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Towards asteroseismically calibrated age-rotation-activity relations for Kepler solar-like stars

Authors.Garcia, R. A. ; Ceillier, T. ; Salabert, D. ; Mathur, S. ; van Saders, J. L. ; Pinsonneault, M. ; Ballot, J. ; Beck, P. G. ; Bloemen, S. ; Campante, T. L. ; Davies, G. R. ; do Nascimento, J. -D., Jr. ; Mathis, S. ; Metcalfe, T. S. ; Nielsen, M. B. ; Suarez, J. C. ; Chaplin, W. J. ; Jimenez, A. ; Karoff, C.

Journal.Submited to Astronomy & Astrophysics

Abstract.Kepler ultra-high precision photometry of long and continuous observations provide a unique dataset in which surface rotation and variability can be studied for thousands of stars. Because many of these old field stars also have independently measured asteroseismic ages, measurements of rotation and activity are particularly interesting in the context of age-rotation-activity relations. These relations generally lack good calibrators at old ages, a problem that this Kepler sample of stars is uniquely suited to address. We study the surface rotation and the photometric magnetic activity of a subset of 540 solar-like stars on the main-sequence and the subgiant branch for which stellar pulsations have been measured. The rotation period is determined by comparing the results from two different sets of calibrated data and from two complementary analyses. Global photometric levels of magnetic activity in this sample of stars are also extracted by using a photometric activity index, which takes into account the rotation period of the stars. Out of the 540 solar-like pulsating stars in our sample, we successfully measured the rotation period of 310 stars (excluding known binaries and candidate planet host stars). The rotation periods lay between 1 and 100 days. The remaining stars are classified into two categories: those not showing any surface rotation (6 stars), and those in which the four analyses did not converge to a single and robust rotation period (213). The photometric magnetic activity levels were computed and for 61.5% of the dwarfs, its value is comparable to the solar one. We then extract an age-rotation relation only for the dwarfs with very precise asteroseismic age estimations, highlighting the necessity of excluding the hot stars and the subgiants when inferring such relations. We also studied age-activity-rotation relations with a hint of correlation for the subgiants.

Links. NASA ADS,arXiv

Prospects for detecting asteroseismic binaries in Kepler data

Authors. Miglio, A.; Chaplin, W. J.; Farmer, R.; Kolb, U.; Girardi, L.; Elsworth, Y.; Appourchaux, T.; Handberg, R.

Journal. The Astrophysical Journal Letters, Volume 784, Issue 1, article id. L3, 6 pp. (2014)

Abstract. Asteroseismology may in principle be used to detect unresolved stellar binary systems comprised of solar-type stars and/or red giants. This novel method relies on the detection of the presence of two solar-like oscillation spectra in the frequency spectrum of a single lightcurve. Here, we make predictions of the numbers of systems that may be detectable in data already collected by the NASA Kepler Mission. Our predictions, which are based upon TRILEGAL and BiSEPS simulations of the Kepler field of view, indicate that as many as 200 or more “asteroseismic binaries” may be detectable in this manner. Most of these binaries should be comprised of two He-core-burning red giants. Owing largely to the limited numbers of targets with the requisite short-cadence Kepler data, we expect only a small number of detected binaries containing solar-type stars. The predicted yield of detections is sensitive to the assumed initial mass ratio distribution of the binary components and therefore represents a sensitive calibration of the much debated initial mass ratio distribution near mass ratio unity.

Links. NASA ADS, arXiv

Measurement of Acoustic Glitches in Solar-type Stars from Oscillation Frequencies Observed by Kepler

Authors. Mazumdar, A.; Monteiro, M. J. P. F. G.; Ballot, J.; Antia, H. M.; Basu, S.; Houdek, G.; Mathur, S.; Cunha, M. S.; Silva Aguirre, V.; García, R. A.; Salabert, D.; Verner, G. A.; Christensen-Dalsgaard, J.; Metcalfe, T. S.; Sanderfer, D. T.; Seader, S. E.; Smith, J. C.; Chaplin, W. J.

Journal. The Astrophysical Journal, Volume 782, Number 1

Abstract. For the very best and brightest asteroseismic solar-type targets observed by Kepler, the frequency precision is sufficient to determine the acoustic depths of the surface convective layer and the helium ionization zone. Such sharp features inside the acoustic cavity of the star, which we call acoustic glitches, create small oscillatory deviations from the uniform spacing of frequencies in a sequence of oscillation modes with the same spherical harmonic degree. We use these oscillatory signals to determine the acoustic locations of such features in 19 solar-type stars observed by the Kepler mission. Four independent groups of researchers utilized the oscillation frequencies themselves, the second differences of the frequencies and the ratio of the small and large separation to locate the base of the convection zone and the second helium ionization zone. Despite the significantly different methods of analysis, good agreement was found between the results of these four groups, barring a few cases. These results also agree reasonably well with the locations of these layers in representative models of the stars. These results firmly establish the presence of the oscillatory signals in the asteroseismic data and the viability of several techniques to determine the location of acoustic glitches inside stars.

Links. IOP Science, NASA ADS, arXiv

Understanding the dynamical structure of pulsating stars. HARPS spectroscopy of the δ Scuti stars ρ Puppis and DX Ceti

Authors. Nardetto, N.; Poretti, E.; Rainer, M.; Guiglion, G.; Scardia, M.; Schmid, V. S.; Mathias, P.

Journal. A&A Volume 561, January 2014

Abstract. Context. High-resolution spectroscopy is a powerful tool to study the dynamical structure of a pulsating star’s atmosphere.
Aims. We aim at comparing the line asymmetry and velocity of the two δ Sct stars ρ Pup and DX Cet with previous spectroscopic data obtained on classical Cepheids and β Cep stars.
Methods. We obtained, analysed and discuss HARPS high-resolution spectra of ρ Pup and DX Cet. We derived the same physical quantities as used in previous studies, which are the first-moment radial velocities and the bi-Gaussian spectral line asymmetries.
Results. The identification of f = 7.098 d-1 as a fundamental radial mode and the very accurate Hipparcos parallax promote ρ Pup as the best standard candle to test the period–luminosity relations of δ Sct stars. The action of small-amplitude nonradial modes can be seen as well-defined cycle-to-cycle variations in the radial velocity measurements of ρ Pup. Using the spectral-line asymmetry method, we also found the centre-of-mass velocities of ρ Pup and DX Cet, Vγ = 47.49 ± 0.07 km s-1 and Vγ = 25.75 ± 0.06 km s-1, respectively. By comparing our results with previous HARPS observations of classical Cepheids and β Cep stars, we confirm the linear relation between the atmospheric velocity gradient and the amplitude of the radial velocity curve, but only for amplitudes larger than 22.5 km s-1. For lower values of the velocity amplitude (i.e.,

Links. A&A, NASA ADS, arXiv

Limits on surface gravities of Kepler planet-candidate host stars from non-detection of solar-like oscillations

Authors. Campante, T. L.; Chaplin, W. J.; Lund, M. N.; Huber, D.; Hekker, S.; García, R. A.; Corsaro, E.; Handberg, R.; Miglio, A.; Arentoft, T.; Basu, S.; Bedding, T. R.; Christensen-Dalsgaard, J.; Davies, G. R.; Elsworth, Y. P.; Gilliland, R. L.; Karoff, C.; Kawaler, S. D.; Kjeldsen, H.; Lundkvist, M.; Metcalfe, T. S.; Silva Aguirre, V.; Stello, D.

Journal. The Astrophysical Journal, Volume 783, Issue 2, article id. 123, 17 pp.

Abstract. We present a novel method for estimating lower-limit surface gravities log g of Kepler targets whose data do not allow the detection of solar-like oscillations. The method is tested using an ensemble of solar-type stars observed in the context of the Kepler Asteroseismic Science Consortium. We then proceed to estimate lower-limit log g for a cohort of Kepler solar-type planet-candidate host stars with no detected oscillations. Limits on fundamental stellar properties, as provided by this work, are likely to be useful in the characterization of the corresponding candidate planetary systems. Furthermore, an important byproduct of the current work is the confirmation that amplitudes of solar-like oscillations are suppressed in stars with increased levels of surface magnetic activity.

Links. NASA ADS, arXiv

The eccentric massive binary V380 Cyg: revised orbital elements and interpretation of the intrinsic variability of the primary component

Authors. Tkachenko, A.; Degroote, P.; Aerts, C.; Pavlovski, K.; Southworth, J.; Pápics, P. I.; Moravveji, E.; Kolbas, V.; Tsymbal, V.; Debosscher, J.; Clémer, K.

Journal. Monthly Notices of the Royal Astronomical Society

Abstract. We present a detailed analysis and interpretation of the high-mass binary V380 Cyg, based on high-precision space photometry gathered with the Kepler space mission as well as high-resolution ground-based spectroscopy obtained with the HERMES spectrograph attached to the 1.2 m Mercator telescope. We derive a precise orbital solution and the full physical properties of the system, including dynamical component mass estimates of 11.43 ± 0.19 and 7.00 ± 0.14 M⊙ for the primary and secondary, respectively. Our frequency analysis reveals the rotation frequency of the primary in both the photometric and spectroscopic data and additional low-amplitude stochastic variability at low frequency in the space photometry with characteristics that are compatible with recent theoretical predictions for gravity-mode oscillations excited either by the convective core or by sub-surface convective layers. Doppler imaging analysis of the silicon lines of the primary suggests the presence of two high-contrast stellar surface abundance spots which are located either at the same latitude or longitude. Comparison of the observed properties of the binary with present-day single-star evolutionary models shows that the latter are inadequate and lack a serious amount of near-core mixing.

Links. MNRAS, NASA ADS, arXiv

Pulsating red giant stars in eccentric binary systems discovered from Kepler space-based photometry

Authors. Beck, P. G.; Hambleton, K.; Vos, J.; Kallinger, T.; Bloemen, S.; Tkachenko, A.; García, R. A.; Østensen, R. H.; Aerts, C.; Kurtz, D. W.; De Ridder, J.; Hekker, S.; Pavlovski, K.; Mathur, S.; De Smedt, K.; Derekas, A.; Corsaro, E.; Mosser, B.; Van Winckel, H.; Huber, D.; Degroote, P.; Davies, G. R.; Prša, A.; Debosscher, J.; Elsworth, Y.; Nemeth, P.; Siess, L.; Schmid, V. S.; Pápics, P. I.; de Vries, B. L.; van Marle, A. J.; Marcos-Arenal, P.; Lobel, A.

Journal. Accepted for publication in Astronomy & Astrophysics

Abstract. The unparalleled photometric data obtained by NASA’s Kepler space telescope led to an improved understanding of red giant stars and binary stars. Seismology allows us to constrain the properties of red giants. In addition to eclipsing binaries, eccentric non-eclipsing binaries, exhibiting ellipsoidal modulations, have been detected with Kepler. We aim to study the properties of eccentric binary systems containing a red giant star and derive the parameters of the primary giant component. We apply asteroseismic techniques to determine masses and radii of the primary component of each system. For a selected target, light and radial velocity curve modelling techniques are applied to extract the parameters of the system. The effects of stellar on the binary system are studied. The paper presents the asteroseismic analysis of 18 pulsating red giants in eccentric binary systems, for which masses and radii were constrained. The orbital periods of these systems range from 20 to 440days. From radial velocity measurements we find eccentricities between e=0.2 to 0.76. As a case study we present a detailed analysis of KIC5006817. From seismology we constrain the rotational period of the envelope to be at least 165 d, roughly twice the orbital period. The stellar core rotates 13 times faster than the surface. From the spectrum and radial velocities we expect that the Doppler beaming signal should have a maximum amplitude of 300ppm in the light curve. Through binary modelling, we determine the mass of the secondary component to be 0.29$pm$0.03,$M_odot$. For KIC5006817 we exclude pseudo-synchronous rotation of the red giant with the orbit. The comparison of the results from seismology and modelling of the light curve shows a possible alignment of the rotational and orbital axis at the 2$sigma$ level. Red giant eccentric systems could be progenitors of cataclysmic variables and hot subdwarf B stars.

Links. NASA ADS, arXiv

Peak-bagging in Helio- and Asteroseismology

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

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

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

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

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

Important dates:

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

Propagating Linear Waves in Convectively Unstable Stellar Models: A Perturbative Approach

Authors. Papini, E.; Gizon, L.; Birch, A. C.

Journal. Solar Physics, Volume 289, Issue 6, pp.1919-1929

Abstract. Linear time-domain simulations of acoustic oscillations are unstable in the stellar convection zone. To overcome this problem it is customary to compute the oscillations of a stabilized background stellar model. The stabilization affects the result, however. Here we propose to use a perturbative approach (running the simulation twice) to approximately recover the acoustic wave field while preserving seismic reciprocity. To test the method we considered a 1D standard solar model. We found that the mode frequencies of the (unstable) standard solar model are well approximated by the perturbative approach within 1 μHz for low-degree modes with frequencies near 3 mHz. We also show that the perturbative approach is appropriate for correcting rotational-frequency kernels. Finally, we comment that the method can be generalized to wave propagation in 3D magnetized stellar interiors because the magnetic fields have stabilizing effects on convection.

Links. Solar Physics, NASA ADS, arXiv

A search for pulsations in the HgMn star HD 45975 with CoRoT photometry and ground-based spectroscopy

Authors. Morel, T.; Briquet, M.; Auvergne, M.; Alecian, G.; Ghazaryan, S.; Niemczura, E.; Fossati, L.; Lehmann, H.; Hubrig, S.; Ulusoy, C.; Damerdji, Y.; Rainer, M.; Poretti, E.; Borsa, F.; Scardia, M.; Schmid, V. S.; Van Winckel, H.; De Smedt, K.; Papics, P. I.; Gameiro, J. F.; Waelkens, C.; Fagas, M.; Kaminski, K.; Dimitrov, W.; Baglin, A.; Michel, E.; Dumortier, L.; Fremat, Y.; Hensberge, H.; Jorissen, A.; Van Eck, S.

Journal. Astronomy & Astrophysics, Volume 561, id.A35, 14 pp.

Abstract. The existence of pulsations in HgMn stars is still being debated. To provide the first unambiguous observational detection of pulsations in this class of chemically peculiar objects, the bright star HD 45975 was monitored for nearly two months by the CoRoT satellite. Independent analyses of the light curve provides evidence of monoperiodic variations with a frequency of 0.7572 c/d and a peak-to-peak amplitude of ~2800 ppm. Multisite, ground-based spectroscopic observations overlapping the CoRoT observations show the star to be a long-period, single-lined binary. Furthermore, with the notable exception of mercury, they reveal the same periodicity as in photometry in the line moments of chemical species exhibiting strong overabundances (e.g., Mn and Y). In contrast, lines of other elements do not show significant variations. As found in other HgMn stars, the pattern of variability consists in an absorption bump moving redwards across the line profiles. We argue that the photometric and spectroscopic changes are more consistent with an interpretation in terms of rotational modulation of spots at the stellar surface. In this framework, the existence of pulsations producing photometric variations above the ~50 ppm level is unlikely in HD 45975. This provides strong constraints on the excitation/damping of pulsation modes in this HgMn star.

Links. A&A , NASA ADS, arXiv