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Seismology of the Sun and the Distant Stars 2016 Free Conference is closed

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spacetk16

Hosted by Markus Roth

Affiliation Thüringer Landessternwarte Tautenburg

Angra do Heroísmo, Terceira-Açores, Portugal

10.07.2016 - 14.07.2016

Organizing institutions

INSTITUTO DE ASTROFÍSICA E CIÊNCIAS DO ESPAÇO, PORTO, PORTUGAL

Insitute for Astrophysics and Space Sciences, Porto, Portugal

Main category Natural Sciences (Astrophysics and Astrononmy)

Conference/Workshop objectives

For the last 30 years, since the meeting on Seismology of the Sun and the Distant Stars held in Cambridge, in 1985, the range of seismic data and associated science results obtained has far exceeded the expectations of the community. The continuous observation of the Sun has secured major advances in the understanding of the physics of the stellar interiors and has allowed us to build and prepare the tools to look at other stars. Several ground facilities and space missions have completed the picture by adding the necessary data to study stars across the HR diagram with a level of detail that was in no way foreseen in 1985.

In spite of the great science successes, astero- and helioseismic data still contain many secrets waiting to be uncovered. The opportunity to use the existing data and tools to clarify major questions of stellar physics (mixing, rotation, convection, and magnetic activity are just a few examples) still needs to be further explored. The combination of data from different instruments and for different targets also holds the promise that further advances are indeed imminent. At the same time we also need to prepare the future, as major space missions and ground facilities are being built in order to collect more and better data to expand and consolidate the detailed seismic view of the stellar population in our galaxy.

This conference aims at reviewing the major science achievements resulting from the extensive data collections available from space missions and ground facilities, as well as the tools the community has developed to study and explore those data. This will also include planning the asteroseismic activities of the TESS mission in preparation for its launch next year. The present view is fundamental to prepare the forthcoming facilities that will provide the data necessary to address challenging questions that have not yet been answered with the current data. The optimal way to achieve that should be one of the major outcomes of the conference which is expected to set a critical milestone for the astero- and helioseismology community to prepare the future.

The meeting will also cover major synergies with related fields, which benefit from a deeper understanding of the structure and evolution of the sun and stars across the HR diagram. These include topics covering the characterization of planet hosts, and their exoplanets, the description of stellar populations and impact on Galactic evolution, as well as star and planet formation and the early evolution of planetary systems. Also of major relevance is the driving of space weather in the solar system and other stellar systems and its impact on habitability, linking stellar evolution to the search for life.

Further information is available at: http://www.iastro.pt/research/conferences/spacetk16/

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Local organizing committee

Margarida S. Cunha (Co-Chair)
João M. T. S. Ferreira (Co-Chair)
Paulo Peixoto
Elsa Silva

Scientific organizing committee (SOC)

Conny Aerts (Belgium)
Sarbani Basu (United States of America)
Timothy Bedding (Australia)
William Chaplin (United Kingdom)
Jørgen Christensen-Dalsgaard (Denmark, Co-Chair)
Margarida S. Cunha (Portugal)
João Miguel T.S. Ferreira (Portugal)
Rafael García (France)
Laurent Gizon (Germany)
Hans Kjeldsen (Denmark)
David W. Latham (United States of America)
Eric Michel (France)
Mário J.P.F.G. Monteiro (Portugal, Co-Chair)
Pere L. Pallé (Spain)
Ennio Poretti (Italy)
Markus Roth (Germany)

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Sessions

S1. Opening Session
S2. Space Missions & Data
S3. Special Session: TASC & KASC
S4. Special Session: SpaceInn & HELAS
S5a. Poster Session I
S5b. Poster Session II
S6. Physics: Convection and Mode Behaviour
S7. Physics: Rotation
S8. Physics: Magnetic Field and Activity
S9. Seismology: Stars Near and in the Main Sequence
S10. Seismology: Stars Beyound the Main Sequence
S11. Synergies: Stellar Evolution and Galactic Populations
S12. Synergies: Binaries
S13. Synergies: Planets
S14. Closing Session

Programme

Invited speakers

Laurent Eyer (University of Geneva, CH)

Gerald Handler (Nicolaus Copernicus Astronomical Center, PL)

Yvonne Elsworth (University of Birmingham, UK)

Marie-Jo Goupil (Observatoire de Paris, FR)

Bjoern Loeptien (University of Goettingen, DE)

Dave Latham (Harvard-Smithsonian Center for Astrophysics, USA)

Tiago Campante (University of Birmingham, UK)

Rafael Garcia (CEA Saclay, FR)

Warwick Ball (Institut für Astrophysik Göttingen, DE)

Jan Langfellner (Max-Planck-Institut für Sonnensystemforschung, DE)

Tamara Rogers (Newcastle University, UK)

Rhita-Maria Ouazzani (Aarhus University, DK)

Anne-Marie Broomhall (University of Warwick, UK)

Kyle Augustson (CEA Saclay, FR)

Dennis Stello (University of Sydney, AU)

Vichi Antoci (Aarhus University, DK)

Konstanze Zwintz (University of Innsbruck, AT)

Jan-Torge Schindler (University of Arizona, US)

Santi Cassisi (INAF - Osservatorio Astronomico di Teramo, IT)

Kevin Belkacem (Observatoire de Paris, FR)

Sebastien Deheuvels (Institut de Recherche en Astrophysique et Planétologie, FR)

Andrea Miglio (University of Birmingham, UK)

Cristina Chiappini (Leibniz-Institut fuer Astrophysik Potsdam, DE)

Andrew Tkachenko (KU Leuven, BE)

Andrej Prsa (Villanova University, USA)

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Important dates

3 April 2016: Abstract submission for oral contributions and grant application (new date).
24 April 2016: Early registration closes (new date).
1 June 2016*: Late registration and abstract submission for posters closes.

Registration and payment information

For registration visit:
http://www.iastro.pt/research/conferences/spacetk16/registration.html

Conference venue Angra do Heroísmo, Terceira-Açores, Portugal

Hotel information

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There are no uploaded videos yet.

Markus Roth

Session: S1. Opening Session

1256 views

Date of upload:

11.07.2016

Co-author:

SpaceInn Board

Abstract:

The collaborative project "SpaceInn - Exploitation of Space Data for Innovative Helio- and Asteroseismolgy" is funded under the European Union’s Seventh Framework Programme from January 2013 – December 2016. The European Helio- and Asteroseismology Network (HELAS) has initiated this project with the mission to build on the existing European strength in the field of time-domain stellar physics. In the last three years SpaceInn activities aimed to secure optimal use of the existing and planned data, from space and from the ground, in helio- and asteroseismology in order to improve access and scientific exploitation of the existing data. The main goals of the project include: -Establish coordinated archives of space- and ground-based data, as well as of the results of the analyses of these data. This includes tools for efficient data access. -Secured long-term preservation of these, often unique, data. -Coordinated utilization of the data, resulting in a much improved understanding of solar structure, dynamics and activity, as well as of stellar structure and evolution -An increased awareness of the field, amongst the general public and at all levels of the educational system, throughout Europe. In this talk I will present all these activities and the main outcome of the project.

Vincent Prat

Session: S7. Physics: Rotation

1266 views

Date of upload:

14.07.2016

Co-author:

Stéphane Mathis, François Lignières, Jérôme Ballot, Pierre-Marie Culpin

Abstract:

Most of the information we have about the internal rotation of stars comes from modes that are weakly affected by rotation, for instance thanks to rotational splittings. In contrast, we present here a method (based on the asymptotic theory of Prat et al. 2016, A&A, 587, A110) which allows us to analyze the signature of rotation where its effect is the most important, that is in low-frequency modes that are strongly affected by rotation.

Tiago Campante

Session: S3. Special Session: TASC & KASC

1087 views

Date of upload:

14.07.2016

Co-author:

Abstract:

New insights on stellar evolution and stellar interiors physics are being made possible by asteroseismology. Throughout the course of the Kepler mission, asteroseismology has also played an important role in the characterization of exoplanet-host stars and their planetary systems. The upcoming NASA's Transiting Exoplanet Survey Satellite (TESS) will be performing a wide-field survey for planets that transit bright nearby stars. In addition, its excellent photometric precision, combined with its fine time sampling and long intervals of uninterrupted observations, will enable asteroseismology of solar-type and red-giant stars. We developed a simple test to estimate the detectability of solar-like oscillations in TESS photometry of any given star. Based on an all-sky stellar and planetary synthetic population, we go on to predict the asteroseismic yield of the TESS mission, placing emphasis on the yield of exoplanet-host stars for which we expect to detect solar-like oscillations. This is done for both the cohort of target stars (observed at a 2-min cadence) and the cohort of full-frame-image stars (observed at a 30-min cadence). A similar exercise is also conducted based on a compilation of known host stars. With several tens of TESS target hosts (mainly F dwarfs and subgiant stars) and up to 200 full-frame-image hosts (at the low-luminosity end of the red-giant branch) for which asteroseismology will become possible, not to mention the over 100 known host stars, this equates to a threefold improvement in the asteroseismic yield of exoplanet-host stars when compared to Kepler's.

Joergen Christensen-Dalsgaard

Session: S2. Space Missions & Data

1140 views

Date of upload:

15.07.2016

Co-author:

Abstract:

The SONG Hertzsprung telescope, at the Observatorio del Teide, Izana, Tenerife, is a prototype for the telescopes in the planned SONG (Stellar Observations Network Group) network for asteroseismology and exoplanet studies. It has an aperture of 1 m and is equipped with a high-resolution spectrograph, with an iodine reference, and a two-channel lucky-imaging camera. Operations are fully robotic. The telescope entered operation in the Spring of 2014 and, as one of the first extended observing programmes, has observed the V = 3.42 subgiant μ Herculis (HD 161797) for a total of 200 nights in 2014 and 2015. This has yielded excellent data on the oscillation frequencies, with a clear indication of mixed modes, and other oscillation properties. I present these observations, demonstrating the excellent quality of the telescope and instrumentation, and discuss the first inferences from the analysis of the results.

Aline Vidotto

Session: S13. Synergies: Planets

1196 views

Date of upload:

16.07.2016

Co-author:

Abstract:

In this talk, I review the latest results on surveys of stellar magnetism and present evidence and suggestions that planets could affect the magnetic activity of their host stars.

Zhi-Chao Liang

Session: S4. Special Session: SpaceInn & HELAS

1165 views

Date of upload:

18.07.2016

Co-author:

Thomas L. Duvall Jr., Laurent Gizon

Abstract:

In this study, we apply time-distance helioseismology to the medium-degree Dopplergrams observed by SOHO/MDI and SDO/HMI, in order to measure meridional circulation in the deep convection zone. The results are averaged over the same observation period (May 2010 to Apr 2011) of the two data set and then compared with each other. After the removal of the known center-to-limb variation and a roll-angle uncertainty in MDI data by registering with HMI data, the travel-time results obtained from MDI and HMI data are consistent. Even the fluctuations in the travel-time differences match closely. Furthermore, we analyse 4-year HMI data and exclude the active regions from our analysis. The travel-time measurements of the meridional flow using the HMI data show a time variation in the convection zone similar to that using MDI data measured by Liang & Chou (2015).

Warrick Ball

Session: S6. Physics: Convection and Mode Behaviour

1080 views

Date of upload:

19.07.2016

Co-author:

Abstract:

Inaccurate modelling of the near-surface layers of solar models causes a systematic difference between modelled and observed solar mode frequencies. This difference—known as the “surface effect” or “surface term”—presumably also exists in other solar-like oscillators and must somehow be corrected to accurately relate mode frequencies to stellar model parameters. After briefly describing the various potential causes of surface effects, I will review recent progress along two different lines. First, various methods have been proposed for removing the surface effect from the mode frequencies and thereby fitting stellar models without the disproportionate influence of the inaccurate near-surface layers. Second, three-dimensional radiation hydrodynamics simulations are now being used to replace the near-surface layers of stellar models across a range of spectral types, leading to predictions of how some components of the surface effect vary between stars. Finally, I shall briefly discuss the future of the problem in terms of both modelling and observation.

Antonio García Hernández

Session: S9. Seismology: Stars Near and in the Main Sequence

1224 views

Date of upload:

19.07.2016

Co-author:

M. J. P. F. G. Monteiro, S. Martín, Z. Guo, D. R. Reese, J. C. Suárez, J. Pascual-Granado, A. Moya, R. Garrido

Abstract:

In the work we present here, we empirically demonstrate that a simple relation exists between a periodic pattern present in the frequency spectra of Delta Scuti stars and their mean density. This relation is homologous to that of solar-type stars. But the most important result is that this relation is indeed independent of the rotational velocity, becoming an ideal tool to constrain the pyhisical parameters of the star, even at high rotation rates. Moreover, we pushed the data one step further. Using also an estimation of the luminosity of each object, we demonstrate that it is possible, once the periodic pattern is determined, to derived the surface gravity of the star. The typical uncertainty we found for this quantity is the same as with high resolution spectroscopic data. This result might settle the degeneracy problem of the surface gravity determination with the spectra of A-type stars.

Daniel Reese

Session: S7. Physics: Rotation

1200 views

Date of upload:

21.07.2016

Co-author:

M.-A. Dupret, M. Rieutord

Abstract:

One of the greatest challenges in interpreting the pulsations of rapidly rotating stars is mode identification, i.e. correctly matching theoretical modes to observed pulsation frequencies. Indeed, the latest observations as well as current theoretical results show the complexity of pulsation spectra in such stars, and the lack of easily recognisable patterns. In the present contribution, I will describe the latest results on non-adiabatic effects in such pulsations, and show how these come into play when identifying modes. These calculations fully take into account the effects of rapid rotation, including centrifugal distortion, and are based on models from the ESTER project, currently the only rapidly rotating models in which thermal equilibrium, a prerequisite for calculating non-adiabatic effects, is achieved. Non-adiabatic effects determine which modes are excited and play a key role in the near-surface pulsation-induced temperature variations which intervene in multi-colour amplitude ratios and phase differences, as well as line profile variations.

Anne-Marie Broomhall

Session: S8. Physics: Magnetic Field and Activity

1184 views

Date of upload:

21.07.2016

Co-author:

Anne-Marie Broomhall

Abstract:

The Sun’s magnetic activity cycle varies primarily on a time scale of 11yrs from minimum to maximum and back again. It is well-known that the properties of the Sun’s acoustic oscillations are affected by the near-surface internal magnetic field: Frequencies, damping rates, and powers are all known to vary systematically with solar cycle. Careful observation of these variations, therefore, allows aspects of the Sun’s internal magnetic field to be inferred. However, the Sun is just one star and with the advent of CoROT and Kepler, oscillations can now be observed for thousands of other stars. However, despite many stars showing signs of magnetic activity in their lightcurves, to date, activity cycle-like variations in the properties of asteroseimic oscillations are sparse. I will discuss recent observations of solar cycle associated variations in helioseismic oscillation parameters, demonstrating connections with other stars and implications for our understanding of solar and stellar magnetic fields. I will finish with a discussion on how seismology can provide insights into a star’s magnetic field, without necessarily observing activity cycle-like behaviour.

Sebastien Deheuvels

Session: S10. Seismology: Stars Beyound the Main Sequence

1092 views

Date of upload:

06.09.2016

Co-author:

Abstract:

Since the detection of non-radial oscillations in over 10,000 red giants by space missions CoRoT and Kepler, the seismology of these objects has rightfully gained interest among the stellar physics community. The detection of mixed gravity-pressure modes has indeed made it possible to peer into the cores of red giants. This is currently bringing stringent constraints on several physical processes in stellar interiors that remain poorly understood but play a central role in stellar evolution, such as the nature and efficiency of mixing beyond boundaries of convective regions, or the way angular momentum is transported inside stars. We here give an overview of what the seismology of red giants has already taught us about such processes, and highlight the potential of dipole mixed modes in red giants for new advances in stellar physics.

Michel Rieutord

Session: S8. Physics: Magnetic Field and Activity

1078 views

Date of upload:

06.09.2016

Co-author:

Abstract:

The spectrum of gravito-acoustic modes is depleted in dipolar modes for a significant fraction of the giant stars observed by Kepler, a feature that can be explained by the presence of magnetic fields in the core of these stars (Fuller et al. 2015, Cantiello et al. 2016). We further investigate this scenario by considering first the oscillation spectrum of the core of a giant star modeled by a stably stratified, self-gravitating fluid sphere pervaded by a uniform and/or toroidal magnetic field. First results show a great sensitivity of the g-mode spectrum to the strength of the magnetic field. This result leads us to further investigate the possibility of using the observed spectra to determine the dissipative properties of the core and the strength of the magnetic field when modeled by a simple large-scale distribution (i.e. uniform and/or toroidal). Results of these investigations will be presented.

Daniel Holdsworth

Session: S9. Seismology: Stars Near and in the Main Sequence

1166 views

Date of upload:

08.09.2016

Co-author:

D.W. Kurtz, B. Smalley, H. Saio, G. Handler, S.J. Murphy, H. Lehmann

Abstract:

We present an analysis of the rst K2 observations of a rapidly oscillating Ap (roAp) star, HD 24355. The star was discovered to be a roAp star by Holdsworth et al. (2014), with a frequency of 224.31 c/d (2596.18 microHz; P = 6.4 min) and an amplitude of 1.51 mmag in SuperWASP broadband photometry. Spectroscopic analysis of low-resolution spectra show the star to be an A5 Vp SrEu star. The high precision K2 data allow us to identify 13 rotationally split sidelobes to the main pulsation frequency. This is the largest number of sidelobes seen in a roAp star to date. We also see an unusual pulsational phase variation as the star rotates, showing this star to be the most distorted quadrupole roAp pulsator yet observed. Modelling of this star confirms its quadrupole nature, and allows us to constrain the magnetic field strength, angle of inclination and the angle of obliquity. This is currently the only roAp star observed with the Kepler satellite in Short Cadence mode that has a photo- metric amplitude detectable from the ground, thus allowing comparison between the mmag amplitude ground-based targets and the micromag spaced-based discoveries.

May Gade Pedersen

Session: S8. Physics: Magnetic Field and Activity

1331 views

Date of upload:

08.09.2016

Co-author:

Victoria Antoci (SAC, Aarhus University) and Heidi Korhonen (Dark Cosmology Centre, University of Copenhagen)

Abstract:

Recent studies show evidence of flare-like features in 33 Kepler A-type stars which were interpreted to be intrinsic, contradicting theory. Flares in late-type stars are generated through the reconnection of magnetic field lines in stellar atmospheres. For magnetic fields to be sufficiently strong to emerge at the surface and form flares a dynamo is required, which is operated by a convective envelope. A-type stars only have shallow convective envelopes of the order of 1.3% of the total stellar radius and therefore are not expected to support flaring. On the other hand X-ray flares have been observed in strongly magnetic A- and B- type stars and through colliding winds in massive binary systems. Strong stellar winds vanish for late B-type stars and normal A-type stars only have weak global magnetic fields. Therefore, neither reconnection or strong stellar winds should support flaring in A-type stars. We analyse the 33 A-type stars previously found to be flaring, setting specific criteria in order to identify these flares. Our results strongly disagree with the numbers found in literature. However, the positive detections follow the expected correlation between flare duration and intensity. We present results on our investigation of the origin of these flares, considering effects from contamination and combined light as well as study binarity from spectroscopy and possible circumstellar disks.

Jakob Mosumgaard

Session: S9. Seismology: Stars Near and in the Main Sequence

1122 views

Date of upload:

13.10.2016

Co-author:

Abstract:

Brief presentation on the procedure for implementing T-tau relations extracted from 3D simulations into 1D stellar models. More specifically, how the T-tau relations from Trampedach et al. (2014, MNRAS, 442, 805) and variable mixing-length parameter from Trampedach et al. (2014, MNRAS, 445, 4366) have been implemented in the Garching Stellar Evolution Code (GARSTEC, see Weiss & Schlattl, 2008, Astrophys. Space Sci., 316, 99).

Gaël Buldgen

Session: S9. Seismology: Stars Near and in the Main Sequence

1115 views

Date of upload:

21.10.2016

Co-author:

Daniel Reese, Marc-Antoine Dupret

Abstract:

In the past few years, the CoRoT and Kepler missions have carried out what is now called the space photometry revolution. This revolution is still ongoing thanks to K2 and will be continued by the Tess and Plato2.0 missions. However, the photometry revolution must also be followed by progress in stellar modelling, in order to lead to more precise and accurate determinations of fundamental stellar parameters such as masses, radii and ages. In this context, the long-lasting problems related to mixing processes in stellar interior is the main obstacle to further improvements of stellar modelling. In this talk, we will apply structural asteroseismic inversion techniques to targets from the Kepler LEGACY sample and analyse how these can help us constrain the fundamental parameters and mixing processes in these stars. Our approach is based on previous studies using the SOLA inversion technique (Pijpers & Thompson 1994) to determine integrated quantities such as the mean density (Reese et al. 2012), the acoustic radius, and core conditions indicators (Buldgen et al. 2015a, Buldgen et al. 2015b), and has already been successfully applied to the 16Cyg binary system (Buldgen et al. 2016, Buldgen et al. in prep). We will show how this technique can be applied to the Kepler LEGACY sample and how new indicators can help us to further constrain the chemical composition profiles of stars as well as provide stringent constraints on stellar ages.

René Kiefer

Session: S8. Physics: Magnetic Field and Activity

1807 views

Date of upload:

27.02.2017

Co-author:

Ariane Schad, Guy Davies, Markus Roth

Abstract:

Context. The Sun and solar-like stars undergo activity cycles for which the underlying mechanisms are not well understood. The oscillations of the Sun are known to vary with activity cycle and these changes provide diagnostics on the conditions below the photosphere. Kepler has detected oscillations in hundreds of solar-like stars but as of yet, no widespread detection of signatures of magnetic activity cycles in the oscillation parameters of these stars have been reported. Aims. We analyse the photometric short cadence Kepler time series of a set of 24 solar-like stars, which were observed for at least 960 days each, with the aim to find signatures of stellar magnetic activity in the oscillation parameters. Methods. We analyse the temporal evolution of oscillation parameters by measuring mode frequency shifts and changes in the height of the p-mode envelope. Results. For 22 of the 24 investigated stars, we find significant frequency shifts in time, indicating stellar magnetic activity. For the most prominent example, KIC 8006161, we find that, similar to the solar case, frequency shifts are smallest for the lowest and largest for the highest p-mode frequencies. Conclusions. These findings show that magnetic activity can be routinely observed in the oscillation parameters for solar-like stars. The large proportion of stars for which this is the case opens up the possibility to place the Sun and its activity cycle in the context of other stars.

Vincent Böning

Session: S5a. Poster Session I

1342 views

Date of upload:

12.07.2016

Co-author:

Markus Roth, Jason Jackiewicz, Shukur Kholikov

Abstract:

Accurate meridional flow measurements are important for understanding the solar dynamo. Recent in- versions for meridional flows have not yet reached a consensus on the nature of the meridional flow in depths greater than about 0.9 solar radii. In time-distance helioseismology, current modelling of the solar interior for meridional flow inversions is performed using ray kernels, which assume that waves propagate along infinitely thin ray paths. The Born approximation may constitute a more accurate approach as it models the first order perturbation to the wave field in the whole solar interior. We present the current status of an undergoing validation of a recently developed model for computing spherical Born approxi- mation sensitivity functions suitable for inferring meridional flows. In addition, we compare Born and ray approximations using flow models.

Emanuele Papini

Session: S5a. Poster Session I

1491 views

Date of upload:

13.07.2016

Co-author:

Laurent Gizon

Abstract:

Stellar acoustic oscillations are affected by magnetic activity, however it is unclear how a single starspot would affect the power spectrum of oscillations. Since the starspot rotates with the star, it causes a perturbation that is unsteady in the observer’s frame. Each (n, l) multiplet appears as (2l + 1) 2 blended peaks in the power spectrum, whose amplitudes depend on the star’s inclination and on the latitude of the starspot. We simulate example power spectra using both perturbation theory and numerical simulations.

Masao Takata

Session: S5a. Poster Session I

1384 views

Date of upload:

14.07.2016

Co-author:

Abstract:

The frequency condition for the mixed modes of nonradial stellar oscillations is generally examined by a simple physical model based on a running-wave picture. The coupling coefficient between the gravity-wave oscillation in the core and the acoustic-wave oscillation in the envelope is expressed in terms of the reflection coefficient at the intermediate evanescent region. It is also argued that the eigenmode condition should appropriately be modified if the wave generated near the surface and transmitted to the core is (partially) lost either by damping or scattering in the core. The derived formulae should be helpful in understanding the physics of the mixed modes in general, the origin of the red giants with depressed dipolar modes, and the effect of radiative damping in the core of the red giant stars.

Jérôme Ballot

Session: S5b. Poster Session II

1470 views

Date of upload:

14.07.2016

Co-author:

M. Aurière, S. Deheuvels, R. A. García, F. Lignières, S. Mathur, P. Petit

Abstract:

Spectropolarimetric measurements allow us to detect and measure magnetic field through Zeeman effect in stellar photospheres. We observed with the spectropolarimeters Narval (at Telescope Bernard Lyot) and ESPADONS (at CFHT) a few Kepler Red Giants in 2012 and 2013, especially four stars showing depressed dipolar modes. Interestingly, recent seismic studies by Fuller et al. (2015) suggest these stars had a magnetic history. After presenting shortly the technique, I will detail the detections we did and the constraints we put in surface magnetic fields, then I will discuss the origin of these fields by comparing these observations to a broader sample of red giants observed by Aurière et al. (2015).

Chris Hanson

Session: S5a. Poster Session I

1682 views

Date of upload:

14.07.2016

Co-author:

Michael Leguèbe, Damien Fournier, Aaron C. Birch, Laurent Gizon in Collaboration with Inria team Magique3D

Abstract:

Forward problems in local helioseismology have thus far been addressed in a semi-analytical fashion using the Born approximation and normal-mode expansions or direct simulations. However, it has proven difficult to take into account geometrical and instrumental effects. To avoid these difficulties we employ a numerical method to determine the impulse response of a solar model in a 2.5D geometry. Solving the wave equation in the frequency domain avoids the difficulties (instabilities) faced in the time domain. This framework is flexible, computationally efficient, and produces solar-like power spectrum and cross-covariance that agree reasonably with observations, including the high-frequency continuous spectrum. Additionally, we present accurate travel-time sensitivity kernels for perturbations to the solar medium which hint at the promising potential of this framework in future forward and inversion problems.

Chris Hanson

Session: S5a. Poster Session I

5776 views

Date of upload:

14.07.2016

Co-author:

Michael Leguèbe, Damien Fournier, Aaron C. Birch, Laurent Gizon in Collaboration with Inria team Magique3D

Abstract:

We compute acoustic Green’s functions in an axisymmetric solar background model, which may include a meridional flow and differential rotation. The wave equation is solved in the frequency domain using a finite element solver. A transparent boundary condition for the waves is implemented in the chromosphere, which represents a great improvement in computational efficiency compared to implementations based on ’sponge layers’. We perform various convergence studies that demonstrate that wave travel times can be computed with an accuracy of 0.001 s. This high level of numerical accuracy is required to interpret travel times in the deep interior, and is achieved thanks to a refined mesh in the near surface layers and around the source of excitation. The wave solver presented here lays the ground for future iterative inversion methods for flows in the deep solar interior.

Charles Kuehn

Session: S5b. Poster Session II

1294 views

Date of upload:

14.07.2016

Co-author:

Pawel Moskalik, Jason Drury

Abstract:

Observations by Kepler/K2 have revolutionized the study of RR Lyrae stars by allowing the detection of new phenomena, such as low amplitude additional modes and period doubling, which had not previously been seen from the ground. During campaign 2, K2 observed the globular cluster M4, providing the first opportunity to study a sizeable group of RR Lyrae stars that belong to a single population; the other RR Lyrae stars that have been observed from space are field stars in the galactic halo and thus belong to an assortment of populations. In this poster we present the results of our study of the RR Lyrae variables in M4 from K2 photometry. We have identified additional, low amplitude pulsation modes in both observed RRc stars. In 3 RRab stars we have found the Blazhko effect with periods of 16.6d, 22.4d and 44.5d.

ehsan moravveji

Session: S5a. Poster Session I

1426 views

Date of upload:

14.07.2016

Co-author:

R. H. D. Townsend, C. Aerts & S. Mathis

Abstract:

KIC 7760680 was discovered by Papics et al. (2015) to be the richest known Slowly Pulsating B star, by exhibiting 36 consecutive dipole prograde (l=1, m=+1) gravity (g-) modes. Moreover, the monotonically decreasing period spacing of the series, in addition to the local dips in the pattern confirm that this star is a moderate rotator, with clear mode trapping in chemically inhomogeneous layers. This star, thus, constitutes a great laboratory to probe mixing and transport processes in pulsating rotating massive stars. We compute a dense MESA (Paxton et al. 2011, 2013, 2015) grid of evolutionary tracks by varying initial mass, metallicity, overshooting and diffusive non-standard mixing in the radiative envelope. We employ GYRE (Townsend & Teitler 2013) to compute high-order dipole prograde g-mode frequencies using the traditional approximation of rotation to incorporate the effects of the Coriolis acceleration on g-mode frequencies. This detailed forward asteroseismic modelling reveals that KIC 7760680 is a moderately rotating B star with a mass ~3.25 Msun. By simultaneously matching the slope of the period spacing, and the number of modes in the observed frequency range, we deduce that the equatorial rotation frequency of KIC 7760680 is 0.4805 1/day, which is 26% of its Roche break up frequency. The relative deviation of the model frequencies and those observed is less than one percent. We succeed to tightly constrain the convective core overshooting. We demonstrate that an exponentially-decaying model with its parameter fov=0.024 ± 0.001 allows a better agreement than those with a classical step-function overshoot. This also means that convective core overshooting can coexist with moderate rotation. Finally, we constrain the best value for diffusive non-standard mixing in the radiative stable envelope to be confined to log D_ext=0.75 ± 0.25, where D_ext (in cm^2/sec is the effective diffusivity. This is three to ten orders of magnitude smaller than the current theoretical predictions. This can be the signature of a weak differential rotation and of an efficient transport of angular momentum in the vertical direction.

Laura Ketzer

Session: S5b. Poster Session II

1342 views

Date of upload:

14.07.2016

Co-author:

A.S. Baran, M.D. Reed, R.H.Østensen, J.H. Telting, C.S. Jeffery, P. Németh

Abstract:

We present an analysis of the pulsating subdwarf B (sdB) star EPIC 203948264, observed during Campaign 2 of the extended Kepler mission. A time series analysis of the short cadence data set has revealed a rich g-mode pulsation spectrum with 20 independent pulsation periods between 0.5 and 2.8 hours. Most of the pulsations fit the asymptotic period sequences for ℓ = 1 or 2, with average period spacings of 261.34+/-0.78 and 151.18+/-0.34 s, respectively. The pulsation amplitudes are below 0.77 ppt and vary over time. Radial velocity measurements give no indication for binarity in this star. We did not find any clear rotationally induced pulsation multiplets, which indicates that the rotation period of the star is longer than about 46 days. By characterizing the various pulsation modes, we can constrain structural models of sdB stars. This is a promising approach to enhancing our understanding of horizontal branch stars.

Charlotte Gehan

Session: S5b. Poster Session II

1311 views

Date of upload:

14.07.2016

Co-author:

Beoît Mosser, Eric Michel

Abstract:

Red giant stars have proved to be asteroseismic targets of choice: conditions in their interior are met to couple pressure waves propagating in the envelope and gravity waves propagating in the core, so that we have a direct view on their core through mixed modes, which is not the case for main-sequence stars. In particular, asteroseismology of red giants gives us the opportunity to study their internal rotation, especially their core rotation. Rotation is known to deeply impact the evolution of stars, but including rotation in stellar evolution models is still challenging. Models predict central rotation rates at least ten times too large compared to asteroseismic measurements. This implies that angular momentum transport is at work in stellar interiors, whose physical mechanisms are not yet fully understood. It is thus of prime importance to know how internal rotation evolves in time. This is particularly true for red giants, in order to better characterise the physical processes operating in the deepest region of these stars. Such a study requires core rotation measurements for a maximum number of red giants. In this context, I have developed an automatic method to determine the mean core rotation of red giant stars presenting different evolutionary stages with Kepler data. In the future, obtaining mean core rotation rates for thousands of red giants will improve the characterisation of the physical mechanisms causing angular momentum transport in these stars, and therefore our understanding of stellar evolution. I will present preliminary results that I obtained with a new and promising method to determine automatically core rotation rates of red giants. Such an automated measurement of the core rotation of red giants will moreover be required to analyse the hundreds of thousands of oscillation spectra that PLATO should provide in a few years. Hence this automated method is paving the way for the future PLATO data.

Isabel Colman

Session: S5b. Poster Session II

1312 views

Date of upload:

14.07.2016

Co-author:

Daniel Huber, Tim Bedding

Abstract:

We present an analysis of 93 oscillating red giants from NASA's Kepler mission which exhibit anomalous single-frequency peaks in their amplitude spectra. These peaks may be indicative of binary star systems, with frequencies such that the companion star's orbit would be within the red giant's convective envelope. Alternatively, the observed phenomenon may be due to a close binary orbiting a red giant in a triple system, or binary systems contaminating the pixels around the target star. We eliminate 46 stars in the sample as blends. However, we find that in 47 cases the anomalous peaks are indistinguishable from the target star to within a resolution of 4", the size of a Kepler pixel. This suggests that we are either observing contamination by a line-of-sight background or foreground binary system, or a physical association. We examine a Galaxia model of the Kepler field of view to estimate background star counts and find that it is highly unlikely that all targets can be explained by chance alignments. From this, we conclude that these stars may comprise a population of physically associated systems.

Earl Bellinger

Session: S5b. Poster Session II

1488 views

Date of upload:

15.07.2016

Co-author:

George C. Angelou, Saskia Hekker, Sarbani Basu, Warrick Ball, Elisabeth Guggenberger

Abstract:

We use machine learning to build a constrained multiple regression model for rapidly estimating the fundamental stellar parameters of main-sequence solar-like stars (Bellinger & Angelou 2016). We train a random forest of decision trees with scikit-learn on a matrix of stellar models generated with MESA that we varied quasi-randomly in mass, initial helium and metallicity abundances, mixing length, the strength of convective overshooting, and the efficiency of gravitational settling. We additionally compute frequencies of each stellar model using ADIPLS and summarize them to obtain averaged large and small frequency separations and frequency ratios. We supply the global asteroseismic properties and other observable quantities of our stellar models to the random forest algorithm and produce a statistical model relating observable quantities to fundamental stellar parameters. We validate this technique on a hare-and-hound exercise and the Sun, and then apply it to 16 Cyg A & B and finally 34 planet-hosting candidates.

Markus Roth

Session: S5a. Poster Session I

1852 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.

László Molnár

Session: S5b. Poster Session II

1481 views

Date of upload:

15.07.2016

Co-author:

Emese Plachy, Péter Klagyivik, Áron L. Juhász, Róbert Szabó, Zachary Dalessandro, Benjamin Kratz, Justin Ortega, Shashi Kanbur

Abstract:

Space-based photometric missions revealed a surprising abundance of millimagnitude-level additional modes in RR Lyrae stars. The modes that appear in the modulated fundamental-mode (RRab) stars can be ordered into four major categories. Period doubling, caused by the resonant ninth overtone, and the mode at ~0.6 P0 that may potentially correspond to the second overtone, are relatively abundant in these stars. In more rare cases (including RR Lyr itself), the additional modes can be identified with the first overtone, and finally some fall outside the above mentioned categories, so they are most likely non-radial modes. Here we present a census of the additional modes based on the K2 Two Wheel Engineering Test run and Campaigns 0-3 and 6 of the K2 mission, the largest sample obtained with space-based photometry so far.

Othman Benomar

Session: S5b. Poster Session II

1402 views

Date of upload:

15.07.2016

Co-author:

White T.R., Silva Aguirre V., Ball W. H., Kepler WG1

Abstract:

Binary stars systems are crucial to better understand the physics of stars, because they might share a common history, enabling us to assume that they have the same age and composition. Furthermore, using the Kepler laws, the orbital parameters could provide tight constraints on their mass ratio. With the recent advent of asteroseismology it is also now possible to look for pulsating multiple stars, providing a new insight on their internal structure and dynamics. Yet, while 60% of stars are thought to be part of multiple system, only a handful were detected with more than one component showing pulsations. I present one of these rare cases, HD 176465. It is composed of two bright stars situated at $49.6 \pm 1.8 pc$, that show pulsations at a similar frequency $\nu_max \approx 3500$ $\mu$Hz. In this poster, I describe our seismic analysis of the system, show the orbits of the stars, discuss their rotations and fundamental physical properties (masses, radii, ages, compositions), derived using various stellar models.

Filipe Pereira

Session: S5a. Poster Session I

1362 views

Date of upload:

16.07.2016

Co-author:

Mário J. P. F. G. Monteiro, João P. S. Faria

Abstract:

A new set of codes, to become publicly available, are presented. These use the frequencies of oscillation of solar-type stars, together with some of the stellar atmospheric parameters, to automatically measure and characterize acoustic glitches in these stars. Both the glitch at the base of the convective zone and at the helium ionization zones are simultaneously measured, using low-degree data.

Orlagh Creevey

Session: S5a. Poster Session I

1350 views

Date of upload:

18.07.2016

Co-author:

Travis Metcalfe, David Salabert, Mathias Schultheis, Rafael Garcia, Savita Mathur, Frederic Thevenin

Abstract:

We present stellar properties of 58 stars from a seismic inference using full-length data sets from Kepler (mass, age, radius, distances). These stars comprise active stars, planet-hosts, solar-analogs, and binary systems. By employing the frequency separation ratios, we test the applicability of the Kjeldsen et al (2008) empirical surface correction. Ensemble analyses exhibit interesting trends, for example, with mixing length parameter or effective temperature. We present ages of binary components and characterize some planetary systems.

Yaqian Wu

Session: S5b. Poster Session II

1785 views

Date of upload:

18.07.2016

Co-author:

M.S.Xiang, X.F.Zhang,T.D.Li,S.L.Bi,X.W.Liu,Y.Huang,J.N.Fu,K.Liu,Z.J.Tian,Z.S.Ge,J.H.Zhang

Abstract:

Main sequence turn-off (MSTO) stars are advantaged indicators of Galactic evo- lution since their ages could be robustly estimated by atmospheric parameters. Hundreds of thousands of MSTO stars have been selected from the LAMOST Galactic survey to study the evolution of the Galaxy, and it will be benefited from accurate estimates of stellar param- eters. In this work, we select 150 MSTO candidates in the LAMOST MSTO stars sample and constrain their stellar parameters with theoretical models. Asteroseismic properties ∆ν, νmaxobtained from Kepler data are considered for accurate estimates. And furthermore, we examine the contamination rate of the LAMOST MSTO stars sample and validate the age estimation by the LAMOST spectra in Xiang et al. (2015). The results show that 79 of the candidates are MSTO stars and others are main-sequence stars or sub giants and a comparison between ages from this work and what have been obtained through interpolation method in Xiang et al. (2015) shows that there is a mean difference of 0.53 Gyr (7%) and a dispersion of 2.71 Gyr (28%). A considerable fraction of oldest stars in the LAMOST MSTO stars sample are likely contamination stars from much younger dwarf/subgiant stars. The main cause for high contamination rates are likely relatively large systematic bias of surface gravity and may not be ignored in the study of Galactic structure.

Jae-Rim Koo

Session: S5b. Poster Session II

1387 views

Date of upload:

20.07.2016

Co-author:

Abstract:

Oscillating Algol-type eclipsing binaries (oEA) are very interesting objects that have three observational features of eclipse, pulsation, and mass transfer. Direct measurement of their masses and radii from the double-lined radial velocity data and photometric light curves would be the most essential for understanding their evolutionary process and for performing the asteroseismological study. We present the physical properties of the oEA star XX Cep from high-resolution time-series spectroscopic data. The effective temperature of the primary star was etermined to be 7,946 +/- 240 K by comparing the observed spectra and the Kurucz models. We detected the absorption lines of the secondary star, which had never been detected in previous studies, and obtained the radial velocities for both components. With the published BVRI light curves, we determined the absolute parameters for the binary via Wilson-Devinney modeling. The masses and radii are M1 = 2.49 +/- 0.06 Msun, M2 = 0.38 +/- 0.01 Msun, R1 = 2.27 +/- 0.02 Rsun, and R2 = 2.43 +/- 0.02 Rsun, respectively. The primary star is about 45 % more massive and 60 % larger than the zero-age main sequence (ZAMS) stars with the same effective temperature. It is probably because XX Cep has experienced a very different evolutionary process due to mass transfer, contrasting with the normal main sequence stars. The primary star is located inside the theoretical instability strip of delta Sct-type stars on HR diagram. We demonstrated that XX Cep is an oEA star, consisting of a delta Sct-type pulsating primary component and an evolved secondary companion.

Jadwiga Daszynska-Daszkiewicz

Session: S5a. Poster Session I

1466 views

Date of upload:

21.07.2016

Co-author:

Przemyslaw Walczak, Alexey Pamyatnykh

Abstract:

The long-time photometric surveys in a few young open clusters allowed to identify the light variability in stars located between the well defined  Scuti variables and Slowly Pulsating B-type stars (Mowlavi et al, 2013, 2015). The period of these changes is in the range of about 0.1 - 0.7 [d] corresponding to the frequencies of about 1.4 - 10 [d-1]. Several objects of this type were suggested also from the analysis of the Kepler data (Balona et al. 2015a). Assuming the pulsational origin of this variability, we test a few hypotheses. Because all these open clusters are very young, we consider only the ZAMS models with the metallicity Z=0.015.

Holger Lehmann

Session: S5b. Poster Session II

1588 views

Date of upload:

25.07.2016

Co-author:

S. Rappaport, B. Kalomeni, and T. Borkovits

Abstract:

There were some 3000 binaries discovered in the Kepler main mission, and there is a growing collection of binaries that have been found to date in the 2-wheel extension of the Kepler mission, called ‘K2’. Among this impressive collection of mostly eclipsing binaries, some 220 triple stars have been detected, mostly through eclipse timing variations, but some via 3rd-body eclipses. In addition to the large sample of triple-star systems, a number of higher-order multiple star systems have also been discovered using Kepler data plus follow-up ground-based observations, like the quadruple systems KIC 4247791 (Lehmann et al. 2012) and KIC 7177553 (Lehmann et al. 2016), or the quintuple system KIC 4150611 (Shibahashi & Kurtz 2012, Prsa et al. 2016). We report on the first quintuple star system found in the K2 fields, and one of the few that contain two eclipsing and spectroscopic binaries.

Magnus Johan Aarslev

Session: S5a. Poster Session I

1393 views

Date of upload:

01.08.2016

Co-author:

Jørgen Christensen-Dalsgaard (SAC), Mikkel N. Lund (a: University of Birmingham, UK. b: SAC), Victor Silva Aguirre (SAC)

Abstract:

The LEGACY sample represents the best solar-like stars observed in the Kepler mission. The 66 stars in the sample are on the main sequence and have more than one year’s data in short cadence, allowing for precise extraction of individual frequencies. We present model fits using the ASTFIT procedure and employing the Ball & Gizon (2014) near-surface effect correction. This correction is based on calculations by Douglas Gough (1990) and includes two terms; one representing a frequency shift corresponding to the increase in pressure scale height that would arise from better modeling of convection and another term correcting for a frequency shift caused by magnetic fields affecting the sound speed without changing the density stratification. Furthermore the correction of each frequency is weighted by the inertia of the corresponding mode. The ASTFIT methods combines the Aarhus stellar evolution code with the Aarhus adiabatic oscillation package to fit individual model frequencies. When combined with the aforementioned correction we produce frequency fits of unprecedented quality – even for stars where the surface term differ significantly from that of the Sun. Our ability to model observations in a precise manner helps constrain the physical parameters of the observed stars as well as pinpoint the aspects of stellar models that still need improvement.

Mag. Erich Hartig

Session: S5a. Poster Session I

1428 views

Date of upload:

10.08.2016

Co-author:

K. Hinkle, National Optical Astronomy Observatories, P.O. Box 26732, Tucson, AZ 85726 USA; T. Lebzelter, University of Vienna, Department of Astrophysics,

Abstract:

The NASA Kepler K2 mission offers new opportunities to search for long period variables (LPVs) along the ecliptic plane. We present first results of our observing proposals for ‘Super-Red-Targets’ in the Kepler K2 Campaigns 0 to 3 (GO0083, GO1003, GO2089, GO3089). The proposal aims at finding and characterizing very red variable objects in the Kepler K2 fields. Selection criteria were 2MASS colours J-Ks greater than 0.8 and Ks less than 8.0 mag plus the availability of some basic information from Simbad, GSC 2.3, 2MASS, and AAVSO data bases to ensure that we select stellar objects only. A main group of stars found with these selection criteria are long period variables (LPV). To focus on these objects we set a lower period limit of 10 days. The usability of K2 for this search is limited since the observation period of an individual target is limited to 80 days. However, this time scale allows detecting LPVs and making an estimate of the period length. Even more than for the Kepler primary mission (see Hartig et al., 2014) the data reduction had to be done with care to extract the true stellar signal. This data reduction is discussed in this poster. For the data preparation we adjusted our pipeline software for TPD, which we used in the Kepler primary mission and modified it to the K2 requirements. While the 6 hours signal caused by the firing of the thrusters for correcting the telescope’s pointing could be easily corrected, a non-linear flux increase over each observation period had to be removed up to campaign C2. This had to be done very carefully since any long time instrumental signal would interfere with a possible long period signal of the star. Furthermore, it turned out that stars with magnitudes < 8.5 Kepmag typically show elongated pixel formats. This has been handled by an appropriate pixel aperture, and so we could improve the light curve’s signal to noise ratio significantly. Some examples are shown. Finally, we compare our results of Campaign 3 with the officially supplied light curves, e.g. Armstrong, et al., 2016, and present our first preliminary results here. Ref.: Armstrong, D. J., Kirk, J., Lam, K. W. F., et al., 2016, MNRAS, 456, 2260 Hartig, E., Cash, J., Hinkle, K. H., et al., 2014, AJ, 148, 123

Pere L. Pallé

Session: S5a. Poster Session I

2804 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.

Ennio Poretti

Session: S5a. Poster Session I

1350 views

Date of upload:

01.09.2016

Co-author:

Monica Rainer, Angelo Mistò, Rosy Panzera

Abstract:

The online archive SISMA (Spectroscopic Indicators in a SeisMic Archive) was created in the framework of the SpaceInn project, with the goal of providing to the scientific community the results of the CoRoT ground-based asteroseismic campaigns. SISMA is an unique blend of high-quality, high-resolution reduced spectra, CoRoT light curves and spectroscopic variability indicators.

Maragrida Cunha

Session: S9. Seismology: Stars Near and in the Main Sequence

1412 views

Date of upload:

05.09.2016

Co-author:

Luis Balona (South African Astronomical Observatory), Daniel Holdsworth (University of Central Lancashire), Guenter Houdek (Stellar Astrophysics Centre, Aarhus University), Karrine Perraut (IPAG, University of Grenoble), Barry Smalley (Keele University, UK)

Abstract:

Chemically peculiar stars are stage to a wide variety of physical phenomena. Progress in the understanding of these objects, through the study of their oscillations, can help us characterize these physical phenomena and better understand the way they are coupled in stars. More than 60 Ap stars are today known to exhibit high frequency oscillations. Despite this, the mechanism responsible for driving these oscillations is still under debate. Currently, the most widely accepted theory states that oscillations in this class of pulsators are excited by the opacity mechanism acting on the hydrogen ionization region, in an envelope where convection has been suppressed by a strong magnetic field. Nevertheless, this theory has been challenged in a number of ways, particularly for its difficulty in reproducing the observed red edge and the very high frequencies observed in some of the well studied pulsators. In this study we revisit the theoretical instability strip proposed by Cunha (2002) and compare the results with the observations for over 60 roAp stars, including 5 stars with exquisite luminosity and effective temperature determinations, derived from a combination of interferometry, parallax, and bolometric flux. The main differences with respect to the previous theoretical work is the exploitation of a larger parameter space and different input physics for the non-adiabatic models. The results show that there is an overall consistency between the position of the known roAp stars in the HR diagram and the predicted Instability strip. However, hints of disagreement are seen when comparing the range of frequencies excited in stellar models and those observed in some stars. This, in turn, points towards the need to re-think the excitation mechanism at work, at least in a sub-group of roAp stars.

Mathieu Vrard

Session: S5b. Poster Session II

1219 views

Date of upload:

06.09.2016

Co-author:

Barban, C & Mosser, B

Abstract:

The Kepler space mission has observed many solar-like pulsators, and helped to decipher their main characteristics (e.g: mass, radius, rotation). Most of the achievements recently obtained in that domain consist of the analysis of the mode frequency positions. However, unique information on non-adiabatic physics derives from the height and width of the modes. In this study, we aim to measure the mode widths in thousands of Kepler red giants and to analyze their behavior in function of stellar parameters as well as seismic parameters. The results unveil a clear dependence on mass and stellar evolution for the star mode width, thus their mode damping.

Ian Roxburgh

Session: S5a. Poster Session I

2206 views

Date of upload:

06.09.2016

Co-author:

Abstract:

The differences between the oscillation frequencies and uncertainty estimates of a star derived by different fitters can be large, sufficiently large so that, were one to find a stellar model that fitted one frequency set ($\chi^2\sim 1$), it does not fit an alternative set. I give 21 examples, comparing frequency sets in common between the Kepler Legacy project and frequency sets from Appourchaux et al (2014) and Davies et al (2015). For 16CygA\&B the differences are large; the $\chi^2$ of the fit of Legacy to Davies's values ranging from 1.64 to 11.47 for 16CygA and 1.62 to 1.79 for 16CygB, depending on which error estimates are used. I analyse both stars in some detail applying my own mode fitting code to both the Legacy and Davies's power spectra and find reasonable agreement with Davies's full frequency sets and very good agreement between values for modes with signal/noise > 1 ($\chi^2 = 0.06, \chi^2_B=0.03$). But the difference with the Legacy values remains large even for modes with S/N>1. I also examine the effects of different power spectra (weighted and unweighted) using the kasoc light curves for Q6-17.2 and Q7-Q16, the effect of different mode height ratios and different rotational splitting and inclination.

Ângela R. G. Santos

Session: S5a. Poster Session I

1320 views

Date of upload:

06.09.2016

Co-author:

Margarida S. Cunha, Pedro P. Avelino, Rafael A. García, Savita Mathur

Abstract:

Starspots are cooler/darker than the stellar surface. Therefore, the total flux of a star changes when spots are visible on its surface. The presence of spots together with the stellar rotation leads to a periodic modulation on the light curve. By studying that modulation one can then learn about the stellar rotation and also magnetic activity. Recently, Reinhold & Arlt (2015) proposed a method based on the analysis of the Lomb Scargle Periodogram (LSP) of the light curve to identify the sign of the differential rotation, i.e. whether the equator rotates faster than the poles or the opposite. In this work, we study in detail the spots’ impact on the light curve and on the resulting LSP. We find that, under some conditions, the LSP can actually provide an estimate of the true spot latitudes and/or the stellar inclination angle. Moreover, we find that the impact of the spot on the ratio between the heights of the second and first harmonics of the main peaks in the LSP can be described by a single parameter, the visibility time of the spot. Finally, we also identify possible sources of false positives/negatives for the sign of the differential rotation.

Ângela R. G. Santos

Session: S5a. Poster Session I

1601 views

Date of upload:

06.09.2016

Co-author:

Margarida S. Cunha, Pedro P. Avelino, William J. Chaplin, Tiago L. Campante

Abstract:

The activity-related variations in the solar acoustic frequencies have been known for 30 years. However, the importance of the different contributions is still not well established. With this in mind, we developed an empirical model to estimate the spot-induced frequency shifts, which takes into account the sunspot properties, such as area and latitude. The comparison between the model frequency shifts obtained from the daily sunspot records and those observed suggests that the contribution from a stochastic component to the total frequency shifts is about 30%. The remaining 70% is related to a global, long-term variation. We also propose a new observable to investigate the short- and mid-term variations of the frequency shifts, which is insensitive to the long-term variations contained in the data. On the shortest time scales the variations in the frequency shifts are strongly correlated with the variations in the total area covered by sunspots. However, a significant loss of correlation is still found, which cannot be fully explained by ignoring the invisible side of the Sun when accounting for the total sunspot area. We also verify that the times when the frequency shifts and the sunspot areas do not vary in a similar way tend to coincide with the times of the maximum amplitude of the quasi-biennial variations found in the seismic data.

Jae Woo Lee

Session: S5b. Poster Session II

1501 views

Date of upload:

14.07.2016

Co-author:

Jae Woo Lee, Kyeongsoo Hong, Seung-Lee Kim, and Jae-Rim Koo

Abstract:

We present both binarity and pulsation of KIC 6220497 from the {\it Kepler} observations. The light curve synthesis shows that the eclipsing system is a semi-detached Algol with parameters of $q$ = 0.243$\pm$0.001, $i$ = 77.3$\pm$0.3 deg, and $\Delta T$ = 3,372$\pm$58 K, in which the detached primary component fills its Roche lobe by $\sim$87\%. A multiple frequency analysis of the eclipse-subtracted light residuals reveals 33 frequencies in the range of 0.75$-$20.22 d$^{-1}$ with amplitudes between 0.27 and 4.56 mmag. Among these, four are pulsation frequencies in fundamental ($f_1$, $f_5$) and $p$ ($f_2$, $f_7$) modes, and six are orbital frequency ($f_8$, $f_{31}$) and its harmonics ($f_6$, $f_{11}$, $f_{20}$, $f_{24}$), which can be attributed to tidally excited modes. For the pulsation frequencies, the pulsation constants of 0.16$-$0.33 d and the period ratios of $P_{\rm pul}/P_{\rm orb}$ = 0.042$-$0.089 indicate that the primary component is a $\delta$ Sct pulsating star and, thus, KIC 6220497 is an oscillating eclipsing Algol (oEA) star. The dominant pulsation period of 0.1174051$\pm$0.0000004 d is significantly longer than that expected from empirical relations that link the pulsation period with the orbital period. The surface gravity of $\log g_1$ = 3.78$\pm$0.03 is clearly smaller than those of the other oEA stars with similar orbital periods. The pulsation period and the surface gravity of the pulsating primary demonstrate that KIC 6220497 would be the more evolved EB, compared with normal oEA stars.

Robert Szabo

Session: S5b. Poster Session II

1427 views

Date of upload:

12.09.2016

Co-author:

K. Kolenberg, L. Molnár, E. Plachy, P. Klagyivik, O. Hanyecz et al.

Abstract:

We have initiated a large survey with K2, to observe thousands of RR Lyrae stars along the ecliptic. The high photometric precision and the 80-90-day continuous coverage will allow us to investigate the light variation of these galactic structure tracer variable stars with an unprecedented detail. The survey will help us to conduct a thorough statistical study of RR Lyrae pulsation dynamics including old and recently discovered dynamical phenomena, like resonances, non-radial modes, period-doubling and the Blazhko-effect. In this talk I describe the survey, present the first results and discuss the prospects in the light of what the combination of the survey and LSST (and also Gaia) will have to offer in the context of galactic structure studies.

Saskia Hekker

Session: S5b. Poster Session II

1463 views

Date of upload:

19.09.2016

Co-author:

Yvonne Elsworth, Sarbani Basu

Abstract:

From its surface proper.es it can be difficult to determine whether a red-giant star is in its Helium-core-burning phase or only burning Hydrogen in a shell around an inert Helium core. Stars in either of these stage can have similar effec.ve temperatures, radii and hence luminosi.es, i.e. they can be located at the same posi.on in the Hertzsprung-Russell diagram. Bedding et al. (2011) showed that with asteroseismic informa.on from the stellar structure it is however possible to iden.fy the evolu.onary state of a red giant. For this technique one relies on the detec.on of the frequencies of mixed pressure-gravity modes. Resolving individual mixed modes is not always feasible in shorter .meseries data such as those of the K2 (Haas et al. 2014) and TESS (Ricker et al. 2015) missions. Here we present two methods that do not rely on the detec.on of the individual mixed modes. These methods have been applied together with the methods by Kallinger et al. (2012) and Mosser et al. (2014) to the APOKASC stars (Pinsonnault et al. in prep; Elsworth et al. in prep) to provide consolidated evolu.onary phases.

Benard Nsamba

Session: S5b. Poster Session II

1519 views

Date of upload:

04.10.2016

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.

Jakob Mosumgaard

Session: S5a. Poster Session I

1485 views

Date of upload:

13.10.2016

Co-author:

Víctor Silva Aguirre, Achim Weiss, Jørgen Christensen-Dalsgaard and Regner Trampedach

Abstract:

How to improve traditional 1D models of stellar structure and evolution using results from sophisticated 3D simulations of stellar atmospheres. More specifically, how T-tau relations from Trampedach et al. (2014, MNRAS, 442, 805) and variable mixing-length parameter from Trampedach et al. (2014, MNRAS, 445, 4366) have been implemented in the Garching Stellar Evolution Code (GARSTEC, see Weiss & Schlattl, 2008, Astrophys. Space Sci., 316, 99).

Lucas Viani

Session: S5b. Poster Session II

1652 views

Date of upload:

19.10.2016

Co-author:

Sarbani Basu

Abstract:

We create isochrones of M67 using the Yale Rotating Stellar Evolution Code. In addition to metallicity, parameters that are traditionally held fixed, such as the mixing length parameter and initial helium abundance, also vary. The amount of convective overshoot is also changed in different sets of isochrones. Models are constructed both with and without diffusion. From the resulting isochrones that fit the cluster, the age range is between 3.6 and 4.8 Gyr and the distance is between 755 and 868 pc. We also confirm Michaud et al. (2004) claim that M67 can be fit without overshoot if diffusion is included.

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