All posts by admin

The unusual roAp star KIC 8677585

Authors. Balona, L. A. ; Catanzaro, G. ; Crause, L. ; Cunha, M. S. ; Gandolfi, D. ; Hatzes, A. ; Kabath, P. ; Uytterhoeven, K. ; De Cat, P.

Journal. Monthly Notices of the Royal Astronomical Society, Volume 432, Issue 4, p.2808-2817

Abstract. KIC 8677585 is a roAp star in the Kepler field which is unique in that there are four low-frequency variations of unknown origin in addition to more than 20 high-frequency roAp modes. We analysed all available spectroscopy and conclude that the star has a constant radial velocity and most likely not a binary. We estimate its effective temperature to be Teff = 7300 ± 200 K from high-dispersion spectra. We present an analysis of 829 d of Kepler short-cadence data which shows clear frequency and amplitude variations with a time-scale of months. The dominant low-frequency peak at 3.142 d-1 has the same frequency and amplitude variation as one of the roAp modes. We therefore conclude that the low frequencies are oscillations in the roAp star itself, but the driving mechanism is unknown. We find several frequency spacings among the roAp modes equal to the dominant low frequency, suggestive of non-linear interactions. There is also a clear spacing of 37.2 μHz which we interpret as the large separation and deduce that log g = 3.90 ± 0.03. Models with these parameters which take into account the effect of the magnetic field on the oscillations are able to reproduce the observed range of roAp frequencies, but not the observed large separation. It is found that the properties of the oscillations are sensitive to the assumed stellar parameters and that a more detailed analysis is required. The fact that low frequencies are closely coupled to the roAp frequencies calls into question our current understanding of pulsation in these stars.


Stellar Ages and Convective Cores in Field Main-sequence Stars: First Asteroseismic Application to Two Kepler Targets

Authors. V. Silva Aguirre, S. Basu, I. M. Brandão, J. Christensen-Dalsgaard, S. Deheuvels, G. Doğan, T. S. Metcalfe, A. M. Serenelli, J. Ballot, W. J. Chaplin, M. S. Cunha, A. Weiss, T. Appourchaux, L. Casagrande, S. Cassisi, O. L. Creevey, R. A. Garcia, Y. Lebreton, A. Noels, S. G. Sousa, D. Stello, T. R. White, S. D. Kawaler, H. Kjeldsen

Journal. The Astrophysical Journal, Volume 769, Issue 2, article id. 141, 17 pp. (2013)

Abstract. Using asteroseismic data and stellar evolution models we obtain the first detection of a convective core in a Kepler field main-sequence star, putting a stringent constraint on the total size of the mixed zone and showing that extra mixing beyond the formal convective boundary exists. In a slightly less massive target the presence of a convective core cannot be conclusively discarded, and thus its remaining main-sequence lifetime is uncertain. Our results reveal that best-fit models found solely by matching individual frequencies of oscillations corrected for surface effects do not always properly reproduce frequency combinations. Moreover, slightly different criteria to define what the best-fit model is can lead to solutions with similar global properties but very different interior structures. We argue that the use of frequency ratios is a more reliable way to obtain accurate stellar parameters, and show that our analysis in field main-sequence stars can yield an overall precision of 1.5%, 4%, and 10% in radius, mass, and age, respectively. We compare our results with those obtained from global oscillation properties, and discuss the possible sources of uncertainties in asteroseismic stellar modeling where further studies are still needed.

Links. The Astrophysical Journal, NASA ADSarXiv,

SPACEINN Postdoctoral Position in Helioseismology

Closing Date: October 15, 2013


The Max Planck Institute for Solar System Research (MPS) in Goettingen, Germany, invites applications for a postdoctoral position in the framework of EU FP7 Collaborative Project “Exploitation of Space Data for Innovative Helio- and Asteroseismology” (SPACEINN) comprising 17 international research institutions. The position is available immediately for a period of ca. three years. The ideal candidate is an active researcher in helioseismology familiar with SDO/HMI observations. Applications should include a CV and a short statement of research interests. Applications should be sent as a single PDF file to with the mention “SPACEINN Job” in the subject line. Applications received by 15 September 2013 will receive full consideration. Remuneration of postdoctoral scientists at the MPS is according to the German public salary scale TVoeD. The MPS is an equal opportunity employer and places particular emphasis on providing career opportunities for women.

Max-Planck-Institut für Sonnensystemforschung
Katlenburg-Lindau, Germany
Please contact:

Postdoctoral Scientist on Helioseismology at the Kiepenheuer-Institut für Sonnenphysik, Freiburg, Germany

Closing Date: September 30, 2013

Ref: PostDoc (SpaceInn)

Applications are invited for the full-time position of a post-doctoral scientist at the Kiepenheuer-Institut für Sonnenphysik (KIS), Freiburg, Germany. The position will be part of the collaborative project “Exploitation of Space Data for Innovative Helio- and Asteroseismology – SpaceInn” which is funded under EU’s Framework Programme 7 and aims at an optimal use of existing and planned data in helio- and asteroseismology (

The successful candidate will join the vibrant research group on helio- and asteroseismology led by Dr. Markus Roth within the Kiepenheuer-Institut für Sonnenphysik in Freiburg. This research group is currently composed of 2 staff scientists, 3 postdocs, 4 Phd students, 2 master students and a number of visiting scientists.

Based on the existing Fourier-Legendre analysis pipeline for helioseismic data at KIS, the successful candiate will work on improving the parameter estimation of p modes, inversions, and implementing the pipeline at the German data center for SDO hosted at the Max-Planck institute for Solar System Research in Katlenburg-Lindau.

Applicants should have a PhD in physics or astrophysics and research experience in helioseismology. Knowledge of programming computer codes and webinterfaces, as well as of helioseismic inversions are of advantage.

KIS is a Foundation of Public Law of the state of Baden-Württemberg with the mission to perform fundamental astrophysics research with an emphasis on solar physics. Current research foci include the Sun, the stars, and advanced instrumention development. KIS operates the German solar facilities at the Teide Observatory on Tenerife, including the new 1.5m Gregor solar telescope, to carry out observations at visible and near-infrared wavelengths. Further information can be obtained at the institute’s webpage (

KIS is committed to increasing the number of female scientists and therefore encourages
qualified women to apply.

The position is available immediately. Starting date can be negotiated. The initial appointment is for 2 years.

General information:
The employment, salary, and benefits are according to the rules of the “Tarifvertrag für den
öffentlichen Dienst der Länder” (collective agreement for public services of the Federal States). Full-time positions can be shared, if there is no conflict with official and legal reasons.
Severly handicapped people with equal qualifications will be employed with preference.

The application should include a curriculum vitae, university degree, PhD certificate, a list of publications, copies of three relevant publications, and a list of three potential referees.

Candidates that match the required profile will be continuously interviewed until the position is filled.

Kiepenheuer-Institut für Sonnenphysik
Freiburg, Germany
Please contact:

Research Fellowship in the field of Astero and Helio-Seismology

Closing Date: June 30, 2013

Ref: CAUP2013-05UnI-BI

The Centro de Astrofisica da Universidade do Porto (CAUP) opens a call for one Research Fellowship to work in solar and stellar physics including the exploitation of seismic space data. The position is offered with financial support provided by the project ‘Exploitation of Space Data for Innovative Helio- and Asteroseismology (SPACEINN)’ with financial support provided by European Commission. The researcher will be integrated in the team “Origin and Evolution of Stars and Planets”.

Centro de Astrofisica da Universidade do Porto (CAUP)

Please contact: