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Postdoc in gyrochronology and asteroseismology

The “Stellar Ages and Galactic Evolution” (SAGE www.mps.mpg.de/sage) independent research group based at the Max Planck Institute for Solar System Research (MPS www.ps.mpg.de) in Göttingen invites experts in gyrochronology and asteroseismology to apply for a postdoctoral position funded by an ERC starting grant. The position is for 2 years starting October 1, 2016 or earlier. Payment and benefits are according to German TVÖD.

The Position

The SAGE research group is a vibrant and young group consisting of experts in asteroseismology, stellar evolution, Milky Way structure and computer science. The group now seeks an expert in gyrochronology and asteroseismology to derive (differential) rotational profiles and ages of main-sequence stars, subgiants and red-giant stars in the framework of the ERC starting grant “Stellar Ages”. For further information and inquiries about this project please contact Saskia Hekker (Hekker_at_mps.mpg.de).

Your profile

We seek a motivated candidate with a PhD in astronomy and knowledge and skills in gyrochronology and asteroseismology. Applicants should have published research results in high-impact journals, demonstrated creativity, independence, high motivation, good communication skills, and has the ability to work independently as well as with other members of our research group.

Your application

Please send your application including
• a cover letter summarizing your qualifications and your motivation to work on the project,
• a CV with a full publication list, and
• names and contacts of two to three references.
The application should be submitted electronically as one file to Saskia Hekker (Hekker_at_mps.mpg.de) with “Job application ERC-Gyro” in the subject line. Applications received by July 1, 2016 will receive full consideration. Review of the applications will continue until a suitable candidate is found.
The Max Planck Society is committed to employing more handicapped individuals and especially encourages them to apply. The Max Planck Society seeks to increase the number of women in those areas where they are under-represented and therefore explicitly encourages women to apply.

Closing Date: 01.07.2016

Contact:  Saskia Hekker, hekker_at_mps.mpg.de

Max Planck Institute for Solar System Research
Justus-von-Liebig Weg 3
37077 Göttingen
Germany

SAGE group, Max Planck Institute for Solar System Research
Goettingen, Germany

Staff scientist in solar/stellar physics – can become permanent

The Faculty of Physics at the University of Goettingen invites applications for a Staff scientist in solar/stellar physics at the Institute for Astrophysics. The staff scientist position is full time and for an initial period of two years, after which it can become permanent subject to a successful performance review. The position should be filled in 2016; the start date is negotiable. Remuneration: pay grade E13 TV-L on the German civil service salary scale.

Your duties

• Contribute to teaching activities as defined in Section 31 of the Higher Education Act of Lower Saxony (NHG) and to the organization of examinations.

• Carry out support tasks for the physics faculty, for example, administer computer systems at the Institute for Astrophysics.

• Perform research in one or more of the following research areas:

– solar and/or stellar physics;
– helioseismology and/or asteroseismology;
– exoplanets and their host stars;
– computational physics;
– applied mathematics.

Your profile

• A proven track record of scientific achievements

• A genuine interest in teaching

• Excellent communication skills and the ability to work in a team

• A doctoral degree

The University of Goettingen is an equal opportunities employer and places particular emphasis on fostering career opportunities for women. Qualified women are therefore strongly encouraged to apply as they are under-represented in this field. The University firmly intends to raise the number of disabled persons in its employment. In the case of equally qualified applicants, disabled persons will be preferentially considered.

Please send your application with the usual documents by 1st July 2016 to sekr@astro.physik.uni-goettingen.de as a single PDF file. For questions please contact gizon@astro.physik.uni-goettingen.de. Please see the University of Goettingen’s website for the full job advertisement: http://www.uni-goettingen.de/de/305402.html?cid=11614

Goettingen calls itself ‘City of Science’. Its international academic reputation attracts researchers and students from all over the world, making this town a lively centre in the heart of Germany. To find out more about living in Goettingen, see http://www.uni-goettingen.de/downloads/BKM/INTBrosch2012/index.htm

Closing Date: 01.07.16

University of Goettingen
Goettingen, Germany
Please contact: gizon@astro.physik.uni-goettingen.de.

The Seismic+ Portal is online!

The growing amount of seismic data available from space missions (SOHO, CoRoT, Kepler, SDO,…), and also from ground-based observations (GONG, Bison, Song, ground-based large programmes…), is boosting solar and stellar structure and evolution studies. While it is now possible to have new insights into stellar structure and evolution, the Sun remains more than ever a crucial reference and a precious guideline for numerous stellar studies.

New scientific perspectives emerge for a broad scientific community, e.g. to characterize stellar populations in our Galaxy or to characterize planetary systems by giving model-independent estimates of global properties of stars such as mass, radius, and surface gravity within several percent accuracy, as well as to constrain the age.

Seismic data become a ‘plus’ to be used in conjunction with data of various types and from various sources, e.g. space seismic archives and ground-based spectroscopic surveys, or solar seismic data to be analyzed ‘as a star’ and used as a reference in stellar studies.

The intention of the Seismic+ portal is to bridge over various data types and over different scientific communities.

You can find the Seismic+ Portal by following this link.

SOLARNET III / HELAS VII / SpaceInn Conference – “The Sun, the stars, and solar-stellar relations”

The 3rd SOLARNET / 7th HELAS / SpaceInn international conference “The Sun, the stars, and Solar-stellar relations” will take place in Freiburg (Germany) between 31 August – 4 September 2015, organized by the Kiepenheuer-Institut für Sonnenphysik (KIS).

SOLARNET (High-resolution Solar Physics Network) is an international project promoted by the European Association for Solar Telescopes (EAST) and funded by the European Commission FP7.

HELAS is the European Helio- and Asteroseismology Network, which aims at coordinating the activities of the research groups active in helio-and asteroseismology.

The purpose of this conference is to discuss the latest questions and results in solar and stellar physics. Solar and stellar seismology will be one particular focus but contributions on all aspects of solar-stellar relations will be welcome.

We aim to establish links and synergies between the day- and night-time fields of astrophysics.

In detail the following topics will be addressed in individual sessions as showed in the Scientific Program.

Furthermore new and upcoming projects and missions shall be presented.

Graduate students and early-career postdocs are particularly invited to participate in the conference to present their research work and to meet and discuss with their more senior colleagues.

A limited amount of financial resources shall be available to grant travel support.

A dedicated website for this event can be found at http://www.iac.es/congreso/solarnet-3meeting/

The conference poster can be downloaded  (7MB) here.

Contact: mroth(at)kis.uni-freiburg.de

1 Postdoctoral and 1 PhD positions in stellar magnetohydrodynamics at CEA, Saclay, France

Closing Date: 31.06.2015

Job opening for one post-doctoral and one PhD positions in MHD of stellar interiors, tidal interactions in stellar systems, and dynamical stellar evolution in Service d’Astrophysique at CEA Saclay (France) in support of the ERC project SPIRE

We invite applications for one 4-year post-doctoral position and one 3-year PhD position in stellar magnetohydrodynamics, dynamical stellar evolution and ab-initio modelling of tidal interactions in star-planet and multiple star systems in support of the European ERC-CoG project SPIRE (Stars: dynamical Processes driving tidal Interactions, Rotation and Evolution).

The objective of the project is to contribute to interpret new ground breaking high-resolution observations provided by asteroseismology on stellar interiors and their dynamics and planetary system discoveries and characterization (e.g. CoRoT and Kepler and in a near future CHEOPS, TESS, SPIRou, PLATO). To reach this ambitious objective, it is necessary to develop now new frontier theoretical and numerical long-term evolution models of rotating magnetic stars and of their systems. In this framework, the members of the SPIRE project will develop new state-of-the-art equations, prescriptions, and scaling laws that describe coherently dynamical mechanisms that transport angular momentum and drive tidal dissipation in stars using advanced ab-initio semi-analytical modelling and numerical simulations. They will be implemented in the new generation dynamical stellar evolution code STAREVOL and N-body code ESPER to provide realistic integrated and coupled models for the long-term evolution of stars and of their systems, which cannot be directly simulated in 3D yet.

The positions will be held in Service d’Astrophysique (SAp) at CEA-Saclay (France). SAp is a world class astrophysical and space science department with more than 180 faculty and staff members, studying stellar and planetary physics, astrophysical fluid and plasma dynamics, planets and stars formation, high energy astrophysics, galactic and extragalactic astrophysics, cosmology. The PI of the SPIRE project, Dr. S. Mathis, is permanent researcher in the Laboratory of Dynamics of Stars and their Environment. The team hosts recognized experts in stellar systems who carry research at the forefront of their theoretical and numerical modelling and characterization thanks to asteroseismology. CEA possesses large computer facilities and expertise that represent a strong asset for the development of (MHD) numerical simulations and advanced stellar modelling.

The growing SPIRE team focuses mostly on ab-initio semi-analytical and numerical modelling of the exchanges of angular momentum within stars and their planetary systems and of their impact on their evolution. The successful candidates will benefit from our existing and productive scientific national and international collaborations in stellar and planetary physics, in the study of Star-Planet Interactions, and in fluid dynamics.

The positions:

Position A 3-year PhD position in stellar magnetohydrodynamics: the successful candidate will collaborate with the PI, Dr. A.-S. Brun and members of the SPIRE project to establish new semi-analytical and numerical models of the excitation, propagation, and damping/resonances/instabilities of internal gravity waves in differentially rotating magnetic stars along their evolution. Obtained equations, prescriptions and scaling laws will be implemented in complete 2D secular transport equations for angular momentum, heat and chemicals in stars, which will be implemented in the dynamical stellar evolution code STAREVOL used by SPIRE members. Applicants should have a Master in astrophysics, geophysics, fluid dynamics or plasma physics.

Position B 4-year post-doc position in modelling tidal flows and their dissipation in stars: the successful candidate will collaborate with the PI and the members of the team to establish new ab-initio semi-analytical and numerical models of tidal torques/dissipation in rotating magnetic stars. She/he will study tidally excited magneto-gravito-inertial waves and their interactions with mean flows, turbulence and magnetic fields in stellar interiors. She/he will contribute to provide prescriptions and scaling laws that will be implemented in STAREVOL and ESPER. The required profile is a candidate with a strong background in theoretical and numerical astrophysical/geophysical fluid dynamics or/and stellar/planetary physics.

For the post-doc position, applicants should have a PhD in astrophysical/geophysical fluid dynamics, theoretical stellar or planetary physics, fluid mechanics or plasma physics. They should have a very good record of research and publications and real interest in theoretical and numerical astrophysics, fluid dynamics and applied mathematics.

These positions funded for at least 3 years (and up to 4 years) by the European Commission via the grant ERC-CoG SPIRE will be reniewed on a yearly basis depending on scientific progress and achievement. The salary will be commensurate to the competitive standard scale for PhD and post-doctoral researchers at CEA. A minimum of 5,000 Euros per year of travel money for each position will also be provided, in addition to the usual funding support of any French institution.

The preferred starting date is 1 September 2015, but can be discussed depending on the availability of selected candidates. Candidates are thus requested to indicate their preferred starting date in their application.

The application for the PhD position must include
– A Curriculum Vitae
– A letter detailing your motivation and qualifications for the position (maximum 1 page)
– Two letters of references. The letters are to be submitted separately to Dr. Stéphane Mathis.

The application for the post-doctoral position must include
– A Curriculum Vitae including publication list
– A statement of research experience, interests and future plans (maximum 3 pages)
– A letter detailing your motivation and qualifications for the position and your career objectives (maximum 1 page)
– Three letters of references. The letters are to be submitted separately to Dr. Stéphane Mathis.

Applications sent before 15 May 2015 for the post-doctoral positions and before 20 April 2015 for the PhD position will be given top priority but applications will be considered until positions are filled.

Laboratory Dynamics of Stars and their Environment CEA/DSM/IRFU/SAp & UMR AIM Paris-Saclay
CEA, Saclay, France
Please contact: stephane.mathis@cea.fr

Peak-bagging in Helio- and Asteroseismology

We are pleased to announce the SpaceInn Group Meeting Workshop “Peak-bagging in Helio- and Asteroseismology” to be held in Tenerife on 11-13 March 2014. The aim of the workshop is to bring together active researches in these domains to contribute to define and to establish the proper methodology to achieve the goals associated with some of the deliverables of the “Global Helioseismology” work package of the Spaceinn Project.

The workshop will take place in the Sandos San Blas Hotel Reserva Ambiental, in the village of San Miguel de Abona, South of Tenerife.

The workshop webpage can be found at: http://www.iac.es/congreso/spaceinn-wp41/

On this webpage you can find more information on the scientific program, the venue, and how to register and make the hotel reservation. We hope to welcome many of you in Tenerife!

In case of questions, you can contact to us at spaceinn_wp41 (at) iac (dot) es

Important dates:

  • February 10, 2014: deadline for hotel reservation and registration
  • March 11-13, 2014: SpaceInn Workshop 4.1

Testing excitation models of rapidly oscillating Ap stars with interferometry

Authors. Cunha, M. S.; Alentiev, D.; Brandão, I. M.; Perraut, K.

Journal. Monthly Notices of the Royal Astronomical Society, Volume 436, Issue 2, p.1639-1647

Abstract. Rapidly oscillating Ap stars are unique objects in the potential they offer to study the interplay between a number of important physical phenomena, in particular, pulsations, magnetic fields, diffusion and convection. Nevertheless, the simple understanding of how the observed pulsations are excited in these stars is still in progress. In this work, we perform a test to what is possibly the most widely accepted excitation theory for this class of stellar pulsators. The test is based on the study of a subset of members of this class for which stringent data on the fundamental parameters are available thanks to interferometry. For three out of the four stars considered in this study, we find that linear, non-adiabatic models with envelope convection suppressed around the magnetic poles can reproduce well the frequency region where oscillations are observed. For the fourth star in our sample no agreement is found, indicating that a new excitation mechanism must be considered. For the three stars whose observed frequencies can be explained by the excitation models under discussion, we derive the minimum angular extent of the region where convection must be suppressed. Finally, we find that the frequency regions where modes are expected to be excited in these models are very sensitive to the stellar radius. This opens the interesting possibility of determining this quantity and related ones, such as the effective temperature or luminosity, from comparison between model predictions and observations, in other targets for which these parameters are not well determined.

Links. MNRAS, NASA ADS, arXiv

The fundamental parameters of the roAp star 10 Aquilae

Authors. Perraut, K.; Borgniet, S.; Cunha, M.; Bigot, L.; Brandão, I.; Mourard, D.; Nardetto, N.; Chesneau, O.; McAlister, H.; ten Brummelaar, T. A.; Sturmann, J.; Sturmann, L.; Turner, N.; Farrington, C.; Goldfinger, P. J.

Journal. Astronomy & Astrophysics, Volume 559, id.A21, 8 pp

Abstract. Context. Owing to the strong magnetic field and related abnormal surface layers existing in rapidly oscillating Ap (roAp) stars, systematic errors are likely to be present when determining their effective temperatures, which potentially compromises asteroseismic studies of this class of pulsators.
Aims: Using the unique angular resolution provided by long-baseline visible interferometry, our goal is to determine accurate angular diameters of a number of roAp targets, so as to derive unbiased effective temperatures (Teff) and provide a Teff calibration for these stars.
Methods: We obtained long-baseline interferometric observations of 10 Aql with the visible spectrograph VEGA at the combined focus of the CHARA array. We derived the limb-darkened diameter of this roAp star from our visibility measurements. Based on photometric and spectroscopic data available in the literature, we estimated the star’s bolometric flux and used it, in combination with its parallax and angular diameter, to determine the star’s luminosity and effective temperature.>
Results: We determined a limb-darkened angular diameter of 0.275 ± 0.009 mas and deduced a linear radius of R = 2.32 ± 0.09 R. For the bolometric flux we considered two datasets, leading to an effective temperature of Teff = 7800 ± 170 K and a luminosity of L/L = 18 ± 1 or Teff = 8000 ± 210 K and L/L = 19 ± 2. Finally we used these fundamental parameters together with the large frequency separation determined by asteroseismic observations to constrain the mass and the age of 10 Aql, using the CESAM stellar evolution code. Assuming a solar chemical composition and ignoring all kinds of diffusion and settling of elements, we obtained a mass M/M ~ 1.92 and an age of ~780 Gy or a mass M/M ~ 1.95 and an age of ~740 Gy, depending on the derived value of the bolometric flux.
Conclusions: For the first time, thanks to the unique capabilities of VEGA, we managed to determine an accurate angular diameter for a star smaller than 0.3 mas and to derive its fundamental parameters. In particular, by only combining our interferometric data and the bolometric flux, we derived an effective temperature that can be compared to those derived from atmosphere models. Such fundamental parameters can help for testing the mechanism responsible for the excitation of the oscillations observed in the magnetic pulsating stars.

Based on observations made with the VEGA/CHARA spectro-interferometer.

Links. A&A, NASA ADS, arXiv

Asteroseismic fundamental properties of solar-type stars observed by the NASA Kepler Mission

Authors.W. J. Chaplin, S. Basu, D. Huber, A Serenelli, L. Casagrande, V. Silva Aguirre, W. H. Ball, O. L. Creevey, L. Gizon, R. Handberg, C. Karoff, R. Lutz, J. P. Marques, A. Miglio, D. Stello, M. D. Suran, D. Pricopi, T. S. Metcalfe, M. J. P. F. G. Monteiro, J. Molenda-Zakowicz, T. Appourchaux, J. Christensen-Dalsgaard, Y. Elsworth, R. A. Garcia, G. Houdek, H. Kjeldsen, A. Bonanno, T. L. Campante, E. Corsaro, P. Gaulme, S. Hekker, S. Mathur, B. Mosser, C. Regulo, D. Salabert

Journal.The Astrophysical Journal Supplement, Volume 210, Issue 1, article id. 1, 22 pp.

Abstract.We use asteroseismic data obtained by the NASA Kepler Mission to estimate the fundamental properties of more than 500 main-sequence and sub-giant stars. Data obtained during the first 10 months of Kepler science operations were used for this work, when these solar-type targets were observed for one month each in a survey mode. Stellar properties have been estimated using two global asteroseismic parameters and complementary photometric and spectroscopic data. Homogeneous sets of effective temperatures, T_eff, were available for the entire ensemble from complementary photometry; spectroscopic estimates of T_eff and [Fe/H] were available from a homogeneous analysis of ground-based data on a subset of 87 stars. We adopt a grid-based analysis, coupling six pipeline codes to eleven stellar evolutionary grids. Through use of these different grid-pipeline combinations we allow implicitly for the impact on the results of stellar model dependencies from commonly used grids, and differences in adopted pipeline methodologies. By using just two global parameters as the seismic inputs we are able to perform a homogenous analysis of all solar-type stars in the asteroseismic cohort, including many targets for which it would not be possible to provide robust estimates of individual oscillation frequencies (due to a combination of low S/N and short dataset lengths). The median final quoted uncertainties from consolidation of the grid-based analyses are for the full ensemble (spectroscopic subset) approximately 10.8&#37 (5.4&#37) in mass, 4.4&#37 (2.2&#37) in radius, 0.017 dex (0.010 dex) in log g, and 4.3&#37 (2.8&#37) in mean density. Around 36&#37 (57 &#37) of the stars have final age uncertainties smaller than 1 Gyr. These ages will be useful for ensemble studies, but should be treated carefully on a star-by-star basis. Future analyses using individual oscillation frequencies will offer significant improvements on up to 150 stars, in particular for estimates of the ages, where having the individual frequency data is most important.

Links. IOP Science, NASA ADS, arXiv

Low-amplitude rotational modulation rather than pulsations in the CoRoT B-type supergiant HD 46769

Authors. Aerts, C.; Simón-Díaz, S.; Catala, C.; Neiner, C.; Briquet, M.; Castro, N.; Schmid, V. S.; Scardia, M.; Rainer, M.; Poretti, E.; Pápics, P. I.; Degroote, P.; Bloemen, S.; Østensen, R. H.; Auvergne, M.; Baglin, A.; Baudin, F.; Michel, E.; Samadi, R.

Journal. Astronomy & Astrophysics, Volume 557, id.A114, 9 pp

Abstract. Aims: We aim to detect and interpret photometric and spectroscopic variability of the bright CoRoT B-type supergiant target HD 46769 (V = 5.79). We also attempt to detect a magnetic field in the target.
Methods: We analyse a 23-day oversampled CoRoT light curve after detrending and spectroscopic follow-up data using standard Fourier analysis and phase dispersion minimization methods. We determine the fundamental parameters of the star, as well as its abundances from the most prominent spectral lines. We perform a Monte Carlo analysis of spectropolarimetric data to obtain an upper limit of the polar magnetic field, assuming a dipole field.
Results: In the CoRoT data, we detect a dominant period of 4.84 d with an amplitude of 87 ppm and some of its (sub-)multiples. Given the shape of the phase-folded light curve and the absence of binary motion, we interpret the dominant variability in terms of rotational modulation, with a rotation period of 9.69 d. Subtraction of the rotational modulation signal does not reveal any sign of pulsations. Our results are consistent with the absence of variability in the Hipparcos light curve. The spectroscopy leads to a projected rotational velocity of 72 ± 2 km s-1 and does not reveal periodic variability or the need to invoke macroturbulent line broadening. No signature of a magnetic field is detected in our data. A field stronger than ~500 G at the poles can be excluded, unless the possible non-detected field were more complex than dipolar.
Conclusions: The absence of pulsations and macroturbulence of this evolved B-type supergiant is placed into the context of instability computations and of observed variability of evolved B-type stars.

Based on CoRoT space-based photometric data; the CoRoT space mission was developed and operated by the French space agency CNES, with the participation of ESA’s RSSD and Science Programmes, Austria, Belgium, Brazil, Germany, and Spain. Based on observations collected at La Silla Observatory, ESO (Chile) with the HARPS spectrograph at the 3.6 m telescope, under programme LP185.D-0056. Based on observations obtained with the HERMES spectrograph attached to the 1.2 m Mercator telescope, which is supported by the Fund for Scientific Research of Flanders (FWO), Belgium, the Research Council of KU Leuven, Belgium, the Fonds National de la Recherche Scientific (FNRS), Belgium, the Royal Observatory of Belgium, the Observatoire de Genève, Switzerland, and the Thüringer Landessternwarte Tautenburg, Germany. Based on observations obtained with the Narval spectropolarimeter at the Observatoire du Pic du Midi (France), which is operated by the Institut National des Sciences de l’Univers (INSU).

Links. A&A, NASA ADS, arXiv