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SOLARNET III / HELAS VII / SpaceInn Conference
The Sun, the stars, and solar-stellar relations Free Conference is closed
Conference is closed
solarnet3.2015
Hosted by Markus Roth
Affiliation Kiepenheuer-Institut fuer Sonnenphysik
Freiburg, Germany
30.08.2015 - 03.09.2015

Organizing institutions
Kiepenheuer-Insitution for Solar Physics
Main category Natural Sciences (Astrophysics and Astrononmy)
Conference/Workshop objectives

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.
A variety of topics of solar and stellar physics will be addressed in individual sessions as detailed 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.

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

 

Local organizing committee
Wiebke Glißmann;Markus Roth (Chair); Bettina Schäfer  
Scientific organizing committee (SOC)

Markus Roth (KIS)
Rafael Garcia (CEA)

Sessions
  • Session I: Solar and stellar observations
  • Session II: Solar and stellar modelling
  • Session III: Solar and stellar seismology
  • Session IV: In memory of Jean-Paul Zahn
  • Session V: Solar and stellar activity
  • Splinter Session: Waves inside Stars: Theory, Simulations, Observational Signatures, and Lab Experiments
  • Splinter Session: Open-access tools for local helioseismology provided by SpaceInn
  • Splinter Session: Comparing and Validating Meridional Flow Derivations in the Solar Convection Zone
  • Splinter Session: Meridional flow, α effect, single vs multiple dynamo: addressing open issues in solar/stellar dynamo with p-mode parameters
  • Poster session: Solar physics
  • Poster session: Helioseismology
  • Poster session: Asteroseismology
  • Poster session: Projects
Programme
Invited speakers Thomas Ayres; Sarbani Basu; Svetlana Berdyugina; Maria Bergemann; Matt Browning; Guy Davis; Sebastien Deheuvels; Louise Harra; Laurene Jouve; Lucia Kleint; Zarzalt Magic; Stéphane Mathis; Ian Roxburgh; Ariane Schad; Alina Donea
Important dates

May 31, 2015: End of early registration
 

May 15, 2015: Deadline for applications for financial support
 

July 10, 2015: Abstract submission deadline
 

 

Registration and payment information The registration includes conference material, all lunches, coffee breaks, one organised tour, and one conference dinner. Early registration until June 1, 2015: € 350,- per person Late registration after June 1, 2015: € 400,- per person Registration for accompanying persons: € 100,- per person (tour and conference dinner) Credit card payment Payment can be done in two ways: 1.) Credit card: Only VISA or MASTERCARD are acepted. Please print the CREDIT CARD PAYMENT FORM, fill in all applicable fields with capital letters, scan it, and send by fax to +34 922 605 210 (preferable) or email to solarnet@iac.es In case you submit the form via fax, please send also an email to LOC at glissmann@kis.uni-freiburg.de 1.) Wire transfer: Please contact the LOC at glissmann@kis.uni-freiburg.de for the bank coordinates. PLEASE NOTE: No payment will be accepted at the conference!
Conference venue Freiburg, Germany
Hotel information A block reservation of 100 rooms has been made in the Novotel on the group code “SolarNet Meeting”. The following rooms (including breakfast) can be booked based on availability: Standard single room €119,- Standard double room for single occupancy €134,- Superior double room for single occupancy €154,- For booking a room please contact the hotel directly. The code for obtaining the group prices is: “SolarNet Meeting”. Deadline for hotel booking with the discounted rate: June 30, 2015. Novotel Freiburg Am Konzerthaus Tel.: 0049 761 3889 0 FAX: 0049 761 3889 100 Mail: H5383(at)accor.com
Travel information

There are several airports nearby Freiburg:

 
1. Basel/Mulhouse/Freiburg, from there you can continue to Freiburg train station either by bus or by train (1 hour travel distance).

2. Strassbourg, from there you can continue to Freiburg by train going via Offenburg (2 hours travel distance).

3. Frankfurt, from there you can continue to Freiburg by the fast ICE trains (2.5 hours travel distance).

4. Zurich, from there you can continue via trains (2.5 hours travel distance).

For international arrivals, i.e. from outside Europe, the best options are flying to Frankfurt or Zurich and continuing from there by train.

Germany offers a good network of train connections. Major cities in Germany including Freiburg are connected by the fast ICE trains. The German (and European) train schedule is available at: http://www.bahn.de

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SOLARNET - High Resolution Solar Physics Network

Session: Poster session: Projects

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Date of upload:
28.08.2015
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Caption:
Video on Solar Physics at the IAC with English Subtitles El IAC cuenta sus líneas de investigación en cinco vídeos. "Física Solar" es el primero de los audiovisuales producidos por este centro astrofísico con financiación del programa Severo Ochoa.
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Markus Roth

Session: Session I: Solar and stellar observations

685 views
Date of upload:
31.08.2015
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Abstract:
These are the slides of the opening of the Solarnet III / HELAS VII / SpaceInn Conference in Freiburg, August 31, 2015.
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Louise Harra

Session: Session V: Solar and stellar activity

846 views
Date of upload:
03.09.2015
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Abstract:
A review of solar flares
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Paul Rajaguru

Session: Session III: Solar and stellar seismology

604 views
Date of upload:
03.09.2015
Co-author:
H.M. Antia (Tata Institute of Fundamental Research, Mumbai, India)
Abstract:
We present results from time-distance helioseismic measurements of meridional circulation in the solar convection zone using 4 years of Doppler velocity observations by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). We show, by taking into account the limitations of decreasing signal-to-noise in the travel time measurements of acoustic waves that sample deeper layers and through an in-built mass conservation constraint in the inversion scheme, that the return flow that closes the meridional circulation is possibly below a depth of about 0.77 R_sun. We discuss the significance of this result in relation to other helioseismic inferences published recently and possible reasons for the differences in the results. We also discuss the implications of our results for the dynamics of solar interior and popular solar dynamo models.
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Laurene Jouve

Session: Session II: Solar and stellar modelling

579 views
Date of upload:
03.09.2015
Co-author:
C. Hung, A.S. Brun, A. Fournier, O. Talagrand
Abstract:
We will review recent progress made in modeling solar-type stars in 2D and 3D in the recent years. In particular, we will focus on advances in our understanding of the dynamo processes in such astrophysical objects and the necessary ingredients to reproduce what is found in the observations. We will also present recent attempts to introduce such observational data into multi-D MHD models. The idea is to implement data assimilation techniques to solar physics in order to have some tools to give tentative predictions of future solar activity.
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Frank Hill

Session: Session I: Solar and stellar observations

738 views
Date of upload:
03.09.2015
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Abstract:
GONG (Global Oscillation Network Group) is now 20 years old and continues to reliably provide data for the international helioseismology community. In addition the role of GONG has expanded to provide data as input to a number of space weather forecasting systems. This talk will give a summary of the status of GONG, its future plans, and a brief review of some recent science results.
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Rudolf Komm

Session: Session III: Solar and stellar seismology

649 views
Date of upload:
03.09.2015
Co-author:
Rachel Howe, Frank Hill
Abstract:
We study the solar-cycle variation of the zonal and meridional flow in the near-surface layers of the solar convection zone from the surface to a depth of about 16 Mm. We have analyzed Dopplergrams obtained with the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO), the Global Oscillation Network Group (GONG),and the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) with a dense-pack ring-diagram analysis. The three data sets combined cover almost two solar cycles. The zonal and meridional flows vary with the solar cycle. Their amplitude variation tracks the mean latitude of activity and appears about three years before magnetic activity is visible in synoptic maps of the solar surface. We focus on the variation of the zonal and meridional flows, including their long-term variation at mid- and low-latitudes using GONG and MDI data and their variation at the high latitudes that are now accessible using HMI data. We will present the latest results.
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Vincent Prat

Session: Session IV: In memory of Jean-Paul Zahn

741 views
Date of upload:
03.09.2015
Co-author:
François Lignières (IRAP), Jérôme Ballot (IRAP)
Abstract:
Seismology of intermediate-mass and massive stars is limited by our lack of understanding of the effect of fast rotation on gravity modes. In particular, in this regime perturbative methods are unable to identify observed modes. We therefore develop an asymptotic theory for adiabatic gravito-inertial modes in uniformly rotating stars. We first derived a generalized dispersion equation taking the Coriolis force and the centrifugal deformation into account. The corresponding ray dynamics allowed us to explore the structure of the phase space thanks to a ray-tracing code. We observed three coexisting types of structures: (i) nearly integrable structures similar to non- rotating structures, (ii) island chains around stable periodic orbits, (iii) large chaotic zones. These three different types of structures are expected to give three different families of modes.
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Ângela R. G. Santos

Session: Session III: Solar and stellar seismology

604 views
Date of upload:
03.09.2015
Co-author:
M. S. Cunha, P. P. Avelino, W. J. Chaplin, T. L. Campante
Abstract:
The frequencies of the solar oscillations are known to vary in phase with the Sun's activity level. The solar cycle is accompanied by changes in the overall magnetic field as well as in the area covered by active regions, which can affect the wave propagation, hence, the oscillation frequencies, through direct and indirect effects. However, the importance of the different contributions is not well established. With this in mind, we developed an empirical model to estimate the spot-induced frequency shifts. The model assumes the sunspot properties, such as the time dependent latitudinal distribution and area and a characteristic induced phase difference that represents the local impact of a spot on the wave. We have applied our model to the sunspot daily records (from NGDC/NOAA) and synthetic sunspot data. By comparing the frequency shifts obtained with our model using real sunspot data with those observed, we are able to estimate that the contribution from spots to the observed frequency shifts is about 30%.
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Conny Aerts

Session: Splinter Session: Waves inside Stars: Theory, Simulations, Observational Signatures, and Lab Experiments

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Date of upload:
04.09.2015
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Abstract:
Waves inside Stars: Theory, Simulations, Observational Signatures, and Lab Experiments Splinter session, Monday 31 August, 9h25 - 12h30, during SOLARNET III / HELAS VII / SpaceInn Conference "The Sun, the stars, and solar-stellar relations" http://www.iac.es/congreso/solarnet-3meeting/ Organisers: Tamara Rogers (Newcastle University, UK) Conny Aerts (Leuven University, B) Abstract: Waves are as ubiquitous in stars as they are on Earth. Just as on Earth, waves can transport angular momentum and mix species within stellar interiors, steering their rotational and chemical evolution. Waves also set up standing modes which can be observed through helio- and asteroseismology. Helioseismology has revolutionized our picture of the Sun, constraining the internal rotation profile and convective undershooting in the solar interior. Asteroseismology is not far behind, recently constraining core-envelope differential rotation and core convective overshooting in more massive stars. Indeed, the observations of waves through helio- and asteroseismology places the tightest constraints on the dynamical evolution those same waves induce. This 3-hour splinter session aims to bring together researchers doing theory, simulations, and observations of waves in stars (gravity, pressure and mixed) with the hope that the synergy between the three (often disparate) fields could lead to tests and comparisons which would further our understanding of stellar interiors. Moreover, we include also studies of wave generation by convection in laboratory experiments to search for connections between those and stellar physics. We begin this session with four short talks on each of the sub-topics and will then continue with a guided discussion on how these fields can work together to advance our understanding. Programme: Monday 31 August, 09:25 - 12:30 09:25 Welcome 09:30 - 10:00 Theory: Stephane Mathis (Saclay, France) 10:00 - 10:30 Simulations: Tami Rogers (Newcastle, UK) 10:30 - 11:00 Coffee Break 11:00 - 11:15 Observational Signatures: Conny Aerts (Leuven, B) 11:15 - 11:30 Lab Experiments: Santiago Andres Triana (Leuven, B) 11:30 - 12:15 Guided discussion, participants are encouraged to bring 1 slide 12:15 - 12:30 Summary of Synergies & Future Steps
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Rudolf Komm

Session: Session III: Solar and stellar seismology

544 views
Date of upload:
04.09.2015
Co-author:
Sushant Tripathy, Rachel Howe, Frank Hill
Abstract:
The active region 10486 that produced the Halloween flares in 2003 initiated our interest in the kinetic helicity of subsurface flows associated with active regions. This lead to the realization that the helicity of subsurface flows is related to the flare activity of active regions. Eleven years later, a similarly enormous active region (12192) appeared on the solar surface. We plan to study the kinetic helicity of the subsurface flows associated with region 12192 and compare it to that of region 10486. For 10486, we have analyzed Dopplergrams obtained with the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO) and the Global Oscillation Network Group (GONG) with a dense-pack ring-diagram analysis. For 12192, we have analyzed Dopplergrams from GONG and the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). We will present the latest results.
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Damien Przybylski

Session: Session III: Solar and stellar seismology

778 views
Date of upload:
04.09.2015
Co-author:
Sergiy Shelyag and Paul Cally
Abstract:
Measurements made around active regions are complicated by magneto-acoustic mode-conversion and changes in the radiative properties of magnetic field concentrations. Forward modelling has been performed using the SPARC numerical code in a semi-empirical magneto-hydrostatic model of a large-scale solar magnetic field mimicking a sunspot. The 6173 A absorption line used by the HMI instrument has been synthesized at various positions on the solar disk. Using the response of this spectrum at different observational inclinations slow modes are seen in the sunspot umbra.
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Frederic Baudin

Session: Session V: Solar and stellar activity

575 views
Date of upload:
04.09.2015
Co-author:
John Leibacher, Maria-Cristina Rabello Soares, Florent Baudin
Abstract:
Flares have been suspected to excite solar p-modes since the 1970s. More recently, Karoff & Kjeldsen (2008) investigated flare excitation of global oscillations while Maurya et al. (2009, 2014) did a local analysis (ring diagrams) of flaring regions. We investigate these previous results by applying similar methods with the aim of confirming (or not) these results. Particular attention is paid to possible biases in the analysis. This lead us to infirm some of the previous results.
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Tamara Rogers

Session: Splinter Session: Waves inside Stars: Theory, Simulations, Observational Signatures, and Lab Experiments

587 views
Date of upload:
05.09.2015
Co-author:
Abstract:
Short description of numerical work on waves in massive stars.
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Volkmar Holzwarth

Session: Session II: Solar and stellar modelling

554 views
Date of upload:
07.09.2015
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Abstract:
Close binary stars with late spectral-type components, such as RS CVn- or BY Dra-systems, are among the magnetically most active stellar objects known. The magnetic flux generated in the outer convection zone of these rapidly rotating cool stars leads after emergence at the stellar surface to a plethora of activity signatures, which cover large time-, spatial-, and spectral-ranges. Direct observations of coronal magnetic fields are, however, hardly possible and even in the case of the Sun limited to snapshots of localised regions. Investigations focusing on the structure and evolution of large-scale magnetic fields thus frequently apply approximation techniques which are based on the extrapolation of observed magnetic field distributions on the stellar surface into upper atmospheric layers. Here, the potential field source surface approximation technique, which was originally developed for the case of the Sun and later applied to active single stars as well, has been extended to the case of binary systems to investigate their joint magnetospheres and, in particular, the properties of inter-connecting magnetic field structures. The extended modelling technique is described before its capabilities are demonstrated on the basis of a "solar-twin" system, for which synoptic magnetic maps of the Sun observed during different phases of its activity cycle are used. The connectivity of closed coronal loops, 'open' field regions, and inter-connecting field structures is determined for different combinations of solar synoptic maps (e.g. active-active, active-inactive) and compared with the joint magnetospheres of the system V4046Sgr.
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Vincent Böning

Session: Session III: Solar and stellar seismology

682 views
Date of upload:
07.09.2015
Co-author:
Markus Roth, Jason Jackiewicz
Abstract:
We present the current status of an undergoing validation of a recently developed model for computing spherical Born approximation sensitivity functions for flows. In a first step, power spectra and reference cross-correlations from the model and a simulation of Hartlep et al. (2013) are matched. Some difficulties in obtaining such a match are discussed. In a second step, travel times from the forward model and from the simulation, which includes a standard meridional flow profile, are to be compared. The analysis procedure including the use of phase-speed filters is identical to the one employed in Jackiewicz et al. (2015). Furthermore, we present a novel approach for a fast computation of integrated sensitivity functions which can be used for interpreting rotationally symmetric flows such as differential rotation and meridional flow.
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Markus Roth

Session: Splinter Session: Meridional flow, α effect, single vs multiple dynamo: addressing open issues in solar/stellar dynamo with p-mode parameters

829 views
Date of upload:
07.09.2015
Co-author:
Abstract:
This is a short description on how to upload the conference contributions.
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ehsan moravveji

Session: Session III: Solar and stellar seismology

726 views
Date of upload:
07.09.2015
Co-author:
Conny Aerts, Peter Papics, Santiago Triana
Abstract:
Thanks to the unprecedented high quality space photometry provided by CoRoT and Kepler missions, our view on stellar oscillations in B-type stars and the physics of the upper HRD is progressively improving. O- and B-type stars harbor a fully mixed convective cores, and a radiative envelope. However, the interface between these two layers -- the so-called overshooting layer -- is not understood from first principles. Thus, the width and the mixing efficiency of the overshooting layer is always treated by simplistic schemes like step-function or exponentially diffusive mixing prescriptions. We modelled two rich main sequence pulsators observed by Kepler and CoRoT which also turn out to be very slowly rotating pulsating B stars. They are KIC 10526294 and HD 50230, respectively. Based on forward seismic modelling, we derive the width of the overshooting layer on top of their receding cores. Additionally, we show that extra diffusive mixing of 100 to 10 000 cm$^2$ sec$^{-1}$ in the radiative envelope of these two stars is essential to better fit their observed g-mode frequencies. We also compare the classical step-function versus exponential diffusive overshoot. The diffusive overshooting prescription outperforms the other to fit the observed frequencies by a factor 2 to 3 (in $\chi^2$ sense). The derived values for the overshooting and diffusive mixing coefficients are weakly dependent on the choice of opacities and chemical mixtures, and are considered robust constraints.
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Jacobo Varela

Session: Session II: Solar and stellar modelling

853 views
Date of upload:
08.09.2015
Co-author:
S. Brun
Abstract:
The aim of the present study is to characterize the effect of the rotation rate in building magnetic field via dynamo action in solar-like stars. We use the code ASH to model the convective dynamo for solar-like stars at various rotation rates and hence Rossby numbers. We find that stable magnetic configuration without cycling evolution; with steady low latitude magnetic field wreaths are found for slowly rotating cases with large Rossby number. For models rotating faster with a low Rossby number, the convective dynamo shows a cycling activity, leading to systematic pole inversion. We also note that a topology change of the stellar magnetic field occurs going from a dipolar-like to a quadrupolar-like structure when the system magnetic energy drops during the cyclic activity, in good agreement with our star the Sun.
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Dean-Yi Chou

Session: Splinter Session: Comparing and Validating Meridional Flow Derivations in the Solar Convection Zone

536 views
Date of upload:
08.09.2015
Co-author:
Abstract:
See the file.
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Dean-Yi Chou

Session: Session III: Solar and stellar seismology

617 views
Date of upload:
08.09.2015
Co-author:
Abstract:
See the file.
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George Angelou

Session: Session III: Solar and stellar seismology

773 views
Date of upload:
08.09.2015
Co-author:
Saskia Hekker, Elisabeth Guggenberger, Nathalie Themessl
Abstract:
Over 35 years ago, it was proposed that there exists diagnostic potential in combining the small and large frequency separations for solar-like oscillators. Since then, we have been spoilt with a plethora long-timeseries photometric light curves from which individual stochastic oscillation modes can be extracted. These light curves allow the separations to be determined en masse and in power spectra with relatively low signal-to-noise ratios. The small-frequency separation in low-mass main-sequence stars and in subgiants is sensitive to the molecular weight gradient in the inner regions whilst the large-frequency separation is indicative of the mean density of the star. We investigate how accurately these parameters must be determined in order to place constraints on stellar parameters such as mass and age. We discuss some difficulties associated with calculating the necessary large grids of models (with different input physics) as well as the degeneracy that exists in later evolutionary phases.
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Aditi Sood

Session: Session II: Solar and stellar modelling

661 views
Date of upload:
09.09.2015
Co-author:
Eun-jin Kim
Abstract:
We for the first time propose a spin-down model where the loss of angular momentum by magnetic fields is dynamically treated, instead of being kinematically prescribed. To this end, we evolve stellar rotation and magnetic field simultaneously over the stellar evolution time by incorporating the nonlinear feedback mechanisms on rotation and magnetic fields and examine the behaviour of rotation rate $\Omega$ with time $t$, magnetic field strength $|B|$ and frequency of magnetic field $\omega_{cyc}$ with rotation rate $\Omega$. Initially, rotation rate is found to decrease very rapidly with time until there is a sudden transition from fast to slow spin down of stars. The dependence of rotation rate on time illustrates exponential spin-down for rapid rotators and power law spin-down for slow rotators. For fast rotators, the strength $|B|$ is found to saturate for large $\Omega$ while for slow rotators, $|B|$ increases almost linearly with $\Omega$. The analysis of the local frequency of magnetic fields reveals the existence of the two (active and inactive) branches of magnetic fields for stars with different frequencies $\omega_{cyc}$ which have different scalings with rotation rate $\Omega$: the active and inactive branches with power law scaling exponents 0.85 and 1.16, respectively. The transition from fast to slow rotators occurs very rapidly with the disappearance of the active branch. .The Vaughan-Preston gap is consistently explained in our model by the shortest spin-down timescale in this transition from fast to slow rotators. All these results successfully reproduce the key observations and capture the V-P gap in a self-contained model.
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Ariane Schad

Session: Session III: Solar and stellar seismology

671 views
Date of upload:
09.09.2015
Co-author:
M. Roth
Abstract:
I review and discuss recent helioseismic measurements of the meridional circulation and solar rotation from analysis of mode eigenfunction perturbations. Results obtained from analysis of MDI data covering 2006-2010 and from HMI data covering 2010-1014 are shown. The method is verified using numerical simulations. The results are compared to other helioseismic measurements of the meridional flow.
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Sanjay gosain

Session: Session I: Solar and stellar observations

1016 views
Date of upload:
09.09.2015
Co-author:
Jack Harvey
Abstract:
SOLIS stands for Synoptic Optical Long-term Investigations of the Sun. Daily fulldisk magnetic fields measurements of the Sun are being done for several decades at NSO Kittpeak. The SOLIS/VSM instrument replaced earlier instruments at Kitt Peak. The current SOLIS/VSM instrument has capability to make full Stokes polarimetry in photospheric lines, however, for chromosphere only longitudinal polarimetry exists. With the recent progress in non-LTE inversions of the chromospheric spectra it was decided that a full Stokes polarimeter needs to be developed. Based on similar design to photospheric modulator we have developed a separate modulator for chromospheric full Stokes measurements using Ca II 854.2 nm line. We will present design and performance of the new modulator and possibly sample observations.
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Sanjay gosain

Session: Session I: Solar and stellar observations

861 views
Date of upload:
09.09.2015
Co-author:
Markus Roth, Frank Hill, Michael Thompson
Abstract:
Synoptic observations of the Sun are very important to understand the long term behavior of the solar activity cycle. Our current understanding solar magnetic cycle is rather in its infancy, as can be inferred from our very poor prediction for the strength of solar cycle 24, based on various dynamo models. Solar magnetism is at the heart of all solar activity and therefore it is important to understand what parameters govern the magnetic cycle in the Sun. An important parameter that is realized more recently is the internal dynamics, i.e., profile of solar internal rotation and nature of large scale meridional flows. Therefore, it is important to study the solar interior by making use of helioseismology. Ground based helioseismology networks such as GONG are now quite few decades old and its possible failure poses risk to the continuity of solar oscillation data. Hence, a next generation of synoptic network SPRING is being proposed and is currently under design study. We will present science requirements and the details of the SPRING network.
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Anne-Marie Broomhall

Session: Session III: Solar and stellar seismology

641 views
Date of upload:
10.09.2015
Co-author:
Abstract:
Low-frequency solar p modes have long lifetimes and, therefore, narrow peaks in frequencypower spectra. This allows their frequencies to be obtained very precisely, making them useful inputs for inversions of the solar interior. However, these low-frequency p modes have limited sensitivity to the solar core, which is still relatively poorly constrained. Mixed and gravity modes, on the other hand, are far more sensitive to core regions. Low-frequency p modes, mixed modes, and gravity modes are all difficult to detect because they have relatively small amplitudes and because they are swamped by solar noise from, for example, convection. We have developed statistical techniques to try and uncover these low signal-to-noise modes. We have then used these techniques to search for previously undetected low-frequency oscillations in BiSON and GONG data, considering the data sets both individually and contemporaneously. To uncover the modes we have developed both frequentist and Bayesian approaches. The developed techniques are very flexible and could be useful for asteroseismic studies as well as helioseismology.
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Ralph Neuhaeuser

Session: Session I: Solar and stellar observations

628 views
Date of upload:
10.09.2015
Co-author:
Abstract:
Presentation at CID:solarnet3.2015
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mutlu yildiz

Session: Session III: Solar and stellar seismology

586 views
Date of upload:
10.09.2015
Co-author:
Abstract:
Low amplitude is the defining characteristic of solar-like oscillations. The space projects Kepler and CoRoT give us a great opportunity to successfully detect such oscillations in numerous targets. Achievements of asteroseismology depend on new discoveries of connections between the oscillation frequencies and stellar properties. In the previous studies, the frequency of the maximum amplitude and the large separation between frequencies were used for this purpose. In the present study, we confirm that the large separation between the frequencies has two minima at two different frequency values. These are the signatures of the He {\small II} ionization zone, and as such have very strong diagnostic potential. We relate these minima to fundamental stellar properties such as mass, radius, luminosity, age and mass of convective zone. For mass, the relation is simply based on the ratio of the frequency of minimum $\Delta \nu$ to the frequency of maximum amplitude. These frequency comparisons can be very precisely computed, and thus the mass and radius of a solar-like oscillating star can be determined to high precision. We also develop a new asteroseismic diagram which predicts structural and evolutionary properties of stars with such data. We derive expressions for mass, radius, effective temperature, luminosity and age in terms of purely asteroseismic quantities. For solar-like oscillating stars, we now will have five very important asteroseismic tools ( two frequencies of minimum $\Delta \nu$, the frequency of maximum amplitude, and the large and small separations between the oscillation frequencies) to decipher properties of stellar interior astrophysics.
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Gaël Buldgen

Session: Session III: Solar and stellar seismology

611 views
Date of upload:
14.09.2015
Co-author:
Marc-Antoine Dupret, Daniel Roy Reese
Abstract:
Constraining additional mixing processes is a central problem in stellar physics. Indeed, their impact on determined stellar ages is non-negligible and thus strongly affects our studies of stellar evolution, galactic history, and exoplanetary systems. However, the quality of the Kepler data allows us to use new seismic tools to constrain these processes. In this talk, we will show a particularly efficient method for constraining chemical mixing in stellar interiors using custommade structural integrated quantities. These quantities are designed to probe particular regions of the stellar interior and are estimated via the SOLA inversion method (Pijpers and Thompson 1994). They help us determine the values of parameters describing extra mixing processes. Inversions of such quantities have been originally described for the mean density in Reese et al. (2012) and have been extended to the acoustic radius and a first indicator of core conditions in Buldgen et al. (2015). A more efficient indicator for core conditions has now been derived and successfully tested using test cases similar to the 16Cyg binary system (Buldgen et al. in prep.). In this talk, we will show how our technique applies to the system 16Cyg and constrains additional mixing processes using the above structural indicators. Additional indicators and further studies will lead to seismically constrained chemical profiles for stars observed by Kepler, thereby helping us to disentangle the problem of additional mixing processes and ultimately to provide better stellar ages.
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Kaori Nagashima

Session: Session III: Solar and stellar seismology

641 views
Date of upload:
14.09.2015
Co-author:
Kaori Nagashima, Laurent Gizon, Aaron C. Birch, Damien Fournier
Abstract:
In current time-distance helioseismology analyses the (phase) travel time is commonly used. However, other than the travel time, there are parameters of the cross-covariance functions of the solar oscillation field that are affected by solar interior structure and dynamics. Including these parameters in helioseismology analyses might improve the analyses. Therefore, here we focus on one such parameter, the amplitude. We formulate a two-parameter fit of the cross-covariance function in the regime where the amplitude and travel-time differences of the cross-covariance function are small, and measure amplitudes as well as travel times in several areas on the Sun. We find that the amplitude of the center-to-annulus cross-covariance function in the quiet Sun shows the supergranulation pattern, although the amplitude is noisier than the travel times; the out-in amplitude difference shows positive correlation with the out-in travel-time difference. We also detect significant amplitude reduction due to sunspots, which is consistent with Liang et al. (2013).
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Vigeesh Gangadharan

Session: Splinter Session: Open-access tools for local helioseismology provided by SpaceInn

629 views
Date of upload:
24.09.2015
Co-author:
H.-P. Doerr, K. Glogowski, and M. Roth
Abstract:
Fourier-Hankel/Legendre analysis is one of the helioseismic techniques employed to infer the internal properties of the Sun. It has been successfully applied to study p-mode interaction with sunspots and to measure sub-surface meridional flow. As part of SpaceInn project, we have implemented a new Fourier-Hankel/Legendre analysis module on the SDO/HMI JSOC data-analysis pipeline. We will present the details of the module and some preliminary results. We will also discuss on its applicability to meridional flow, differential rotation measurements and active region seismology.
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Manfred Schüssler

Session: Session I: Solar and stellar observations

815 views
Date of upload:
05.10.2015
Co-author:
J. Jiang and R. H. Cameron
Abstract:
The ongoing 11-year cycle of solar activity is considerably less vigorous than the three cycles before. It was preceded by a very deep activity minimum with a low polar magnetic flux, the source of the toroidal field responsible for solar magnetic activity in the subsequent cycle. Simulation of the evolution of the solar surface field shows that the weak polar fields and thus the weakness of the present cycle 24 are mainly caused by a number of bigger bipolar regions with a ‘wrong’ (i.e., opposite to the majority for this cycle) orientation of their magnetic polarities in the North- South direction, which impaired the growth of the polar field. These reg ions had a particularly strong effect since they emerged within ±10° latitude from the solar equator.
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Manfred Schüssler

Session: Session II: Solar and stellar modelling

978 views
Date of upload:
05.10.2015
Co-author:
R.H. Cameron
Abstract:
Hale’s polarity laws for sunspot groups, the helioseismic determination of differential rotation in the convection zone, and the success of surface flux transport models in reproducing the observed evolution of large-scale solar surface fields, together with a simple mathematical argument, yield compelling evidence that the large-scale solar dynamo operates according to the scenario originally envisaged by H.W. Babcock and R. Leighton in the 1960s. The polar fields represent THE poloidal flux from which the toroidal flux emerging in sunspot groups is wound up by (mainly latitudinal) differential rotation. The polar fields themselves result from tilted sunspot groups while small-scale magnetic features ("turbulence") do not provide a significant contribution.
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Sarbani Basu

Session: Session III: Solar and stellar seismology

628 views
Date of upload:
07.10.2015
Co-author:
Abstract:
The seismic study of the Sun and other stars offers a unique window into the interior of these stars. Helioseismic data have allowed us to determine the structure and dynamics of the Sun very precisely. In fact the high-precision data allow us to use the Sun as a laboratory to study properties of matter. Asteroseismology, the seismic study of other stars, has made tremendous progress in recent years because of missions such as CoRoT and Kepler. We are beginning to be able to use asteroseismic data to study the interiors of other stars. I discuss how and what we have learned about the Sun using helioseismic data, and how we have modified the techniques to make inferences about other stars and what we have learned about them so far.
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Sebastien Deheuvels

Session: Session IV: In memory of Jean-Paul Zahn

576 views
Date of upload:
20.10.2015
Co-author:
Abstract:
It is notoriously difficult to measure how the interior of stars rotate. So far, this has hindered our progress in stellar modeling because rotation is expected to play a central role in the evolution of stars. The inversion of the internal rotation profile of the Sun obtained from helioseismology in the 90's has revolutionized the field and shown that an efficient and yet unknown mechanism that transports angular momentum operates in the Sun. The space missions CoRoT and Kepler, launched in 2006 and 2009 respectively, have finally made it possible to probe the internal rotation of stars other than the Sun using seismology. In this review talk, we give an overview of the results that were obtained so far, which cover an ever growing part of the HR diagram, from the main sequence (inversions of the rotation profile are starting to be obtained for A, F, and B-type hybrid pulsators) to subdwarf B stars and white dwarfs. A special attention will be given to red giants, in which the detection of so-called mixed modes has made it possible to measure the core rotation rate in several hundreds of targets and to quantify radial differential rotation from the subgiant phase to the core-helium burning phase. These exciting results are giving new momentum to theoretical works tackling the question of angular momentum transport in stars by providing unprecedented observational constraints. We briefly discuss the results of some of the latest studies.
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Benard Nsamba

Session: Poster session: Asteroseismology

771 views
Date of upload:
16.08.2016
Co-author:
M. J. P. F. G. Monteiro, T. L. Campante, D. R. Reese, T. R. White, A. Garc\'{i}a Hern\'{a}ndez, C. Jiang
Abstract:
The detection and analysis of oscillations in binary star systems is critical in understanding stellar structure and evolution. This is because such systems have the same initial chemical composition and age. Solar-like oscillations have been detected in both components of the asteroseismic binary HD 176465 by Kepler (White et al., 2016). This study presents an independent modelling of the two stars in this binary system. Stellar models generated using MESA (Modules for Experiment in Stellar Astrophysics) were fitted to both the observed individual frequencies and some spectroscopic parameters. The individual theoretical oscillation frequencies for the corresponding stellar models were obtained using GYRE as the pulsation code. A Bayesian approach was applied to find the Probability Distribution Functions of the stellar parameters using AIMS (Asteroseismic Inference on Massive Scale) as the optimization code. The age of the individual stars was found to agree with that obtained by White et al., (2016) of about 3.0 $\pm$ 0.5 Gyr old.
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SOLARNET - High Resolution Solar Physics Network

Session: Poster session: Projects

838 views
Date of upload:
27.08.2015
Co-author:
Alberto Escobar, Jesús Burgos, Manuel Collados
Abstract:
As a part of the SOLARNET project, the Transnational Access and Service Programme supports the access of the European solar physics community to some of the best European telescopes. To enhance the efficiency of data usage, external observers will receive also support for postfactum reduction of data, while standard pipelines are not fully developed, with the aim of providing them science-ready data. A successful Programme, which will bring together researchers of different nationalities, forms the basis for a long-term perspective of solar physics in Europe and for the operation of the European Solar Telescope, when it become a reality.
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Ariane Schad

Session: Poster session: Projects

1293 views
Date of upload:
20.07.2015
Co-author:
Abstract:
SOLARNET III / HELAS VII / SpaceInn Conference "The Sun, the stars, and solar-stellar relations" Freiburg, August 31-September 4, 2015 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. Contact: mroth(at)kis.uni-freiburg.de
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René Kiefer

Session: Poster session: Asteroseismology

996 views
Date of upload:
01.09.2015
Co-author:
Ariane Schad, Wiebke Herzberg, and Markus Roth
Abstract:
Solar-like oscillations exhibit a regular pattern of frequencies. This pattern is dominated by the small and large frequency separations between modes. The accurate determination of these parameters is of great interest, because they give information about e.g. the evolutionary state and the mass of a star. Here, we present a robust method to determine the large and small frequency separations for time series with low signal-to-noise ratio. For this purpose, we analyse a time series of the star KIC 5184732 from the NASA Kepler satellite by employing a combination of Fourier and Hilbert transform. We use the analytic signal of the filtered time series to compute the signal envelope. Spectral analysis of the signal envelope then reveals frequency differences of dominant modes in the periodogram of the stellar time series. With this method, the large frequency separation $\Delta\nu$ can be extracted from the envelope spectrum even for data of poor signal-to-noise ratio. A modification of the method allows for an overview of regularities in a periodogram.
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René Kiefer

Session: Poster session: Helioseismology

857 views
Date of upload:
01.09.2015
Co-author:
Rudi Komm, Frank Hill
Abstract:
The properties of solar acoustic oscillations are known to vary with the solar cycle. With 20 years of continuous observations by GONG, we are now in the position to carry out a comparison of the variation of the p mode parameters between the last two solar cycles. We present results of our analyses of the widths, amplitudes, areas (width $\times$ amplitude), and background amplitudes of solar p modes, as well as the corresponding physical quantities for modes of harmonic degree $10\leq l \leq 150$ of the global solar oscillations. We investigate the variation of these parameters for different ranges of mode frequency and harmonic degree. The fractional change in mode widths is largest for modes in the frequency range 2400-3300 $\mu$Hz, regardless of harmonic degree, with an amplitude of $\sim 10\%$ between solar minimum and maximum. The fractional change in mode amplitude exhibits a peak-to-peak amplitude of $\sim 30\%$ over solar cycle 23. Also, we find hysteresis in mode amplitudes over cycle 23 for some combinations of mode frequencies and harmonic degree. The physical quantities which correspond to the mode parameters (mean square velocity power, total mode energy, mode energy supply rate) are investigated as a function of time for different ranges of harmonic degree. We find that the mode energy supply rate decreased by $\sim 20\%$ over the last 20 years.
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René Kiefer

Session: Poster session: Asteroseismology

1344 views
Date of upload:
01.09.2015
Co-author:
Ariane Schad, and Markus Roth
Abstract:
Several hundred stars were observed in the short cadence mode of the Kepler satellite during the nominal mission phase. This generated a large pool of data which can provide insight into the characteristics of stellar activity cycles of solar-type stars through the methods of asteroseismology. From helioseismology it is known that the frequencies of solar acoustic oscillations (p modes) are positively correlated with the solar magnetic activity cycle. Evidence for a similar behaviour in the p modes of a star, which was observed by the CoRoT satellite, was provided by [1]. This showed that it is feasible to trace activity cycles of stars in their p mode frequencies. We analyse the Kepler time series of a set of solar-type stars with the aim to find signatures of stellar magnetic activity. We divide the time series of each star into shorter sub-series in order to analyse the temporal evolution of the p mode frequencies. The sub-series’ periodograms are cross-correlated to retrieve the shift of p mode frequencies over time. The errors on the shifts are computed by a resampling approach of the periodogram. We find significant frequency shifts, indicating stellar magnetic activity, for all stars we investigated. For the most prominent example, KIC 8006161, we find that, not unlike in the solar case, frequency shifts are smallest for the lowest and largest for the highest p mode frequencies.
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Markus Roth

Session: Poster session: Projects

1202 views
Date of upload:
16.06.2015
Co-author:
The SpaceInn Board
Abstract:
The European Helio- and Asteroseismology Network (HELAS) has initiated the follow-up project "SpaceInn - Exploitation of Space Data for Innovative Helio- and Asteroseismolgoy" with the mission to build on the existing European strength in the field of time-domain stellar physics. SpaceInn activities, which are organized around the themes of data access, scientific expertise and existing coordination, aim to secure optimal use of the existing and planned data, from space and from the ground, in helio- and asteroseismology. Starting in January 1, 2013, the SpaceInn project is funded for four years by the European Union.
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Vincent Böning

Session: Poster session: Helioseismology

946 views
Date of upload:
07.09.2015
Co-author:
Markus Roth, Wolfgang Zima, Aaron C. Birch, Laurent Gizon
Abstract:
We extend an existing Born approximation model for calculating the linear sensitivity of helioseismic travel-times to flows from Cartesian to spherical geometry. This development is necessary to use the Born approximation for inferring large-scale flows in the deep solar interior. Two consistency tests show that results for our sensitivity kernels agree with reference values to within a few percent. Consequently, we evaluate the impact of different data analysis filters on the kernels for a meridional travel-distance of 42 degrees. When mainly low-degree modes are used (roughly l < 70), the sensitivity is concentrated in deeper regions and it visually best resembles a ray-path like structure, otherwise the sensitivity is concentrated near the surface. Among the different low-degree filters used, we find the phase-speed filtered kernel to be best localized at depth.
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Vincent Böning

Session: Poster session: Helioseismology

984 views
Date of upload:
07.09.2015
Co-author:
Markus Roth, Jason Jackiewicz
Abstract:
We present the current status of an undergoing validation of a recently developed model for computing spherical Born approximation sensitivity functions for flows. In a first step, power spectra and reference cross-correlations from the model and a simulation of Hartlep et al. (2013) are matched. Some difficulties in obtaining such a match are discussed. In a second step, travel times from the forward model and from the simulation, which includes a standard meridional flow profile, are to be compared. The analysis procedure including the use of phase-speed filters is identical to the one employed in Jackiewicz et al. (2015). Furthermore, we present a novel approach for a fast computation of integrated sensitivity functions which can be used for interpreting rotationally symmetric flows such as differential rotation and meridional flow.
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Vincent Böning

Session: Poster session: Helioseismology

984 views
Date of upload:
07.09.2015
Co-author:
Emmanuel Hecht, Markus Roth
Abstract:
In current approaches to time-distance helioseismology, the line-of-sight projection effect on the traveltimes is not fully taken into account. Furthermore, filtering of full-disc data induces leakage due to the projection onto the CCD, which has so far not been accounted for. We develop a theoretical approach to consider these effects when computing sensitivity functions. As the formulas obtained do not seem to give results for spherical Born approximation sensitivity functions in a reasonable computation time, we develop tests to estimate the strength of the effects.
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Hui Zhao

Session: Poster session: Helioseismology

668 views
Date of upload:
09.09.2015
Co-author:
Dean-Yi Chou(Physics Department, National Tsing Hua University, Hsinchu, Taiwan)
Abstract:
The solar acoustic waves are modified by the interaction with sunspots. The interaction can be treated as a scattering problem: an incident wave propagating toward a sunspot is scattered by the sunspot into different modes. The absorption cross section and scattering cross section are two important parameters in the scattering problem. In this study, we use the wavefunction of the scattered wave, measured with a deconvolution method, to compute the absorption cross section σab and the scattering cross section σsc for the radial order n = 0 − 5 for two sunspots, NOAAs 11084 and 11092. In the computation of the cross sections, the random noise and dissipation in the measured acoustic power are corrected. For both σab and σsc, the value of NOAA 11092 is greater than that of NOAA 11084, but their overall n dependences are similar: decreasing with n. The ratio of σabs of two sunspots is approximately equal to the ratio of sunspot radii for all ns, while the ratio of σscs of two sunspots is greater than the ratio of sunspot radii and increases with n. This suggests that σab is approximately proportional to the sunspot radius, while the change of σsc with radius is faster than the linear increase.
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Aditi Sood

Session: Poster session: Solar physics

790 views
Date of upload:
09.09.2015
Co-author:
Rainer Hollerbach, Eun-jin Kim
Abstract:
Magnetic fields and shear flows play an important role in many systems including astrophysical, geophysical and laboratory plasmas. We report how the growth of magnetic fields is modified by large-scale shear flow by investigating a kinematic dynamo in a spherical shell of highly conducting fluid surrounded by an insulator. A small scale prescribed velocity field is taken to be axisymmetric, steady and strongly helical. Small-scale flow is chosen in such a way it allows the dipole/quadrupole decoupling for magnetic field $B$. On the other hand, large-scale shear flows are taken to be in radial or latitudinal directions. By numerically solving induction equation with the prescribed small-scale flow and large-scale shear flow, we investigate the effects of large scale shear on dynamo for different azimuthal $m$ modes for large magnetic Reynolds number $R_m$ such as the growth rate and structures of magnetic field $B$. In all cases, the growth rate of the magnetic field is found to decrease as the strength of shear flow increases, which indicates that the dynamo is suppressed in the presence of shear.
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Richard Bogart

Session: Poster session: Helioseismology

758 views
Date of upload:
09.09.2015
Co-author:
Charles Baldner, Sarbani Basu
Abstract:
Although the principles involved in understanding ring-diagram mode frequencies are well understood, the procedures for determining those frequencies in the power spectra of flattened geometries are plagued by several systematic effects which are not well understood. It is possible to overcome these effects in certain cases by comparing inversions of the fitted mode parameters, or just the parameters themselves, for particular targets with those for otherwise similar targets. We can thus draw useful information about features localized in both space and time, such as regions of anomalous flows or the thermal structures of active regions. But reliable measurements of the large-scale or long-term mean dynamical structure of the near-surface regions, particularly the profiles of differential rotation and meridional circulation, may require more robust estimations of the mode parameters than are presently available. We describe the known systematic effects in the extensive ring-diagram analysis of HMI Doppler data and explore some methods of overcoming or dealing with them.
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Anne-Marie Broomhall

Session: Poster session: Helioseismology

822 views
Date of upload:
10.09.2015
Co-author:
Dmitrii Kolotkov, Valery Nakariakov
Abstract:
It is well-known that the Sun’s magnetic activity varies primarily on a time scale of 11yrs. It is also well known that the frequencies of the Sun’s natural acoustic oscillations vary in-phase with surface and atmospheric measures the Sun’s activity. Additionally, both atmospheric activity proxies and helioseimic frequencies exhibit variations on timescales much shorter than 11yrs, including the ‘quasi-biennial’ periodicity. Solar periodicities, including the 11yr cycle, are hard to characterise, as they vary in both length and amplitude. We have used empirical mode decomposition techniques to separate time variations in acoustic mode frequencies, the 10.7cm flux and sunspot areas into a set of intrinsic modes. We then use the Huang-Hilbert transform to characterise the periodicities of these intrinsic modes. The periodicities obtained are consistent between the different activity proxies, including the quasi-biennial periodicity. This indicates that the quasi-biennial behaviour observed at the solar surface and in the solar atmosphere is also symptomatic of the solar interior.
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Anne-Marie Broomhall

Session: Poster session: Solar physics

1365 views
Date of upload:
10.09.2015
Co-author:
Chloe Pugh, Valery Nakariakov
Abstract:
Quasi-periodic pulsations (QPPs) are a common feature of solar flares that are observed in many different wavelengths. Although QPPs appear not to be as abundant in white light Kepler flare light curves as they are in solar flares, albeit in different wavelengths the structure of the pulsations are strikingly similar, hinting that the same underlying processes govern both solar and stellar flares. Here we consider a special case, observed on KIC9655129, which shows evidence of multiple periodicities. We speculate that the presence of multiple periodicities is a good indication that the QPPs were caused by magnetohydrodynamic oscillations, further strengthening the case that the physical processes in operation during stellar flares are at least analogous to those in solar flares.
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mutlu yildiz

Session: Poster session: Asteroseismology

798 views
Date of upload:
10.09.2015
Co-author:
Z. ÇELİK ORHAN, C. KAYHAN and M. YILDIZ
Abstract:
Solar-like oscillation frequencies of 93 target stars of Kepler and CoRoT are analyzed. In the present study, we present results for two of them. Recently, two new reference frequencies nu_min1 and nu_min2 are found in the spacing of solar-like oscillation frequencies of stellar interior models. In order to fit model frequencies to observational frequencies, we change model mass and hydrogen abundance. We also try to obtain similar patterns around min1 and min2 for model and observational frequencies.
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Kyeongsoo Hong

Session: Session I: Solar and stellar observations

611 views
Date of upload:
20.07.2016
Co-author:
Jae Woo Lee, Jae-Rim Koo
Abstract:
We present high resolution spectra of the eclipsing binary AB Cas with a δ Sct-type pulsating star, which were obtained using the Bohyunsan Optical Echelle Spectrograph in Korea. The radial velocities (RVs) for the primary and secondary components are measured from a total of 27 spectra, secured during 2 nights on October 2015. In order to obtain the accurate physical properties, we simultaneously analyzed our RV curves together with previously published uvby light-curves. Individual masses, radii, and effective temperatures of both components are determined to be M1=2.01±0.02 Msun, M2=0.37±0.02 Msun, R1=1.84±0.02 Rsun, and R2=1.69±0.03 Rsun, Teff,1=8,000±250 K and Teff,2=4,900±150 K, respectively. In addition, we investigate the evolutionary history of AB Cas using theoretical evolutionary models to give the best representation for their physical parameters. All of these indicates that AB Cas is an oscillating Algol-type eclipsing binary (oEA) with the less massive and cool secondary star filling its inner Roche lobe, which may have experienced rapid mass transfer.
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Pere L. Pallé

Session: Session I: Solar and stellar observations

1333 views
Date of upload:
03.08.2016
Co-author:
Abstract:
One of the outstanding and unforeseen results from the Kepler mission is our new insight and understanding of red giant stars. These highly evolved stars, which are in the last stages of their life, provide extremely useful information when trying to develop stellar evolutionary models. Furthermore, they show stochastically excited oscillations thus allowing to use asteroseismic techniques to derive conditions of the most internal layers. Bright giants stars are well suited to be studied with the 1m telescopes in the Stellar Observations Network Group project (SONG) using a high resolution echelle spectrograph performing high precision measurements of their the radial velocity. The prototype node- the Hertzsprung SONG telescope- was inaugurated in October 2014 and is located at the Teide Observatory on Tenerife and providing continuous and high quality observations since then, When selecting the best targets for SONG, a precision of 1-2 m/s per point is reachable using the iodine method and a number of red giants have been observed with the SONG telescope since scientific operation started. In this talk we present the first results of these specific campaigns for a few red giants in which eigenmodes have been identified and their global seismic parameters derived.
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Dean-Yi Chou

Session: Session III: Solar and stellar seismology

811 views
Date of upload:
08.09.2015
Co-author:
Abstract:
See the file.
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Dean-Yi Chou

Session: Session III: Solar and stellar seismology

1074 views
Date of upload:
08.09.2015
Co-author:
Abstract:
See the file.
First Name Last Name Affiliation