, Technische Universität Dresden ( TUD ), Departamento de Control Automático ( CINVESTAV-IPN ), Center for Research and Advanced Studies of the National Polytechnic Institute ( CINVESTAV-IPN ), Universidade do Porto = University of Porto, Université de Genève = University of Geneva (UNIGE), Universiteit Leiden, Universität zu Köln = University of Cologne, University of California [Berkeley] (UC Berkeley), University of California (UC)-University of California (UC), and Agence Spatiale Européenne = European Space Agency (ESA)

Subjects
[ SPI.SIGNAL ] Engineering Sciences [physics]/Signal and Image processing, Astrophysics, ÉTOILE DOUBLE, OPTIQUE ADAPTATIVE, 01 natural sciences, law.invention, law, Astrophysics::Solar and Stellar Astrophysics, INSTRUMENTATION OPTIQUE, INSTRUMENTATION, instrumentation: interferometers, 010303 astronomy & astrophysics, Physics, Galaxy: center, Galactic Center, Astrophysics::Instrumentation and Methods for Astrophysics, Astrometry, [PHYS.PHYS.PHYS-SPACE-PH]Physics [physics]/Physics [physics]/Space Physics [physics.space-ph], [ PHYS.PHYS.PHYS-SPACE-PH ] Physics [physics]/Physics [physics]/Space Physics [physics.space-ph], quasars: emission lines, Interferometry, EMISSION LINE, Closure phase, binaries: symbiotic, Astrophysics::Earth and Planetary Astrophysics, [ SPI.OPTI ] Engineering Sciences [physics]/Optics / Photonic, Astrophysics - Instrumentation and Methods for Astrophysics, [SPI.SIGNAL]Engineering Sciences [physics]/Signal and Image processing, CENTER, INTERFEROMETRIE GRANDE BASE, FOS: Physical sciences, stars: pre-main sequence, instrumentation: adaptive optics, QUASAR, 010309 optics, Telescope, 0103 physical sciences, Angular resolution, INTERFEROMETERS, Instrumentation and Methods for Astrophysics (astro-ph.IM), CENTRE GALACTIQUE, Astrophysics::Galaxy Astrophysics, ADAPTIVE OPTICS, Very Large Telescope, Astronomy and Astrophysics, First light, GALAXY, Space and Planetary Science, [SPI.OPTI]Engineering Sciences [physics]/Optics / Photonic, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract

GRAVITY is a new instrument to coherently combine the light of the European Southern Observatory Very Large Telescope Interferometer to form a telescope with an equivalent 130 m diameter angular resolution and a collecting area of 200 m$^2$. The instrument comprises fiber fed integrated optics beam combination, high resolution spectroscopy, built-in beam analysis and control, near-infrared wavefront sensing, phase-tracking, dual beam operation and laser metrology [...]. This article gives an overview of GRAVITY and reports on the performance and the first astronomical observations during commissioning in 2015/16. We demonstrate phase tracking on stars as faint as m$_K$ ~ 10 mag, phase-referenced interferometry of objects fainter than m$_K$ ~ 15 mag with a limiting magnitude of m$_K$ ~ 17 mag, minute long coherent integrations, a visibility accuracy of better than 0.25 %, and spectro-differential phase and closure phase accuracy better than 0.5{\deg}, corresponding to a differential astrometric precision of better than 10 microarcseconds ({\mu}as). The dual-beam astrometry, measuring the phase difference of two objects with laser metrology, is still under commissioning. First observations show residuals as low as 50 {\mu}as when following objects over several months. We illustrate the instrument performance with the observations of archetypical objects for the different instrument modes. Examples include the Galactic Center supermassive black hole and its fast orbiting star S2 for phase referenced dual beam observations and infrared wavefront sensing, the High Mass X-Ray Binary BP Cru and the Active Galactic Nucleus of PDS 456 for few {\mu}as spectro-differential astrometry, the T Tauri star S CrA for a spectro-differential visibility analysis, {\xi} Tel and 24 Cap for high accuracy visibility observations, and {\eta} Car for interferometric imaging with GRAVITY., Comment: Accepted for publication in A&A, 23 pages, 23 figures, corresponding author: F. Eisenhauer

Published
2017
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8. To be or not to be Asymmetric? VLTI/MIDI and the Mass-loss Geometry of AGB Stars

Author

Paladini, Claudia, Klotz, Daniela, Sacuto, Stephane, Lagadec, Eric, Wittkowski, Markus, Richichi, Andrea, Hron, Josef, Jorissen, Alain, Groenewegen, Martin A. T., Kerschbaum, Franz, Verhoelst, Tijl, Rau, Gioia, Olofsson, Hans, Zhao-Geisler, Ronny, and Matter, Alexis

Subjects
Astrophysics::Instrumentation and Methods for Astrophysics, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Astrophysics::Galaxy Astrophysics
Abstract

The Mid-infrared Interferometric instrument (MIDI) at the Very Large Telescope Interferometer (VLTI) has been used to spatially resolve the dust-forming region of 14 asymptotic giant branch (AGB) stars with different chemistry (O-rich and C-rich) and variability types (Miras, semi-regular, and irregular variables). The main goal of the programme was to detect deviations from spherical symmetry in the dust-forming region of these stars. All the stars of the sample are well resolved with the VLTI, and five are asymmetric and O-rich. This finding contrasts with observations in the near-infrared, where the C-rich objects are found to be more asymmetric than the O-rich ones. The nature of the asymmetric structures so far detected (dusty discs versus blobs)remains uncertain and will require imaging on milli-arcsecond scales., Published in The Messenger vol. 168, pp. 28-31, June 2017.

Published
2017
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9. VLTI Imaging of a High-Mass Protobinary System: Unveiling the Dynamical Processes in High-Mass Star Formation

Author

Kraus, Stefan, Kluska, Jacques, Kreplin, Alexander, Bate, Matthew, Harries, Timothy, Hofmann, Karl-Heinz, Hone, Edward, Monnier, John, Weigelt, Gerd, Anugu, Narsireddy, De Wit, Willem-Jan, and Wittkowski, Markus

Subjects
010504 meteorology & atmospheric sciences, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics::Earth and Planetary Astrophysics, 010303 astronomy & astrophysics, 01 natural sciences, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences
Abstract

High-mass stars exhibit a significantly higher multiplicity frequency than low-mass stars, likely reflecting differences in how they formed. Theory suggests that high-mass binaries may form by the fragmentation of self-gravitational discs or by alternative scenarios such as disc-assisted capture. Near-infrared interferometric observations reveal the high-mass young stellar object IRAS 17216-3801 to be a close high-mass protobinary with a separation of 0.058 arcseconds (~ 170 au). This is the closest high-mass protobinary system imaged to date. We also resolve near- infrared excess emission around the individual stars, which is associated with hot dust in circumstellar discs. These discs are strongly misaligned with respect to the binary separation vector, indicating that tidal forces have not yet had time to realign. We measure a higher accretion rate towards the circumsecondary disc, confirming a hydrodynamic effect where the secondary star disrupts the primary star’s accretion stream and effectively limits the mass that the primary star can accrete. NACO L′-band imaging may also have resolved the circumbinary disc that feeds the accretion onto the circumstellar discs. This discovery demonstrates the unique capabilities of the VLTI, creating exciting new opportunities to study the dynamical processes that govern the architecture of close multiple systems., Published in The Messenger vol. 170, pp. 45-49, December 2017.

Published
2017
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10. Mass Losing Asymptotic Giant Branch Stars and Supergiants

Author

Whitelock, Patricia A., Boyer, Martha, Höfner, Susanne, Wittkowski, Markus, Zijlstra, Albert A., and Feiden, Gregory A.

Subjects
stellar parameters, FOS: Physical sciences, interferometry, binary stars, radio, models, Astrophysics - Solar and Stellar Astrophysics, Supergiants, infrared, Astrophysics::Solar and Stellar Astrophysics, pulsation, dust, Astrophysics::Earth and Planetary Astrophysics, AGB stars, Astrophysics::Galaxy Astrophysics, Solar and Stellar Astrophysics (astro-ph.SR)
Abstract

This paper presents a summary of four invited and twelve contributed presentations on asymptotic giant branch stars and red supergiants, given over the course of two afternoon splinter sessions at the 19th Cool Stars Workshop. It highlights both recent observations and recent theory, with some emphasis on high spatial resolution, over a wide range of wavelengths. Topics covered include 3D models, convection, binary interactions, mass loss, dust formation and magnetic fields., Comment: To appear in the proceedings of the 19th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun; 19 pages and 20 figures

Published
2016
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11. The potential of near-infrared high-resolution studies on the field of galaxies in the young universe

Author

Wittkowski, Markus

Subjects
Astrophysics (astro-ph), Astrophysics::Instrumentation and Methods for Astrophysics, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Astrophysics::Galaxy Astrophysics
Abstract

So far, high resolution techniques on the one hand provide morphological information on bright nearby objects. On the other hand, telescopes with large collecting areas allow us to detect very faint and distant objects, but not to obtain a spatial resolution which is sufficient for detailed morphological studies. Currently, the construction of large optical and infrared interferometers like the Keck Interferometer, the Very Large Telescope Interferometer (VLTI) and the Large Binocular Telescope Interferometer (LBTI) is in progress. These instruments will simultaneously provide larger collecting areas and higher spatial resolutions than current instruments. Thus, they might enable for the first time near-infrared studies of galaxies in the young universe with an absolute spatial resolution as available today only for the closest galaxies. Using recent results in the field of high resolution studies of nearby galaxies, a rough idea of what might be expected to be observed is given. The concepts of the forthcoming interferometers is reviewed and technical aspects that are essential for observations of distant galactic centers are discussed. An outlook is given on which observational tasks can be addressed to these instruments and how the results will increase our knowledge in the field of the evolution of galaxies and the universe., Comment: 9 pages, to appear in proceedings of JSPS/DFG Japan-German Seminar 2001 "Studies of Galaxies in the Young Universe with New Generation Telescopes", July 24-28, Sendai, Japan

Published
2001
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12. Tomography of evolved star atmospheres

Author

Kravchenko, Kateryna, Van Eck, Sophie, Chiavassa, Andréa, Jorissen, Alain, Godefroid, Michel, Perrin, Guy, Wittkowski, Markus, and Freytag, Bernd

Subjects
Star atmospheres, spectroscopy, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, interferometry, Red supergiant stars, Asymptotic giant branch stars, Astrophysics - Solar and Stellar Astrophysics, radiative transfer, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Astrophysics::Galaxy Astrophysics, Astrophysique, Solar and Stellar Astrophysics (astro-ph.SR)
Abstract

Cool giant and supergiant stars are among the largest and most luminous stars in the Universe and, therefore, dominate the integrated light of their host galaxies. These stars were extensively studied during last few decades, however their relevant properties like photometric variability and mass loss are still poorly constrained. Understanding of these properties is crucial in the context of a broad range of astrophysical questions including chemical enrichment of the Universe, supernova progenitors, and the extragalactic distance scale. Atmospheres of giant and supergiant stars are characterized by complex dynamics due to different interacting processes, such as convection, pulsation, formation of molecules and dust, and the development of mass loss. Current 1D/3D dynamical model atmospeheres are able to simulate these processes and produce a good agreement with the observed spectral features of evolved stars. However, the models lack constraints and need to be confronted to observables. Dynamical processes in stellar atmospheres impact the formation of spectral lines producing their asymmetries and Doppler shifts. Thus, by studying the line-profile variations on spatial and temporal scales it is possible to reconstruct atmospheric motions in evolved stars. As will be shown in this thesis, a tomographic method is an ideal technique for this purpose. The tomographic method is based on construction and cross-correlation of spectral templates (masks) with observed or synthetic stellar spectra in order to recover velocity fields at different optical depths in the stellar atmosphere.The first part of the thesis further improves the original implementation of the tomographic method. This improvement involves the computation of the contribution function in order to correctly determine an optical depth of formation of spectral lines. The tomographic method is, then, fully validated by applying it to a stellar convection simulation of a red supergiant star and correctly recovering its velocity field throughout the atmosphere. The second part of the thesis applies the tomographic method to the red supergiant star μ Cep in order to constrain its atmospheric motions and relate them to photometric variability. A phase lag (hysteresis) between the effective temperature and the radial velocity variations is revealed with timescales of a few hundred days, similar to photometric ones. A comparison to a stellar convection simulation of a red supergiant star indicates that hysteresis loops are linked to the stochastic shocks generated and shaped by the underlying large-scale convection and may be responsible for photometric variations in μ Cep. The third part of the thesis applies the tomographic method to spectro-interferometric observations of the Mira-type star S Ori. The uniform-disk angular diameters measured at wavelengths contributing to the tomographic masks increase with decrease of an optical depth probed by the masks. This validates the capability of the tomographic method to probe distinct geometrical depths in the stellar atmosphere. The last part of the thesis applies the tomograhic method to the Mira-type star RY Cep and compares the results to those obtained for μ Cep in this thesis. The comparison reveals differences in their behavior in the temperature-velocity plane pointing to the posibility to differentiate between Mira-type and red supergiant stars from their spectroscopic signatures., Doctorat en Sciences, info:eu-repo/semantics/nonPublished

Published
2022
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